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The 7 most important cannabis research studies of 2023

2023 saw tons of new research come out related to cannabis. Below is a selection of some of the studies that caught my attention, with brief summaries of each. The first two studies are in the realm of public health. After that, three studies on commercial cannabis followed by two basic research studies on the endocannabinoid system.

This year, we saw a nice review of the public health research done over the past few years, finding little evidence that legalization promotes marijuana consumption among teens, together with evidence that does promote lower teen alcohol consumption. There was also interesting research done on the Cannabis plant itself, including non-terpene volatiles that drive its aroma and its susceptibility to Hop Latent Viroid , a devastating infection that’s spreading across North America. There was also interesting basic research, shedding new light on how the endocannabinoid system works.

Here’s a brief summary of a selection of studies from 2023.

The Public Health Effects of Legalizing Marijuana

As of the publication of this paper, 36 states had legalized medical marijuana and 18 had legalized recreational adult-use cannabis. This review paper summarizes studies that have come out to do with public health consequences of legalization. The major outcomes they reviewed the literature on included: youth marijuana use, alcohol consumption, the abuse of prescription opioids, traffic fatalities, and crime.

• “Little credible evidence to suggest that legalization promotes marijuana use among teenagers.”

Topics with a strong level of agreement across studies included:

• “Convincing evidence that young adults consume less alcohol when medical marijuana is legalized.”

For other topics, the authors found a lower level of agreement across studies preventing firm conclusions from being drawn. Those included:

• “For other public health outcomes such as mortality involving prescription opioids, the effect of legalizing medical marijuana has proven more difficult to gauge and, as a consequence, we are less comfortable drawing firm conclusions.”

For more detail on the literature they reviewed, check out the paper itself .

State Cannabis Legalization and Psychosis-Related Health Care Utilization

The question this study sought to address was whether state cannabis legalization was associated with increased rates of psychosis-related health care claims. This cohort study looked at claims data from over 63 million beneficiaries between 2003-2017. They found no statistically significant differences in the rates of psychosis-related diagnoses or prescribed antipsychotics in states with legal medical or adult-use cannabis compared to those without legal cannabis.

Minor, Nonterpenoid Volatile Compounds Drive the Aroma Differences of Exotic Cannabis

Following up on previous work showing that the “skunky” aroma of some strains comes not from terpenes, but from a class of compounds called, “volatile sulfur compounds,” a team from Abstrax dug deeper into the chemistry of cannabis aroma. They found that a variety of nonterpene volatile compounds are the main drivers of many of the “exotic” aromas that give strains various sweet or savory scents. 

To learn more about this particular study, check out this Leafly article and listen to the video lecture by Abstrax chemist Dr. Iain Oswald.

Symptomology, prevalence, and impact of Hop latent viroid on greenhouse-grown cannabis (Cannabis sativa L.) plants in Canada

Hop latent viroid is a virus-like infection that’s been devastating cannabis crops throughout North America. We have previously written about what HLV is and how it affects marijuana growers. This was a key study from 2023 showing what HLV does to Cannabis plants and how prevalent it already is in some locations. Given the enormous impact HLV is already having, expect to hear more about this bug in 2024.

Comparison of the Cannabinoid and Terpene Profiles in Commercial Cannabis from Natural and Artificial Cultivation

Some cannabis is grown indoors, some outdoors. Many consumers have strong opinions on which is better. In this 2023 study , researchers did a head-to-head comparison of two genetically identical cultivars grown indoors vs. outdoors, looking at their cannabinoid and terpene content. Main findings included:

• Significantly higher levels of oxidized and degraded cannabinoids in indoor-grown samples.
• Significantly more “unusual cannabinoids” such as C4- and C6-THCA in outdoor-grown samples.
• Significant differences in terpene profiles for outdoor- vs. indoor-grown samples, with outdoor-grown samples generally showing higher levels of sesquiterpenes like caryophyllene, humulene, etc.

Disruption of tonic endocannabinoid signaling triggers cellular, behavioral and neuroendocrine responses consistent with a stress response

The endocannabinoid system regulates many different systems in the brain and body. As we covered in this article , endocannabinoids play an important role in regulating pain perception, fear, and anxiety. At any given moment, there is a certain level of “endocannabinoid tone” in your brain. As this rodent study showed, endocannabinoid tone “gates” the stress response generated in the hypothalamus of the brain. In general, endocannabinoids restrict activation of the hypothalamic-pituitary-adrenal (HPA) axis, which is the key brain system regulating stress levels. Higher endocannabinoid tone had the effect of lessening stress levels in rodents. 

Cannabinoid CB1 Receptors Are Expressed in a Subset of Dopamine Neurons and Underlie Cannabinoid-Induced Aversion, Hypoactivity, and Anxiolytic Effects in Mice

Endocannabinoid receptors are one of the most abundant proteins in the brain, found in many different brain regions and types of neurons. This is one reason why the effects of THC can be so diverse. Depending on the dose of THC consumed, different neurons and brain regions can be affected to different degrees, generating different effects. In this rodent study , neuroscientists studied the effects of a specific subset of dopamine neurons in the brain which express CB1 receptors. They found that this particular subset of neurons has some of the negative side effects that cannabinoids like THC can induce (especially at high doses), including anxiety. This highlights how specific subsets of neurons in the brain can control specific effects that cannabinoids generate.

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After 50 Years, U.S. Opens The Door To More Cannabis Crops For Scientists

More than 30 states have medical marijuana programs — yet scientists are only allowed to use cannabis plants from one U.S. source for their research. That's set to change, as the federal government begins to add more growers to the mix. Drew Angerer/Getty Images hide caption

More than 30 states have medical marijuana programs — yet scientists are only allowed to use cannabis plants from one U.S. source for their research. That's set to change, as the federal government begins to add more growers to the mix.

After more than 50 years, the federal government is lifting a roadblock to cannabis research that scientists and advocates say has hindered rigorous studies of the plant and possible drug development.

Since 1968, U.S. researchers have been allowed to use cannabis from only one domestic source : a facility based at the University of Mississippi, through a contract with the National Institute on Drug Abuse (NIDA).

That changed earlier this month, when the Drug Enforcement Administration announced it's in the process of registering several additional American companies to produce cannabis for medical and scientific purposes.

It's a move that promises to accelerate understanding of the plant's health effects and possible therapies for treating conditions — chronic pain, the side effects of chemotherapy, multiple sclerosis and mental illness, among many others — that are yet to be well studied .

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"This is a momentous decision," says Rick Doblin, executive director of the Multidisciplinary Association for Psychedelic Studies (MAPS), which has spearheaded research into other Schedule 1 drugs — the most restrictive class of controlled substance, which the federal government defines as "drugs with no currently accepted medical use."

"This is the last political obstruction of research with Schedule 1 drugs," he says.

About one-third of Americans currently live in a state where recreational marijuana is legal — and more than 30 states have medical marijuana programs . Yet scientists still aren't allowed to simply use the cannabis sold at state-licensed dispensaries for their clinical research because cannabis remains illegal under federal law.

Medical Marijuana's 'Catch-22': Limits On Research Hinder Patient Relief

"It is a big disconnect," says Dr. Igor Grant , a psychiatry professor and director of the Center for Medicinal Cannabis Research at University of California, San Diego.

The new DEA decision doesn't resolve the conflict between federal and state laws, but it does offer researchers a new, federally sanctioned pipeline for more products and strains of cannabis.

"We'll see a decade or more of explosive cannabis research and potential new therapies," says Dr. Steve Groff, founder and chairman of Groff North America , one of three companies that has publicly announced it has preliminary approval from the federal government to cultivate cannabis for research.

A long-running fight to overturn federal "monopoly"

Despite their efforts, scientists have encountered administrative and legal hurdles to growing pharmaceutical-grade cannabis for decades.

In 2001, Dr. Lyle Craker, a prominent plant biologist, first applied for a license to cultivate marijuana for research — only to encounter years of delay that kicked off a prolonged court battle with the DEA, which has to greenlight research into Schedule 1 drugs like cannabis.

"There's thousands of different cannabis varieties that all have unique chemical profiles and produce unique clinical effects, but we didn't have access to that normal diversity," says Dr. Sue Sisley , a cannabis researcher and president of the Scottsdale Research Institute, which also received preliminary DEA approval to produce cannabis for research.

Only in 2016 did the federal government signal a change in policy that would open the door for new growers, but applications to do so languished for years. Craker and others ended up suing the federal government over the delay.

Psychiatrist Explores Possible Benefits Of Treating PTSD With Ecstasy Or Cannabis

Sisley has long taken issue with the supply of cannabis coming from the NIDA facility in Mississippi — in particular, how it's processed. She used cannabis produced there in her recently published clinical trial on treating PTSD in military veterans.

She describes the product as an "anemic" greenish powder.

"It's very difficult to overcome the placebo effect when you have something that diluted," she says.

The 76-person study, which took 10 years to complete, concluded that smoked cannabis was generally well tolerated and did not lead to deleterious effects in this group. But it also did not find any statistically significant difference in abating the symptoms of PTSD when compared to a placebo.

For Grant of UCSD, the problem with the long-standing supply of cannabis isn't so much the quality, but the lack of different products like edibles and oils and of cannabis strains with varying concentrations of CBD and THC, the plant's main psychoactive ingredient.

"We don't have enough research on the kind of marijuana products that people in the real world are using," he says.

As CBD Oils Become More Popular, The FDA Considers Whether To Set New Rules

Because of the limited domestic supply, some researchers have resorted to importing cannabis from outside the U.S. — a legal but wildly counterintuitive arrangement that is "arduous" and prone to hiccups, says Sisley.

The constraints on research cannabis also has impeded the pathway to drug development because the NIDA facility's cannabis could only be used for academic research, not for prescription drug development . A drug studied in phase 3 clinical trials — what's required before submitting for approval from the Food and Drug Administration — must be the same as what's later marketed.

"The NIDA monopoly has primarily been why we have medical marijuana in the states, but we don't have medical marijuana through the FDA," says Doblin of MAPS. "It's a fundamental change that we can now have drug development with domestic supplies."

A few barriers still remain

The few companies that will soon land DEA spots to cultivate cannabis have an eager marketplace of researchers who are "clamoring" for the chance to study the scientific properties and medical potential of the plant, says Groff, whose company is up for DEA approval and who also has an FDA project to study the antimicrobial properties of cannabis for killing dangerous bacteria like MRSA .

By the end of next year, Groff anticipates his company will be producing up to 5,000 pounds of marijuana per year, offering researchers a "full menu of customizable options."

Biopharmaceutical Research Company — a third company that will soon cultivate cannabis with a DEA license — already has dozens of agreements in place with U.S. researchers and is hearing from more academic institutions, drugmakers and biotech companies in the wake of the change in policy, says CEO George Hodgin.

"Now there's a very clear, approved and legal path for them to legally enter the cannabis space in the United States," says Hodgin.

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Washington State University's Center for Cannabis Policy, Research and Outreach is one of the places that expects to eventually procure cannabis from Hodgin's business.

"It's definitely a big step in the right direction because the industry is moving much faster than we are in research," says Michael McDonell , an associate professor of medicine and director of the university's cannabis center.

But he also points out that even with more growers coming online, it's still by no means easy to study cannabis, because researchers need a special license when working with a Schedule 1 drug and grants to conduct these studies are hard to come by.

Despite the widespread use of marijuana in the U.S., research into the medical potential of other Schedule 1 drugs like MDMA (ecstasy) is much further along than cannabis .

UCSD's Grant says the biggest leap forward for research would come from moving cannabis out of the Schedule 1 drug classification. "If that were to happen," he says, "that would solve a lot of these problems that we've been talking about."

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Breaking new ground in cannabis research

Alexandra Kritikos, PhD’21, is pioneering new methods and data sets to uncover real-world trends among medical marijuana patients

February 15, 2022

While some industries faltered during the COVID-19 pandemic, cannabis was not one of them. U.S. sales of legal marijuana—both medical and recreational—reached $17.5 billion in 2020, an increase of 46 percent from the previous year. In Massachusetts, a surge of applicants received medical marijuana cards through telehealth appointments with state-certified physicians, granting them access to an array of cannabis-derived products—from tinctures to vape cartridges to infused lotions.   

Yet even as cannabis is prescribed to treat everything from sore muscles to cancer, there is much that policymakers and physicians don’t know about the drug and its users. For health economist Alexandra Kritikos, PhD’21, who got her start researching tobacco use among youth in Greece, the gray area surrounding cannabis—which has been legalized for medical use in 39 states, but remains illegal at the federal level—presented a fascinating challenge. 

“The more I read, the more gaps I found in the literature,” says Kritikos, who studied health and behavioral health policy at Heller. “Prescribers are telling their patients, ‘Yes, you might be able to try cannabis for this reason,’ but do we actually know anything about dosing? About how much to take and what type? We don’t.”

An ambitious agenda

In 2016, Kritikos began a four-and-a-half year dissertation journey focused on medical marijuana patients in New York State, hoping to uncover usage patterns and demographic trends that could help legislators and healthcare workers better understand the medical cannabis landscape. 

Her approach was nontraditional by necessity: Since clinical trials of cannabis are curtailed by federal regulations, Kritikos utilized sales data collected by local dispensaries as part of the state’s mandatory cannabis seed-to-sale tracking platform, in which every every plant’s growth, cultivation, and selling process is recorded. The data gave Kritikos a crucial window into the purchasing history of patients over a three-year period, including what form of cannabis they purchased, how often they purchased it, and its potency (products can contain high or low levels of either THC or CBD, both chemical compounds which are derived from cannabis but affect the body differently). The data also included demographic information for each patient, such as age and gender, and their approved medical condition.

While previous studies have analyzed aspects of seed-to-sale data, Kritikos’ was the first to link patient demographics with purchasing behavior. In her three-part dissertation, which she defended in May, Kritikos reported groundbreaking findings on the buying patterns of various categories of patients, describing quantifiable differences between customers of different ages, genders, and those who use cannabis to treat physical pain versus other conditions, including mental disorders.

Using a methodology borrowed from opioid studies, Kritikos’ dissertation also examined how patients’ behavior changed over time, both in the amount of product used and its strength. From there, she was able to quantify an average dose of THC, something the National Institute on Drug Abuse (NIDA) had identified as a top research priority.

Being able to identify a “standard dose” of cannabis, as one does with Tylenol or any prescription drug, is a crucial step forward for policymakers looking to prevent misuse of the drug, and for doctors who prescribe cannabis to their patients, said Rosalie Pacula, a drug policy economist and professor of health policy and management at the University of Southern California who was on Kritikos’ dissertation committee. 

“The bench science has lagged far behind the public policy here, so we know very little about the motivations of patients who use medical cannabis as well as the trajectories of their medical use,” she says. “Alexandra’s dissertation provides very useful information on practical use patterns being observed in the real world.”

Kritikos’ dissertation findings are already being used to inform policy recommendations in Massachusetts. In October, her research was cited multiple times in a report issued by the Massachusetts Cannabis Control Commission. The Commission’s director of research Julie Johnson, PhD’15, who served on Kritikos’ dissertation committee, lauded Kritikos’ novel use of seed-to-sale data to assess patient behaviors, including whether they regularly consume alcohol and cannabis simultaneously.  

“As science comes to better understand the myriad societal effects—including public health, public safety, clinical and economical effects—policymakers can more effectively regulate the legal industry in a way that protects the public’s interests while allowing safe access to cannabis for adults and patients,” she says. 

Entering the policy world

Kritikos arrived at Heller after earning a master’s degree in applied economics from Northeastern University and quickly became enamored with the school’s multidisciplinary approach to public policy. 

“People were coming together and thinking about research questions from so many different lenses,” she recalls. “I loved it.” 

While working on her dissertation, Kritikos was supported by mentors from across Heller, including Johnson and Professor Dominic Hodgkin, who served as her advisor and chaired her dissertation committee. Hodgkin, also an economist, praised Kritikos for her creativity and resourcefulness as a researcher in an emerging field: “Alexandra's study helps to fill the knowledge gap about this emerging delivery model for medical cannabis,” he says.

Ultimately, her Heller experience solidified Kritikos’ passion for health economics. In August, she began a new position as a postdoctoral researcher at University of Southern California, working under Pacula at the Schaeffer Center for Health Policy & Economics. The research questions she’ll be exploring are uncharted, such as whether medical dispensaries are influenced by recreational shops or how innovations like THC-infused beverages and vaping devices are impacting patient behavior, but Kritikos is comfortable operating without a roadmap. 

“My dissertation was very difficult because there were no guidelines and no code books for me to use,” she says. “I’m happy I could shed some light on this topic and help future policymakers evaluate cannabis with the same guidelines as any other medication.”

Harvard researcher breaks down the health benefits and risks of cannabis

In 2018, Massachusetts legalized the recreational sale and consumption of cannabis for adults. Since then, the cannabis has steadily grown statewide, with more than 250 dispensaries opening up and sales totaling more than $1.5 billion last year alone. Since 2012, 23 states and the District of Columbia have legalized recreational cannabis for adult use and recent studies show that nearly 18% of Americans have used it in the last four years. Despite this recent embrace of cannabis, lingering questions still remain about the health risks and benefits associated with using it. To help us get a better understanding of what the latest research tells us, GBH's All Things Considered host Arun Rath spoke to Dr. Peter Grinspoon, a cannabis specialist and instructor in medicine at Harvard Medical School. He's also the author of "Seeing Through the Smoke: A Cannabis Specialist Untangles The Truth About Marijuana".

Rath: To start off, I'm curious about the current state of cannabis research. I know that for quite a long time it was difficult to actually do the research and I get the impression that in the last few years we've seen some worthwhile studies. Is that the case and what have we learned?

Grinspoon: Well, absolutely. First of all, there's been cannabis research all along, but because of the war on drugs and the U.S. government's policy, virtually all of the research was oriented towards finding harms, not into finding benefits. To be funded over the last 50 years in cannabis research, you had to find a drop in IQ or drop in sperm count, a drop in motivation, or something harmful about cannabis. Finally, that's starting to lighten up a little bit, and we're able to research both the benefits as well as harms. However, I do want to mention that cannabis is still scheduled as Schedule One in the Controlled Substance Act, which by definition says no medical utility and high abuse liability, neither of which is true. Obviously, it has lots of medical utility and there are several cannabis derived FDA-approved drugs on the market. So, it has medical utility and it has low to moderate abuse liability, not high abuse liability. The fact that it's still a Schedule One, where we lock up the most onerous and dangerous drugs, it makes it very difficult to do research. We are doing better and more balanced research now, but a lot of the research is happening, for better or worse, in other countries, such as in Europe and in Israel, where they don't have such strict and onerous restrictions on cannabis research.

Rath: What are some of the big discoveries that have been made recently?

Grinspoon: Well, it's a little hard to generalize. There were 1400 studies that came out in the year 2022. People have a lot of confirmation bias with cannabis, but what I think is coming out, the things that I find really interesting, are that with legalization, teen use has not been rising, which is really good. I think we're finding increasingly that cannabis is helpful in older Americans, particularly to help them get off many of the other drugs, the polypharmacy, that they're afflicted with. We're continuing to learn that cannabis can be a helpful way to treat both insomnia, chronic pain, and because it could treat chronic pain, it could help mitigate many of the harms that we find with other pain medications such as opiates or non-steroidals, which cause a lot of heart attacks, a lot of ulcers, and a lot of kidney disease. So, I think we're confirming a lot of what people have been saying anecdotally in terms of the benefits now that we're more able to study the benefits of cannabis.

Rath: I also know from our reporting about some experimental uses showing promise for relief for patients with dementia and other neurological problems.

Grinspoon: When I look at medical cannabis as a clinician, I don't say, "Is cannabis safe?" I say, "Is cannabis safer than whatever else I'd be using?" And the medications we use for older Americans, in general, tend to be more dangerous. That's why cannabis for many of them is a palatable alternative. For dementia, there's no great treatment yet. But for many of the behavioral disturbances and problems – the aggression, the confusion, and the anxiety – we tend to load these patients up on heavy-duty neuroleptics such as Haldol and Thorazin, and people are finding cannabis to be a much more palatable option. It results almost universally, if you look at the studies, in an improved quality of life.

Rath: Getting to the point that you were just making about safe versus safer, we've also seen some recent studies that seem to correlate the availability of cannabis with lower rates of opioid overdoses.

Grinspoon: Absolutely. I've been treating people with opiate addiction for at least the last decade, and I find cannabis to be very helpful in a number of ways in terms of helping people who are addicted to opiates. It helps with the pain, the anxiety, the insomnia and when they're withdrawing from opiates. Unfortunately, I can say I have personal experience. Fifteen years ago, when I was addicted to opiates, cannabis was much more effective than any of the other medications for opiate withdrawal symptoms, which are just miserable. You don't die from them, but they're utterly miserable. Now, the one area that I don't think we've arrived at yet is with methadone and buprenorphine, also known as Suboxone. We have very good data that there's a 50% to 80% reduction in overdose deaths, and we don't have that evidence yet for cannabis. So, I certainly use it to get people off opiates and for chronic pain, but when it comes to opiate addiction, I usually prescribe Suboxone and use cannabis as an adjunct just because there isn't the same level of data, and all other things being equal, you have to go with the data.

Rath: Back to the risk, you mentioned how earlier studies had a certain confirmation bias looking for bad things with cannabis. With recent research, do we have a better understanding of what risks there may be?

Grinspoon: My dad was a legendary cannabis specialist at Harvard Medical School for a half century at least, Dr. Lester Grinspoon. Something very clever he used to say, was that we spent so much money trying to vilify and prove harm with cannabis, that we actually have proven that, relatively speaking, it's fairly safe. A lot of harms just haven't panned out. For example, they tried so hard to show that cannabis causes lung cancer. While doctors don't recommend that you smoke anything, cannabis just hasn't been associated with lung cancer. That said, there are certain populations that we don't recommend cannabis for because it's much more dangerous. We don't recommend that teenagers use it because it can harm their developing brains. We say to teenagers, "just say wait." We don't say, "just say no." For pregnant women or breastfeeding women, there's no evidence that it's safe in these conditions. Again, this can come back to what is safer because if someone has severe chronic pain, for example, when they're pregnant, none of the other medications are particularly safe either. So, you try to figure out which is the least toxic alternative, which is part of what's so stressful about being a doctor in general. Lastly, people with a history or family history of psychosis should certainly avoid cannabis because it can exacerbate or worsen the psychosis. So, there are people that shouldn't use cannabis or use it with extreme caution. Generally, if you're not in any of those categories and you use it modestly and responsibly, it's a fairly safe medication.

Rath: Dr. Grinspoon, always fascinating talking with you. Thank you so much.

Grinspoon: My pleasure. Thank you so much for these great questions.

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• What’s New in Cannabis Research

Monthly updates on cannabis and cannabinoid research, by…

June 4, 2021

An original investigation conducted by Arkell et al. assayed the effects of cannabidiol (CBD) compared to ∆9-Tetrahydrocannabidiol (THC) on driving performance. The study investigated the effects of vaporized THC-dominant versus CBD-dominant cannabis o …

March 1, 2021

Regular use of cannabis high in delta-9-tetrahydrocannabinol (THC) is associated with increased risk of psychotic symptoms among young people. This finding has not been explored as deeply in adults who use cannabis-based medications. Velayudhan et al. …

February 12, 2021

Post-Traumatic Stress Disorder (PTSD) is characterized by intrusive memories of life-threatening events accompanied by severe anxiety and sleeplessness that often adversely affect quality of life. PTSD has been reported to have a life-time prevalence o …

January 25, 2021

Cannabinoid receptor activation is known to ameliorate inflammatory bowel disease (IBD) in animal models, but the contributions of other factors in combination with receptor activation remain unstudied. Cannabinoids bind to G protein coupled receptors …

December 10, 2020

This study assesses cannabidiol, which inhibits the reuptake of endocannabinoids, as a treatment for cannabis use disorder. Freeman et al. (2020) conducted a phase 2a, randomized, double-blind, placebo, controlled, clinical trial investigating the heal …

July 20, 2020

Sickle cell disease affects approximately 100,000 Americans. It is a genetic disease characterized by chronic pain and extremely painful episodes, which usually require treatment with large doses of opioids for extended periods of time. Opioids have a …

March 2, 2020

With increasing availability of cannabis products and its decriminalized status in many states, understanding its acute and residual effects on driving is important in promoting public health and in guiding law enforcement with implementations of legal …

January 31, 2020

Cannabis has shown promise in treating several medical conditions but its effects on pregnant women and developing fetuses is unknown. This study aimed to investigate the association of self-reported cannabis use by pregnant women and unfavorable mater …

This review article analyzed nine peer-reviewed studies focused on the effects of cannabinoids on Alzheimer’s disease and dementia. Due to the increasing life expectancy in society aging related Alzheimer’s disease onset has continued to increase since …

December 4, 2019

Cannabidiol’s anxiolytic effects have been demonstrated in several studies. However, the mechanism for this effect remains to be elucidated. The present paper offers additional data that may aid in future research in understanding endocannabinoids’ rol …

October 15, 2019

Benzodiazepines (BDs) like Xanax, are a class of medications used for anxiety, seizures, insomnia, and a variety of other neurological/psychiatric conditions. The adverse side effects of BDs are well documented and include dependence, addiction, withdr …

September 11, 2019

This paper reports that incidences of pediatric cannabis exposure in Massachusetts increased following medical marijuana legalization. The study analyzed cannabis exposure cases amongst individuals aged 0-19 reported to the Regional Center for Poison C …

August 27, 2019

The issue of JAMA published on August 09, 2019 includes an entire section on cannabis curated by Kevin Hill. Topics include cannabis use for medical purposes such as chronic pain and cancer treatment.

August 10, 2019

Currently, there is not enough significant data to conclude that THC or any other cannabinoid is harmful to a developing fetus. This study of 367,403 pregnancies among women in Northern California, reports that the relative rates of daily, weekly, and …

Up to 7.5% of pregnant women in the United States use cannabis during their pregnancy. The concentration of THC in cannabis is increasing as is the number of pregnant women who use cannabis. It is critical that the developmental risk of THC and its mai …

Approximately 35% of Americans suffer from obesity and its related health effects. The activation of cannabinoid 1 receptor [CB1R] has been shown to increase body weight, appetite, insulin resistance, and fat cell production. Thus, overactivity of CB1R …

June 21, 2019

Adolescence is a critical period marked by complex neurological processes and is frequently associated with mood fluctuations and impulsivity. Consequently, understanding the effects of cannabis use during this developmental stage is essential in order …

May 28, 2019

Due to the increasing rates of tobacco and cannabis use co-occurrence among individuals seeking treatment for cannabis use disorder (CUD), appropriate timing of tobacco intervention (TI) initiation is important in maximizing the effects of both the CUD …

February 6, 2019

Cannabis’ increasing popularity is paralleled by growing concerns about its habit-forming propensity along with other important public health concerns including but not limited to driving under the influence and availability to adolescents. This double …

As the cannabis market expands, consumers face a wide variety of products with different methods of consumption such as vaporizing, smoking, edible formulations, etc., Thus, rigorous analyses of pharmacokinetics and pharmacodynamics for each route of c …

Cannabidiol, a non-intoxicating constituent of cannabis, has been implicated as a possible anxiolytic and anti-epileptic with the FDA recently approving a drug to treat epilepsy with cannabidiol as its primary ingredient. The present study aims to exam …

December 16, 2018

Over 12 million births in the US were analyzed to identify pregnant women who use cannabis and to assess obstetric and neonatal outcomes. The results showed that the incidence of cannabis dependence in 2013 is two-times more than in 1999 and that canna …

This review provides insights on three clinical trials that showed cannabidiol’s efficacy in reducing seizure episodes by at least 38%. More importantly, this review highlights the need for further research to fully elucidate CBD’s mechanism of action …

Despite increasing evidence of cannabinoids’ analgesic properties, concerns regarding its potential for abuse limit its utility in pain management. The present study posits a solution to such valid and thoughtful concern. GAT211 is a novel compound tha …

December 14, 2018

With the legalization of cannabis in many states, it is imperative that policies are adopted based on scientific findings. This study, conducted in Canada, where recreational use of cannabis recently became legal, sought to determine how cannabis inhal …

The study used positron emission tomography to show that men may have a greater number of CB1-type cannabinoid receptors than women do. This interesting finding may help in designing future studies regarding the health impact of cannabis in men and wom …

This study examined the anti-anxiety effect of cannabidiol using the Simulated Public Speaking Test to induce anxiety and the Visual Analogue Mood Scale to assess subjective ratings of anxiety. The authors also sought to identify the optimal dose of ca …

Five Cannabis Research Trends to Watch in 2023

Researchers continue to improve agricultural, production, and delivery techniques and study whether cannabinoids can help treat medical conditions.

Morgana Moretti, PhD, is an active scientist and freelance medical writer with more than 12 years of research and writing experience. She holds a doctoral degree in biochemistry, has published...

Cannabis research has increased in recent years as more territories have legalized the use of marijuana for medical and recreational purposes. The increase in legal access has led to a corresponding increase in scientific interest, with researchers eager to study cannabis's potential uses and effects. 

From improved cultivation practices to new delivery systems for cannabis-based medicines, this article explores the latest and most promising cannabis research trends. 

1. Modern cultivation and production techniques 

As the cannabis industry’s revenue increases, more companies invest in modern cultivation techniques and controlled agricultural practices. This includes developing and using advanced growing systems such as hydroponics and aeroponics and applying genetic engineering to create new strains with specific desired characteristics.

Research interest in sustainability and ethics is also growing, partly fueled by consumer education and news coverage of the topic. Precision irrigation methods, the development of biologically derived pesticide products, energy efficiency, and closed-loop cannabis extraction systems are active areas of research to minimize the environmental impact of cannabis production. 

As more stakeholders discuss the need for cannabis standards, the focus on standardization and quality control in cannabis cultivation continues to grow. This includes the use of Good Agricultural Practices, Good Manufacturing Practices, regular testing, and personnel training to ensure consistent and safe products.

"Obtaining products of good quality for medical research involves a careful selection of suppliers," says Juliana Bastos, PhD, a medical scientific specialist at Ease Labs, a group focused on developing, producing, and distributing natural products, including Pharmaceutical Standard Medical Cannabis. "There are many products on the market, and reliance on quality pharmaceutical products is interesting not only for academic purposes but will bring security for physicians and patients."  

2. Increasing focus on the therapeutic potential of cannabidiol 

Cannabidiol (CBD) is a non-psychoactive compound found in the cannabis plant. Unlike tetrahydrocannabinol (THC), the primary psychoactive compound in cannabis, CBD does not produce a "high" and has gained significant attention in cannabis research. Animal studies and human research suggest that CBD may help with depression, anxiety, post-traumatic stress disorder, Alzheimer's disease, and pain. 

CBD has also gained attention as a possible treatment for substance use disorder. A study published in 2022 identified 13 ongoing clinical trials intended to evaluate the efficacy of CBD to treat drug addiction. Conditions assessed in those studies included cannabis use disorder (five studies), opioid use disorder (four studies), alcohol use disorder (three studies), and cocaine use disorder (one study).

Considering the potential beneficial effects of CBD on human health, more research needs to be conducted to ensure its safety and efficacy. This includes the development of quality assurance standards for testing, which is currently a research gap. In addition, the development of high CBD, low THC cannabis strains through molecular breeding holds promise to accelerate cannabis research progress. 

3. Minor cannabinoids taking center stage

In addition to the major phytocannabinoids, THC and CBD, cannabis produces smaller amounts of more than 120 other cannabinoids. The phytocannabinoids present in smaller amounts in the cannabis plant are referred to as minor (or rare) cannabinoids and include cannabinol (a derivative of THC) and cannabigerol (the precursor of CBD). 

Minor cannabinoids have not been studied as extensively as CBD or THC. Still, recent research has shown potential therapeutic benefits for conditions such as neuropathic pain, neurodegenerative diseases, epilepsy, cancer, and skin disorders.

The results from preliminary research look promising, but much of the current knowledge of the medicinal benefits of minor cannabinoids has come from small studies rather than rigorous clinical trials. "Despite the popularity of cannabis products, many claims about their efficacy still need to be shown in large clinical trials," explains Bastos. "Knowing their mechanism of action and how minor cannabinoids interact with other medications is also important before claiming their therapeutic properties." 

Aligned with this trend, the National Center for Complementary and Integrative Health (NCCIH), issued a Notice of Special Interest aiming to promote mechanistic research of therapeutic benefits of minor cannabinoids and terpenes in cannabis. As researchers deepen their understanding of the cannabis plant and its compounds, we will likely better understand the health benefits of minor cannabinoids and how they could be applicable in the pharmaceutical industry.

4. New and improved delivery systems for cannabis-based medicines

A significant challenge in developing cannabis-based medicines is finding effective ways to deliver active compounds to the body. Traditional methods of ingestion, such as smoking, can harm people’s health and may not provide consistent dosing. Moreover, low aqueous solubility and poor bioavailability hinder the effective clinical development of oral cannabinoid formulations.

Academic researchers and pharmaceutical companies are exploring new delivery methods to make cannabis products more effective and safer. For example, sublingual formulations containing cannabinoids have been designed to be sprayed under the tongue and absorbed through the mucous membranes in the mouth, allowing for quick and efficient absorption into the bloodstream. 

The use of nanotechnology to deliver cannabis-based medicines is another promising research topic. Sosnik et al. (2021) showed the potential of polymeric nanocarriers for the ocular drug delivery of CBD, and Aphios Corporation will use the nanoencapsulation technique in a phase II study assessing the efficacy, safety, and tolerability of CBD as a pharmacotherapy for opioid dependence.

Transdermal patches , which allow for the slow release of active compounds through the skin, are also gaining popularity as cannabinoid delivery systems. This modality avoids the first-pass metabolism and leads to constant cannabinoid plasma levels.

The development of improved methods to deliver cannabis-based medicines is an active area of research and holds enormous potential for future treatments.

5. Cannabis research expands due to changes in the legal landscape 

On December 2, 2022, US president Joe Biden signed The Medical Marijuana and Cannabidiol Research Expansion Act , a federal policy breakthrough that removed many barriers to cannabis research. 

Before the new law, researching marijuana was challenging in the US as scientists needed approval from multiple agencies, which could sometimes take years.

Despite marijuana's continued classification as a Schedule I substance, the new legislation facilitates trials and development of new FDA-approved drugs that use marijuana or CBD. This is a significant step toward understanding cannabis's medicinal properties and potential therapeutic uses.

"Any act which improves cannabinoids research is relevant, mainly after the years of prohibition," says Bastos. Though this is a historic first step to facilitate cannabis research, more needs to happen within government and regulatory agencies to improve safety and access in the medical cannabis community. 

Researchers, clinicians, and regulatory officials must collaborate to ensure that phytocannabinoid products meet necessary therapeutic and safety standards. This can be achieved by:

• Conducting well-designed clinical trials
• Establishing guidelines for the production, labeling, and testing of cannabis
• Creating systems to monitor and report adverse events
• Collaborating on the development of education and information resources

By taking these steps, regulators and practitioners ensure that patients can access safe and effective phytocannabinoid products while protecting the public’s health.

Chromatography in Cannabis Testing

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Is cannabis today really much more potent than 50 years ago?

Levels of the psychoactive compound THC have been steadily rising in marijuana since the 1970s, due largely to growers selecting for more potent strains

By Alexis Wnuk

11 October 2023

Cannabis has become much more potent in recent decades

Soru Epotok/Shutterstock

Weed isn’t like it used to be. The psychoactive potency of cannabis is on the rise, which means that so too are the risks of potentially harmful side effects. With a growing acceptance of the drug around the world, as well as legalisation in many countries and US states, regulators are asking one question with increasing urgency: just how much stronger is today’s cannabis?

There is no way to comprehensively assess all types of cannabis currently available either legally or illegally around the world. But the data we have suggest that today’s drug is much stronger than the weed of even a few years ago, let alone several decades prior.

In the US, some of the most extensive research on cannabis strength comes from the Potency Monitoring Program, a project led by the National Institute on Drug Abuse and carried out at the University of Mississippi. The data shows a clear trend: over the last 50 years, the average amount of tetrahydrocannabinol (THC) in cannabis – the plant’s main psychoactive component – has increased more than tenfold.

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The uptick isn’t limited to the US. A study from 2020 examined marijuana potency trends in the US, the UK, the Netherlands, France, Denmark and New Zealand and found that average THC concentrations increased by 0.29 per cent each year from 1970 to 2017.

Over the years, growers have adopted increasingly sophisticated breeding techniques that have enabled them to select for more potent strains.

“If you talk to someone who’s been a cannabis user… the joke that they’ll make is that you can’t get the regular stuff anymore,” says Ryan Sultan at Columbia University in New York.

Take seedless cannabis, for instance, also known as sinsemilla. These unpollinated female plants are cultivated because their buds and flowers contain a lot of THC-rich resin – seedless cannabis can contain twice as much as the regular seeded variety. In 1993, this highly potent marijuana accounted for less than 4 per cent of all cannabis samples analysed by the Potency Monitoring Program, but by 2008 nearly half of the samples were sinsemilla.

Those data come from investigating drugs seized by the police, however, which might not cover the full range of cannabis people actually consume. What’s more, the number of seizures available for study vary widely from year to year: in 1972 there were just 34, while in 1995 there were more than 3700.

Yet another factor at play is that the way we consume cannabis has been shifting. While dried flower generally remains the most common form in which people consume weed , edibles, vapes and other forms have been growing in popularity – and these can be far easier to cram full of THC. Some concentrates have THC levels of up to 90 per cent , for instance.

The availability of highly potent marijuana – coupled with data showing that more and more people think cannabis is relatively harmless – is giving some researchers pause. Higher THC levels raise the risk of unpleasant or dangerous side effects like nausea, vomiting, paranoia and abnormal heart rhythms.

People point to the fact that humans have been smoking cannabis for thousands of years as evidence of its safety, says Sultan. But the strains available today can be so much stronger that we are in uncharted territory, he says.

The science of cannabis

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March 1, 2024

Is Marijuana Bad for Health? Here’s What We Know So Far

Marijuana’s health impacts—good and bad—are coming into focus

By Jesse Greenspan

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With decades of legal and social opprobrium fading fast, marijuana has become an extremely popular commercial product with more than 48 million users across the U.S. Health concerns, once exaggerated, now often seem to be downplayed or overlooked. For example, pregnant patients “often tell me they had no idea there's any risk,” says University of Utah obstetrician Torri Metz, lead author of a recent paper in the Journal of the American Medical Association on cannabis and adverse pregnancy outcomes.

Fortunately, legal reforms are also gradually making it easier to study marijuana's health effects by giving U.S. scientists more access to the drug and a wider population of users to study. Although much research remains in “early stages,” the number of studies has finally been increasing, says Tiffany Sanchez, an environmental health scientist at Columbia University. As new results accumulate, they offer a long-overdue update on what science really knows about the drug.

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In addition to minor side effects that many users joke about—such as short-term memory loss—recent studies have linked marijuana to adverse health outcomes involving the lungs, heart, brain and gonads. For example, heavy marijuana consumption seems to increase the risk of clogged arteries and heart failure , and it may impact male fertility . Smoking weed likewise can lead to chronic bronchitis and other respiratory ailments (although, unlike tobacco, it hasn't been definitively tied to lung cancer). And cannabis plants hyperaccumulate metal pollutants, such as lead, which Sanchez found can enter users' bloodstreams .

Developing adolescent brains, particularly those predisposed to mental illness, may be most at risk from overconsumption. Although psychiatric effects are hotly debated , studies suggest that heavy weed use exacerbates—or may trigger— schizophrenia , psychosis and depression in youths and that it affects behavior and academic performance. “From a safety viewpoint, young people should definitely stay away from it,” says University of Ottawa psychiatrist Marco Solmi, lead author of a recent review of cannabis and health in the British Medical Journal .

24 states have legalized recreational marijuana, with 38 allowing medical use

Moreover, the drug can cross over to fetuses during pregnancy. Several studies have linked it to low birth weights , and researchers suspect it raises the likelihood of neonatal intensive care unit admissions and stillbirths . Some cannabis dispensaries have advertised their products as a cure for morning sickness, but Metz emphasizes that safer alternatives exist.

Of course, many adults use marijuana responsibly for pleasure and relaxation. Unlike with, say, opioids, there's effectively zero risk of life-threatening overdose. Plus, “people get addicted with tobacco way faster,” says Columbia University epidemiologist Silvia Martins, who studies substance use and related laws.

Cannabis, and its derivatives, also may help alleviate pain—although some researchers contend that it performs little better than a placebo . It may also decrease chemotherapy-induced nausea, calm epileptic seizures , ease the symptoms of multiple sclerosis and serve as a sleep aid .

Recent studies have hinted that the drug might slightly reduce opioid dependency rates, although this, too, is disputed . There's some evidence that weed users tend to be more empathetic , and researchers found that elderly mice get a mental boost from the drug. Still, experts caution against self-medicating: “You should ask your doctor,” Solmi says.

Some of the recent research into marijuana is more lighthearted. One study, for instance, found that, just like people, nematode worms dosed with cannabis get the munchies .

Marijuana and Your Health: What 20 Years of Research Reveals

People who drive under the influence of marijuana double their risk of being in a car crash, and about one in 10 daily marijuana users becomes dependent on the drug, according to a new review.

Marijuana use has become increasingly prevalent over the years, and the review of marijuana studies summarizes what researchers have learned about the drug's effects on human health and general well-being over the past two decades.

In the review, author Wayne Hall, a professor and director of the Center for Youth Substance Abuse Research at the University of Queensland in Australia, examined scientific evidence on marijuana's health effects between 1993 and 2013.

He found that adolescents who use cannabis regularly are about twice as likely as their nonuser peers to drop out of school, as well as experience cognitive impairment and psychoses as adults. Moreover, studies have also linked regular cannabis use in adolescence with the use of other illicit drugs, according to the review, published today (Oct. 6) in the journal Addiction.

Researchers in the studies still debated whether regular marijuana use might actually lead to the use of other drugs, Hall wrote in the study. However, he pointed to longer-term studies and studies of twins in which one used marijuana and the other did not as particularly strong evidence that regular cannabis use may lead to the use of other illicit drugs. [ Marijuana vs. Alcohol: Which Is Worse for Your Health? ]

The risk of a person suffering a fatal overdose from marijuana is "extremely small," and there are no reports of fatal overdoses in the scientific literature, according to the review. However, there have been case reports of deaths from heart problems in seemingly otherwise healthy young men after they smoked marijuana, the report said.

"The perception that cannabis is a safe drug is a mistaken reaction to a past history of exaggeration of its health risks," Hall told Live Science.

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However, he added that marijuana "is not as harmful as other illicit drugs such as amphetamine, cocaine and heroin, with which it is classified under the law in many countries, including the USA."

The risks of using marijuana

Marijuana use carries some of the same risks as alcohol use, such as an increased risk of accidents, dependence and psychosis, he said.

It's likely that middle-age people who smoke marijuana regularly are at an increased risk of experiencing a heart attack , according to the report. However, the drug's "effects on respiratory function and respiratory cancer remain unclear, because most cannabis smokers have smoked or still smoke tobacco," Hall wrote in the review.

Regular cannabis users also double their risk of experiencing psychotic symptoms and disorders such as disordered thinking, hallucinations and delusions — from about seven in 1,000 cases among nonusers to 14 in 1,000 among regular marijuana users, the review said. And, in a study of more than 50,000 young men in Sweden, those who had used marijuana 10 or more times by age 18 were about two times more likely to be diagnosed with schizophrenia within the next 15 years than those who had not used the drug.

Critics argue that other variables besides marijuana use may be at work in the increased risk of mental health problems, and that it's possible that people with mental health problems are more likely to use marijuana to begin with, Hall wrote in the review.

However, other studies have since attempted to sort out the findings, he wrote, citing a 27-year follow-up of the Swedish cohort, in which researchers found "a dose–response relationship between frequency of cannabis use at age 18 and risk of schizophrenia during the whole follow-up period."

In the same study, the investigators estimated that 13 percent of schizophrenia cases diagnosed in the study "could be averted if all cannabis use had been prevented in the cohort," Hall reported.

As for the effects of cannabis use in pregnant women, the drug may slightly reduce the birth weight of the baby, according to the review.

The effects of euphoria that cannabis users seek from the drug come primarily from its psychoactive ingredient, called delta-9-tetrahydrocannabinol, better known as THC , Hall wrote in the review. During the past 30 years, the THC content of marijuana in the United States has jumped from less than 2 percent in 1980 to 8.5 percent in 2006.

The THC content of the drug has also likely increased in other developed countries, Hall wrote in the report.

It is not clear, however, whether increased THC content may have an effect on users' health, the report said. [ The Drug Talk: 7 New Tips for Today's Parents ]

Some argue that there would be no increase in harm, if users adjusted their doses of the drug and used less of the more potent cannabis products to get the same psychological effects they seek, Hall said.

However, "the limited evidence suggests that users do not completely adjust dose for potency, and so probably get larger doses of THC than used to be the case," Hall said.

Studies on the use of alcohol — and, to a lesser extent, other drugs such as opioids — have also shown that more potent forms of these substances increase users' level of intoxication, as well as their risk of accidents and developing dependence, he added.

Follow Agata Blaszczak-Boxe on  Twitter .   Follow Live Science @livescience , Facebook   & Google+ . Originally published on Live Science .

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Marijuana use linked to higher risk of heart attack and stroke

By American Heart Association News

Using cannabis – either by smoking, eating or vaping it – may raise the risk for heart attacks and strokes, new research suggests.

Survey respondents who said they use cannabis, or marijuana, had a higher risk for cardiovascular problems regardless of whether they used tobacco products or had other underlying cardiovascular risk factors, the study found. The research was published Wednesday in the Journal of the American Heart Association.

"Despite common use, little is known about the risks of cannabis use and, in particular, the cardiovascular disease risks," lead study author Dr. Abra Jeffers said in a news release . Jeffers is a data analyst at Massachusetts General Hospital in Boston. "The perceptions of the harmfulness of smoking cannabis are decreasing, and people have not considered cannabis use dangerous to their health."

In addition, she said, "smoking cannabis – the predominant method of use – may pose additional risks because particulate matter is inhaled."

The number of people using marijuana has increased significantly in recent decades in the U.S., where its recreational use has been legalized in 24 states and the District of Columbia. In 2019, a federal survey showed more than 48 million people ages 12 and older reported using marijuana at least once ­– nearly double the number in 2002. On the federal level, marijuana use remains illegal.

Prior research on the link between marijuana use and heart attacks or strokes has been limited for several reasons. The number of people who smoke marijuana frequently is relatively low, most studies have been done in younger populations that are at low risk for cardiovascular disease, and many people who use marijuana also use tobacco products, making it difficult to look at the effects of marijuana independently.

In the new study, researchers analyzed survey data from the Centers for Disease Control and Prevention for 434,104 U.S. adults from 2016 to 2020. They investigated whether the number of days of cannabis use in the past 30 days was associated with self-reported cardiovascular outcomes, including coronary heart disease, heart attacks and strokes, among the general adult population and people who had never smoked tobacco or used e-cigarettes. Researchers also investigated these associations among men under 55 and women under 65 who were at risk for heart disease.

Any marijuana use was linked to a higher risk for heart attacks and strokes, but people who used it most frequently had the highest odds. Adults who used marijuana daily had 25% higher odds of having a heart attack and 42% higher odds of stroke than people who didn't use it at all. Smoking was the most common method of cannabis use, followed by eating or vaping it.

Among men under 55 and women under 65, using marijuana resulted in a 36% higher combined odds for coronary heart disease, heart attack or stroke, regardless of whether they also used tobacco products. The odds were higher even when researchers looked only at those who had never used tobacco products or e-cigarettes.

"Cannabis smoke is not all that different from tobacco smoke, except for the psychoactive drug: THC versus nicotine," Jeffers said. "Our study shows that smoking cannabis has significant cardiovascular risks, just like smoking tobacco. This is particularly important because cannabis use is increasing, and conventional tobacco use is decreasing."

Dr. Robert L. Page II, who chaired the writing group for a 2020 American Heart Association scientific statement on marijuana's effects on cardiovascular health, said in the release that the new findings should be a "call to action for all practitioners" about "a potentially hazardous combination." Page is a professor of clinical pharmacy, medicine and physical medicine at the Skaggs School of Pharmacy and Pharmaceutical Sciences at the University of Colorado School of Medicine in Aurora. He was not involved in the new study.

"As cannabis use continues to grow in legality and access across the U.S., practitioners and clinicians need to remember to assess cannabis use at each patient encounter in order to have a nonjudgmental, shared decision conversation about potential cardiovascular risks and ways to reduce those risks," Page said.

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Marijuana linked to mental health risks in young adults, growing evidence shows

Over the last decade of diagnosing countless young patients with new psychotic disorders, one striking result has stuck out for New York City psychiatrist Dr. Ryan Sultan.

“Of all the people I’ve diagnosed with a psychotic disorder,” he said, “I can’t think of a single one who wasn’t also positive for cannabis.” 

Sultan, an assistant professor of clinical psychiatry at Columbia Irving Medical Center, is one of many experts raising serious concerns about the increasing marijuana use by adolescents and young adults.

And the evidence is growing of marijuana’s association with psychiatric disorders such as depression, bipolar disorder and schizophrenia, especially in young men. 

New research published this month, involving millions of people worldwide over decades, is adding to worries that heavy use of high-potency cannabis and legalization of recreational weed in many U.S. states could exacerbate the nation's mental health crisis in young adults.

“There is a big sense of urgency not just because more people are smoking marijuana, but because more people are using it in ways that are harmful, with higher and higher concentration of THC,” Dr. Nora Volkow, director of the National Institute on Drug Abuse (NIDA), said in an interview. 

One of the studies, from researchers in Denmark in collaboration with the U.S. National Institutes of Health, found evidence of an association between cannabis use disorder and schizophrenia. The finding was most striking in young men ages 21-30, but was also seen in women of the same age. 

The paper, published in the journal Psychological Medicine, looked at data from almost 7 million men and women in Denmark over the course of a few decades to look for a link between schizophrenia and cannabis use disorder . 

The magnitude of the connection between cannabis and schizophrenia for young men surprised study author Volkow, who was expecting the number to be closer to 10%.

“This is worrisome,” she said. 

There are now 22 states that allow recreational use of marijuana, with Minnesota likely to become the next state to legalize it. 

Whether recreational cannabis laws contribute to underage consumption is unclear, but Volkow has made addressing cannabis use among teenagers one of NIDA’s top priorities. Daily marijuana use among young adults has risen to record highs, with more than 1 in 10 of young adults ages 19-30 now reporting daily use, and almost half reporting use within the last year, according to the agency's most recent data.

Another study , led by Sultan and Columbia researchers published earlier this month, found that teenagers who use cannabis only recreationally are two to four times more likely to develop psychiatric disorders, including  depression and suicidality, than teenagers who don’t use cannabis at all.

Because research to date has been observational and doesn’t directly prove cause and effect, the connection between marijuana and psychiatric disorders is controversial. It’s unclear whether people who already have or are developing psychiatric conditions are more likely to turn to cannabis as a way to self-medicate or whether cannabis use triggers mental problems.

Volkow is optimistic that a large ongoing study on adolescent brain development at the National Institutes of Health can help answer this question.

Sultan acknowledged the limitations of the evidence. “It’s sort of this circular feedback where they’re kind of just feeding off each other,” he said. 

Dr. Deepak D’Souza, a psychiatrist at Yale University who has been studying cannabis for 20 years, insists there are too many lines of evidence to ignore. 

“We may be grossly underestimating the potential risks associated with cannabis,” he said. 

Given increasing legalization and rising potency in cannabis products, D’Souza has never been more worried about the mental health effects of cannabis use among youth.

“This is a massive concern,” he said. “We have been woefully inept in educating the public and influencing policy.” 

Is legalization affecting rates of marijuana use?

Early data suggests that in young adults ages 18-25, legalization is leading to higher rates of cannabis use, particularly in Oregon and Washington, according to an analysis published earlier this month in the journal Substance Abuse.

The research, led by researchers from McMaster University in Canada, found the evidence in other age groups a little less clear, and more research is needed to understand how legalization is affecting rates of cannabis use.  

In areas where marijuana becomes legal and easier to access, Volkow’s concern is the ease with which products can be mixed, leading to a high total dose of marijuana consumed. 

One of the biggest issues, she says, is the lack of regulation on the concentration of THC in products.

Marijuana consumed decades ago had concentrations of THC, the main psychoactive ingredient, of 2 to 3%, but cannabis products today can have THC levels as high as 90%.

“That’s not even the case for alcohol as you cannot put more than a certain percent alcohol into liquor,” she said. “The same thing with tobacco cigarettes, you regulate how much nicotine they have. Here, we have no regulation.”

THC potency is significant, Volkow said, because cannabis is more likely to be linked to psychosis with higher doses consumed. 

What age is the most vulnerable?

Research has shown that the human brain is the last organ to fully develop and doesn’t finish until the mid-to-late 20s. That makes adolescents and young adults particularly vulnerable to the effects of cannabis as their brains continue to mature. 

“Really, the ideal time to consider using weed — if you’re going to use it — is 26 or later,” Sultan said. 

People who wait until at least age 26 are much less likely to become addicted or develop mental disorders, said Dr. Sharon Levy, a pediatrician and addiction specialist at Boston Children’s Hospital. 

“The greatest risks are clearly in the adolescent and young adult age range,” she said.

However, people with a family history of a psychotic disorder shouldn’t use cannabis at all, Sultan cautioned

What does cannabis do to the brain?

Although scientists are still learning about the effects of marijuana on developing brains, studies so far suggest marijuana use in teenagers may affect functions such as attention, memory and learning , multiple studies have found.

“It’s somehow interfering with the connections that we use in our brain to distinguish between what’s going on in our heads and what’s going on outside of our heads,” Levy said in reference to the psychotic symptoms that can happen. 

D’Souza added that cannabis use can have serious impacts on the developing brain because of its effects on the endocannabinoid system, a complex signaling system in the brain that marijuana targets. 

“Endocannabinoid systems play an important role in sculpting the brain during adolescence, which is when schizophrenia usually manifests itself,” he said.

Disturbing that system with cannabis use could have “far reaching complex implications on brain development.” 

Akshay Syal, M.D., is a medical fellow with the NBC News Health and Medical Unit. 

More From Forbes

9 out of 10 americans support legalizing marijuana, new poll finds.

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Nearly 9 out of 10 Americans believe that marijuana should be legal in the United States, according to the findings of a new public opinion poll. The survey by the Pew Research Center, which was released by the firm on Thursday, found that 88% of respondents said that cannabis should be legal for medical or recreational use by adults.

The poll found that a strong majority (57%) of Americans said they believe that weed should be legal for recreational and medical purposes, while less than a third (32%) said that marijuana should be legal for medical use only. Only 11% of those polled said that cannabis should not be legal for any purpose.

Impacts Of Legalizing Recreational Pot

The results of the new poll and previous surveys show that opinions about marijuana legalization have remained fairly constant over the past five years. However, the new research also revealed that Americans have split opinions on the impact of legalizing recreational marijuana.

A new Pew Research Center poll shows that 88% of Americans support legalizing marijuana for ... [+] recreational or medicinal purposes.

Just over half (52%) said that legalizing the use of recreational marijuana is good for local economies, while only 17% said it is bad. Nearly three out of 10 (29%) said that legalizing recreational weed has no impact on local economies.

About four out of 10 (42%) respondents said that legalizing recreational marijuana, also referred to as adult-use cannabis, makes the criminal justice system more fair, while a similar number (38%) said the reform has no impact on fairness. Less than one in five (19%) said that legalizing recreational marijuana makes the justice system less fair.

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Similar to previous polls, the new survey found that young adults aged 18-29 showed the strongest support for ending the prohibition on marijuana, with 71% saying recreational weed should be legal. Among adults aged 30-49, 62% said recreational cannabis should be legalized. Half (50%) of adults aged 50-64 and 65-74 said pot should be legal for all adults, while less than a third (31%) of those aged 75 and up said the same.

Democrats were most supportive of cannabis policy reforms, with nearly three-quarters (72%) saying pot should be legal for both medical and recreational purposes. By contrast, only 42% of those who identified as Republicans said they believe adult-use cannabis and medical marijuana should be legalized.

The poll also found other differences in Americans’ views on the effect of legalizing recreational. While 29% said it increases the use of other drugs such as heroin, fentanyl and cocaine, a similar percentage (27%) said that legalizing recreational pot reduces the use of other recreational drugs. Just over four out of 10 said the move does not impact the use of other drugs. Republicans were more likely to believe this debunked “gateway drug” theory, with 42% of GOP voters saying legalizing recreational marijuana increases the use of other drugs while only 17% of Democrats said the same.

Progress On Marijuana Legalization Continues

The results of the new poll come as the number of states that have legalized marijuana continues to grow. So far, 24 states have legalized cannabis for all adults and 38 have legalized medical marijuana. Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws, noted that no state has backtracked on legalizing recreational pot after taking the step.

“There’s no ‘buyer’s remorse’ among the public when it comes to legalizing cannabis,” NORML’s deputy director Paul Armentano said in a statement from the group after the results of the latest Pew Research marijuana poll were released. “As more states have adopted legalization, public support for this policy has risen dramatically. That’s because these policies are largely working as intended and because voters prefer legalization and regulation over the failed policy of cannabis prohibition. Elected officials who refuse to take action to end cannabis criminalization do so at their own political peril.”

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Most americans favor legalizing marijuana for medical, recreational use, legalizing recreational marijuana viewed as good for local economies; mixed views of impact on drug use, community safety.

Pew Research Center conducted this study to understand the public’s views about the legalization of marijuana in the United States. For this analysis, we surveyed 5,140 adults from Jan. 16 to Jan. 21, 2024. Everyone who took part in this survey is a member of the Center’s American Trends Panel (ATP), an online survey panel that is recruited through national, random sampling of residential addresses. This way nearly all U.S. adults have a chance of selection. The survey is weighted to be representative of the U.S. adult population by gender, race, ethnicity, partisan affiliation, education and other categories. Read more about the ATP’s methodology .

Here are the questions used for the report and its methodology .

As more states pass laws legalizing marijuana for recreational use , Americans continue to favor legalization of both medical and recreational use of the drug.

An overwhelming share of U.S. adults (88%) say marijuana should be legal for medical or recreational use.

Nearly six-in-ten Americans (57%) say that marijuana should be legal for medical and recreational purposes, while roughly a third (32%) say that marijuana should be legal for medical use only.

Just 11% of Americans say that the drug should not be legal at all.

Opinions about marijuana legalization have changed little over the past five years, according to the Pew Research Center survey, conducted Jan. 16-21, 2024, among 5,14o adults.

The impact of legalizing marijuana for recreational use

While a majority of Americans continue to say marijuana should be legal , there are varying views about the impacts of recreational legalization.

About half of Americans (52%) say that legalizing the recreational use of marijuana is good for local economies; just 17% think it is bad and 29% say it has no impact.

More adults also say legalizing marijuana for recreational use makes the criminal justice system more fair (42%) than less fair (18%); 38% say it has no impact.

However, Americans have mixed views on the impact of legalizing marijuana for recreational use on:

• Use of other drugs: About as many say it increases (29%) as say it decreases (27%) the use of other drugs, like heroin, fentanyl and cocaine (42% say it has no impact).
• Community safety: More Americans say legalizing recreational marijuana makes communities less safe (34%) than say it makes them safer (21%); 44% say it has no impact.

Partisan differences on impact of recreational use of marijuana

There are deep partisan divisions regarding the impact of marijuana legalization for recreational use.

Majorities of Democrats and Democratic-leaning independents say legalizing recreational marijuana is good for local economies (64% say this) and makes the criminal justice system fairer (58%).

Fewer Republicans and Republican leaners say legalization for recreational use has a positive effect on local economies (41%) and the criminal justice system (27%).

Republicans are more likely than Democrats to cite downsides from legalizing recreational marijuana:

• 42% of Republicans say it increases the use of other drugs, like heroin, fentanyl and cocaine, compared with just 17% of Democrats.
• 48% of Republicans say it makes communities less safe, more than double the share of Democrats (21%) who say this.

Demographic, partisan differences in views of marijuana legalization

Sizable age and partisan differences persist on the issue of marijuana legalization though small shares of adults across demographic groups are completely opposed to it.

Older adults are far less likely than younger adults to favor marijuana legalization.

This is particularly the case among adults ages 75 and older: 31% say marijuana should be legal for both medical and recreational use.

By comparison, half of adults between the ages of 65 and 74 say marijuana should be legal for medical and recreational use, and larger shares in younger age groups say the same.

Republicans continue to be less supportive than Democrats of legalizing marijuana for both legal and recreational use: 42% of Republicans favor legalizing marijuana for both purposes, compared with 72% of Democrats.

There continue to be ideological differences within each party:

• 34% of conservative Republicans say marijuana should be legal for medical and recreational use, compared with a 57% majority of moderate and liberal Republicans.
• 62% of conservative and moderate Democrats say marijuana should be legal for medical and recreational use, while an overwhelming majority of liberal Democrats (84%) say this.

Views of marijuana legalization vary by age within both parties

Along with differences by party and age, there are also age differences within each party on the issue.

A 57% majority of Republicans ages 18 to 29 favor making marijuana legal for medical and recreational use, compared with 52% among those ages 30 to 49 and much smaller shares of older Republicans.

Still, wide majorities of Republicans in all age groups favor legalizing marijuana at least for medical use. Among those ages 65 and older, just 20% say marijuana should not be legal even for medical purposes.

While majorities of Democrats across all age groups support legalizing marijuana for medical and recreational use, older Democrats are less likely to say this.

About half of Democrats ages 75 and older (53%) say marijuana should be legal for both purposes, but much larger shares of younger Democrats say the same (including 81% of Democrats ages 18 to 29). Still, only 7% of Democrats ages 65 and older think marijuana should not be legalized even for medical use, similar to the share of all other Democrats who say this.

Views of the effects of legalizing recreational marijuana among racial and ethnic groups

Substantial shares of Americans across racial and ethnic groups say when marijuana is legal for recreational use, it has a more positive than negative impact on the economy and criminal justice system.

About half of White (52%), Black (53%) and Hispanic (51%) adults say legalizing recreational marijuana is good for local economies. A slightly smaller share of Asian adults (46%) say the same.

Criminal justice

Across racial and ethnic groups, about four-in-ten say that recreational marijuana being legal makes the criminal justice system fairer, with smaller shares saying it would make it less fair.

However, there are wider racial differences on questions regarding the impact of recreational marijuana on the use of other drugs and the safety of communities.

Use of other drugs

Nearly half of Black adults (48%) say recreational marijuana legalization doesn’t have an effect on the use of drugs like heroin, fentanyl and cocaine. Another 32% in this group say it decreases the use of these drugs and 18% say it increases their use.

In contrast, Hispanic adults are slightly more likely to say legal marijuana increases the use of these other drugs (39%) than to say it decreases this use (30%); 29% say it has no impact.

Among White adults, the balance of opinion is mixed: 28% say marijuana legalization increases the use of other drugs and 25% say it decreases their use (45% say it has no impact). Views among Asian adults are also mixed, though a smaller share (31%) say legalization has no impact on the use of other drugs.

Community safety

Hispanic and Asian adults also are more likely to say marijuana’s legalization makes communities less safe: 41% of Hispanic adults and 46% of Asian adults say this, compared with 34% of White adults and 24% of Black adults.

Wide age gap on views of impact of legalizing recreational marijuana

Young Americans view the legalization of marijuana for recreational use in more positive terms compared with their older counterparts.

Clear majorities of adults under 30 say it is good for local economies (71%) and that it makes the criminal justice system fairer (59%).

By comparison, a third of Americans ages 65 and older say legalizing the recreational use of marijuana is good for local economies; about as many (32%) say it makes the criminal justice system more fair.

There also are sizable differences in opinion by age about how legalizing recreational marijuana affects the use of other drugs and the safety of communities.

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Table of contents, most americans now live in a legal marijuana state – and most have at least one dispensary in their county, 7 facts about americans and marijuana, americans overwhelmingly say marijuana should be legal for medical or recreational use, clear majorities of black americans favor marijuana legalization, easing of criminal penalties, religious americans are less likely to endorse legal marijuana for recreational use, most popular.

About Pew Research Center Pew Research Center is a nonpartisan fact tank that informs the public about the issues, attitudes and trends shaping the world. It conducts public opinion polling, demographic research, media content analysis and other empirical social science research. Pew Research Center does not take policy positions. It is a subsidiary of The Pew Charitable Trusts .

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• MIND, BODY, WONDER

Do you smoke weed recreationally? Here's what experts want you to know.

Today’s cannabis strains are not your grandma’s weed—and they may be impacting your mental health, heart health, and more.

Some 23 states and the District of Columbia have legalized recreational cannabis in recent years, and others, including Florida, will vote to do so in November. This changing landscape has led to a dramatic rise in consumption, with some 62 million Americans using cannabis in 2023. But legalization of cannabis doesn’t mean that regular consumption is completely safe.

A growing body of evidence has documented an array of health concerns beyond just dry mouth and fatigue and includes both mental and physical illnesses. One recent study even links cannabis consumption to heart disease .

“People think about Bob Marley when they think about cannabis. They think it’s natural, it’s Mother Nature, that it’s not going to do any harm,” says Marco Solmi, a psychiatrist at the University of Ottawa. Yet his review of the substance published in the BMJ found numerous potential problems .

Cannabis isn’t dangerous in the same way opioids are, says Deborah Hasin, an epidemiologist at Columbia University who has researched cannabis use and abuse. “People don’t die from cannabis overdose,” she says. “But it can have a lot of other consequences to both physical and psychological health.”

Stronger strains abound

Some of the problems can be attributed to the stronger strains now available . As Maria Rahmandar, medical director of the substance use and prevention program at Chicago’s Lurie Children’s Hospital, put it at a recent discussion of cannabis at the National Academies of Sciences, Engineering, and Medicine, today’s products are “not your grandmother’s weed.”

“These products are much more potent and come in so many different formulations, that it’s very different from those in the sixties and even the nineties,” Rahmandar says.

The way people consume cannabis today increases the amount of the active ingredient, tetrahydrocannabinol (THC), they ingest. Vaping and edibles generally deliver higher quantities than rolling and smoking joints does, Rahmandar says.

Psychological distress a significant problem

One of the lesser-known but troublesome risks of regular cannabis use is substance-abuse psychosis, where a person has delusions or paranoia, hears voices, and otherwise temporarily loses touch with reality. The psychosis generally resolves within a few days, but in some cases requires hospitalization.

This condition can occur with any psychologically altering substances, but the risk from cannabis is higher even than from cocaine, Solmi says.

“You’re more likely to develop substance-abuse psychosis if you use cannabis daily, but I cannot tell you there’s a safe amount that would prevent this,” he says. Young adults and males are the most prone.

Especially worrisome, up to a third of people who experience substance-abuse psychosis go on to develop the more permanent condition of schizophrenia, Solmi says.

( Schizophrenia in women is widely misunderstood—and misdiagnosed )

Observational studies also connect other mental-health conditions to frequent cannabis use. Solmi’s review found that depression increases, as does violence among dating couples. And since cannabis causes cognitive impairment—as well as visual impairment—car accidents have risen among users who drive while under the influence.

Experts especially worry about the mental health impacts for teenagers. Some 17 percent of tenth graders report using cannabis, even though no state has legalized the drug for anyone under 21.

Adolescents are 37 percent more likely to develop depression by young adulthood if they regularly use cannabis compared to non-users. Rates of suicide are also higher.

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“Teenage brains are going through a time of maturity and pruning, so when substances are put in there, they have more of an influence than they do on adult brains,” Rahmandar says.

Cannabis harms the heart

Regular use of cannabis can also lead to significant physical problems.

People who use the drug regularly have a higher risk for heart attack, stroke, and other heart disease , according to a large population-based study published in the Journal of the American Heart Association in February. Heart attack rates rose 25 percent while stroke increased 42 percent in this group, the researchers found.

This likely occurs because THC affects blood flow in the arteries and because receptors for cannabinoids exist throughout the cardiovascular system, the authors state. People who smoke their weed also boost their heart disease risk from the particulate matter they inhale alongside the THC.

Other studies have linked cannabis with improving nausea and vomiting after chemotherapy, but the BMJ   review found regular users can actually suffer from an extended vomiting condition known as hyperemesis. “This is rare, but it’s increasing as more people use the drug,” Hasin says.

Pregnant women who use cannabis regularly are more likely to have preterm births and dangerously small babies. More research is needed to determine whether this results from the drug itself or from other lifestyle factors among those who choose to use cannabis while they are pregnant, Solmi says.

Cannabis addiction is a concern

Many people perceive cannabis to be safer than alcohol, but one in five cannabis users develop an addiction to the drug. Symptoms of cannabis use disorder are like those for other substances.

“If people experience cravings, feel they need more and more to get the same effects, they’ve had unsuccessful attempts to quit or cut down,” or have any of several other symptoms “that’s a warning,” Hasin says.

As with alcohol, cannabis addiction can lead to personal, financial, legal, and health problems .

Certain groups are at particularly heightened risk for this addiction. Rates in veterans have increased substantially since 2005, Hasin found in her research. She attributes this to a combination of increased potency and greater acceptance of the drug from its legal status, as well as the likely use of cannabis to self-medicate chronic pain and psychiatric disorders. “The VA has done a good job of reducing unnecessary prescribing of opioids in veterans, so some of them might be turning to cannabis,” she says.

( Is pain relief from cannabis all in your head? )

Young people are also at risk for developing this disorder. Youth who begin using the drug at earlier ages or who have a family history of addiction especially heighten their odds for trouble .

“People younger than 25 should avoid cannabis altogether,” Solmi says. “They have no idea how they will react to cannabis. You’re gambling with your brain and your health.”

For everyone else, moderation is key.

“This isn’t a benign substance that has no risk,” Rahmandar says. “Most users will be fine, but we can’t predict who will develop problems.”

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March 30, 2024

This article has been reviewed according to Science X's editorial process and policies . Editors have highlighted the following attributes while ensuring the content's credibility:

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Germany's legal weed sparks calls to protect young people

Smoking weed will soon be legal for over-18s in Germany, but addiction experts are calling for more prevention efforts to ensure young people are protected from the dangers of cannabis use.

Under one of the most liberal drug laws in Europe, adults in Germany will from April 1 be allowed to carry up to 25 grams of dried cannabis on them and cultivate up to three marijuana plants at home.

"From our point of view, the law as it is written is a disaster," Katja Seidel, a therapist at a drug addiction center in Berlin, told AFP.

"Access to the product will be easier, its image will change and become more normalized, especially among young people ," Seidel said, adding that she expects to see an increase in cannabis use "at least initially".

The government says decriminalizing weed will hit the black market and reduce the spread of contaminated cannabis.

Health Minister Karl Lauterbach, a physician himself, acknowledges cannabis can be "dangerous" especially for people under the age of 25 whose brains are still developing.

Medical experts say cannabis use among young people can affect the development of the central nervous system, leading to an increased risk of developing psychosis and schizophrenia.

Lauterbach has promised a major campaign to educate youngsters about the health risks and boost prevention programs, but it remains unclear how much money the government plans to spend and how effective it will be.

The new legislation has some safeguards to protect young people, including a ban on smoking cannabis within 100 meters (328 feet) of a school, kindergarten, playground or sports center.

Reaching young people

Seidel, who works at the Tannenhof Berlin-Brandenburg drug rehabilitation organization, is one of just two staff members who visits schools in the capital and surrounding areas to talk to young people about drug addiction and prevention.

To reach all pupils in the region, "at least 10 employees" would be needed, she told AFP.

The Addiction Prevention Center in Berlin, run by the local authorities, also wants more resources poured into raising awareness.

It shouldn't be the case that students learn about the dangers of cannabis consumption "just by chance", said Janis Schneider, who works for the center.

Health Minister Lauterbach has promised that the government's campaign will explain, for example, "that children and young people who start smoking weed are much less likely to graduate from high school".

The federal center for health education , linked to the health ministry, told AFP it will "assume its responsibility by expanding its prevention offers".

The planned media campaign however hasn't convinced critics. "It doesn't resonate with them, it will never work," said Boris Knoblich, a spokesman for the Tannenhof Berlin-Brandenburg organization.

"What works is someone who goes in, talks to them over a coffee, without a teacher there," he said.

The southern state of Bavaria meanwhile is testing an online training course for teachers on how to approach the topic in the classroom.

Prevention kits

In Berlin, staff from the Tannenhof organization bring a prevention "kit" with them on their school visits: a green suitcase emblazoned with a cannabis leaf. It contains information sheets, games and material for activities.

Students are asked to insert colored balls into two tubes that represent arguments for and against cannabis use, resulting in a visual representation of the cons outweighing the pros in the long term.

"We spend at least three hours with them in a relaxed atmosphere. This allows students not to self-censor," said Pascal Noack from Tannenhof Berlin-Brandenburg.

According to official statistics from 2021, 8.8 percent of adults in Germany aged 18-64 admitted to consuming cannabis at least once in the preceding 12 months.. Among people aged 12-17, that number rose to nearly 10 percent.

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Low-income California Latinos at higher risk from Parkinson’s-linked weedkiller

Analysis finds majority of paraquat, banned in 60 countries, is used in counties where Latinos make up 75% of the population or higher

Low-income Latinos living in California are disproportionately threatened by paraquat, a highly toxic herbicide widely used on US cropland, a new analysis of state data finds.

The notorious weedkiller is banned in more than 60 countries and for some uses in the US, like golf courses, because it is so dangerous. But the US government still allows its use on crops, putting agricultural workers or those living in communities near where it is spread at risk.

Most of the paraquat sprayed in California is used in five counties with a Latino population of 75% or higher, and poverty rates of at least 20%, the first-of-its-kind analysis, conducted by the Environmental Working Group (EWG) non-profit, found. It reframes the debate around paraquat in environmental justice terms.

“We were shocked when we saw, in particular, how these five communities are disproportionately exposed, and are disproportionately Latino and poor,” said Scott Faber, EWG’s policy director.

Paraquat is linked to non-Hodgkin lymphoma, respiratory damage and kidney disease, and ingestion of a single teaspoon is considered deadly. The Environmental Protection Agency (EPA) has ignored a “mountain of evidence” showing the substance causes Parkinson’s disease, said Alexander Rabine, the analysis’s author. That includes an epidemiological study of central California farming communities that clearly showed an increased risk of Parkinson’s.

Research has found the substance interferes with dopamine production and regulation, and people with Parkinson’s have reduced dopamine levels. Still, the EPA has resisted banning it in the US.

EWG’s analysis looked at data from California because it is the only state with readily available paraquat figures – it found about 80% of the substance was spread in Latino-majority census tracts between 2017 and 2021. Nearly all of California’s farm workers are Latino, federal data shows.

Overall, 5.3m lb of paraquat were sprayed in California, the analysis found, though its use was concentrated in central counties that produce fruit and nut crops, like almonds, grapes, pistachios, alfalfa, cotton, walnuts and pomegranates.

In one of those counties, Kern, home to Bakersfield, EWG found 1.2m lb were spread across about 1,200 sq miles of farmland. The county’s poverty rate is nearly 30%.

“No one should be exposed to pesticides at that level,” Rabine said.

The substance is especially pernicious because it stays in the dirt or moves through the air and harms people living nearby, including agricultural workers and their families. Research has found those living within a third of a mile of where the chemical is sprayed are twice as likely to develop Parkinson’s, EWG noted. Workers also get the chemicals on their clothes and bring it into their homes, where children, who are especially vulnerable, can be exposed.

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Outside of California, the herbicide is widely used in Iowa and the Mississippi River valley. Federal law requires the EPA to consider pesticides’ economic benefit before enacting restrictions, and an agency analysis “concluded that these [health] risks were outweighed by the benefits of the use of paraquat”.

The EPA also states that the labels provide specific instructions on how to safely apply paraquat, but public health advocates say farmers often do not follow the directions, do not provide adequate protection for workers, and pressure workers into cutting corners.

An ongoing federal lawsuit brought by public health groups asks a court to order paraquat off the market, but states can also ban it, Faber said.

“What’s clear is so long as the EPA is ignoring the links between paraquat and Parkinson’s, and giving greater weight to the needs of farmers than the needs of farm workers, then it will be up to California to act,” Faber said.

• Income inequality
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What’s Going on With Legal Marijuana in New York?

Get up to speed on the state’s nascent cannabis industry with the New York Times reporter who covers it.

By Terence McGinley

Times Insider explains who we are and what we do and delivers behind-the-scenes insights into how our journalism comes together.

In New York, the recreational cannabis market hasn’t quite taken off as planned.

It’s been three years since New York legalized marijuana, and the state has awarded few licenses to applicants who want to open cannabis businesses. Today, illicit head shops far outnumber licensed dispensaries. So this month, Gov. Kathy Hochul ordered a review of the state’s Office of Cannabis Management, with the goal of speeding up its licensing bureaucracy.

Ashley Southall was covering criminal justice and policing in New York when she lobbied her editors to establish a beat for cannabis in 2022. Since then, she has observed, as she recently wrote, the “fits and starts” of a legal industry trying to take root in one of the world’s largest markets for cannabis .

In an interview, she explained how New York has fallen short of its goals and why the state hopes it can still build a successful market. This conversation has been edited.

Gov. Hochul said the rollout of legal cannabis in New York was “a disaster.” What, in her eyes, has been so disastrous?

There are a few things the governor mentions when she talks about why the program is a disaster. The biggest thing is the proliferation of illicit shops that have jumped the line to open. There are over 2,000 rogue shops in New York City, and about only 85 licensed dispensaries statewide. There are many more unlicensed shops than there are legal places to buy safe, tested weed, which sends tax revenue toward repairing some of the harm of the war on drugs. The state is still trying to figure out how to achieve those central goals of the legalization law.

New York City residents are familiar with the smoke shops that have proliferated in the past 12 to 18 months. Why have these shops been able to open?

For years, New York has had a problem with empty real estate. You can go down streets in the city and see empty storefronts where a bank or a cafe used to be. When legalization passed, there was a sort of cash grab, and landlords began renting to unlicensed sellers. At the time, there wasn’t a lot of clarity about their legal status because there weren’t regulations. The Office of Cannabis Management had not been set up. By the time the state clarified that these shops were illegal because they were not licensed, a lot of stores were already open. Enforcement didn’t follow.

Unlicensed store owners see an opportunity to make money; they also don’t face strong punishment. The fines that the state issues can be contested, and they’re not stiff enough to make business owners think twice. One of the things that the city and the state have tried to do is to put pressure on landlords to evict these stores. So far, that hasn’t been effective.

So there’s no law enforcement agency that can raid an unlicensed store and shut it down?

That’s what the New York City Sheriff’s Office does every day. But after a raid, many of these stores just reopen within a matter of hours or days. Even after a raid, there’s still a process of administrative hearings. The city or state has to make its case and meet evidentiary goals. The stores fight back and say, “We’re not selling weed, we’re selling hemp,” to get around the cannabis law. It can take a while to get a court order that puts a padlock on stores, which is what the state is really seeking. They’re seeking to get them out of business.

Enforcement against unlicensed vendors was not part of legalization law because the people writing it did not anticipate these rogue shops cropping up. So one of the things that held up enforcement as unlicensed shops were multiplying was the need to sort out who was ultimately responsible. That was assigned to the state cannabis and tax agencies, but their resources are limited. So lawmakers now want to give more power to local authorities. It’s high on the agenda of current budget negotiations.

Since legalizing cannabis at the end of 2012, Washington State has seen relative success in that most consumers purchase legal weed. In California, the illicit market is still thriving six years after legalization. Does New York think it’s possible to get on the path of Washington State?

The state has got to get a handle on these shops. You can’t have illegal shops competing with licensed retailers because they’re going to undercut licensed retailers at every turn, especially on price.

But the state also has to change consumer sentiment. A lot of consumers either don’t know or don’t care that many of these shops are unlicensed. They don’t understand why the difference is important. The state has to get the message out that cannabis legalization is not just about a cash grab by the government, but about addressing some of the harms of the war on drugs through tax revenues, which unlicensed shops are not paying.

What should consumers know about the differences between purchasing cannabis at a licensed dispensary versus an unlicensed shop?

At licensed dispensaries, you pay an extra 13 percent for cannabis, and that goes back to state and local governments to invest in education and drug treatment. Some goes to policing, but the largest portion goes toward programs that support people who are affected by the war on drugs. It could be job training, education or housing for people with criminal drug convictions.

A lot of illicit weed is coming from out of state. Some of it is grown legally, but it failed testing, or it hasn’t been tested at all. Some of the products are counterfeit and may be tainted with copper or lead. So there’s a health aspect to this as well.

Where is marijuana legal in the US? A state-by-state guide

Recreational marijuana is currently legal in 24 states and Washington, D.C. Another 17 states have legalized the use of marijuana solely for medical purposes, with varying caveats in each state's laws.

By Kyla Russell • Published March 26, 2024 • Updated on March 27, 2024 at 7:23 am

A decade after Colorado and Washington state approved cannabis for recreational use, prohibitions have fallen across the country as an overwhelming share of U.S. adults support legalization of the drug.

Federally, marijuana is still classified as a Schedule I drug, alongside heroin and LSD, and can carry criminal penalties for possession. Last summer however, the Health and Human Services Department suggested the federal government move marijuana to the less tightly regulated Schedule III list. The Drug Enforcement Administration, which has the final say, said it will take up the issue. Documents released earlier this year show FDA scientists have concluded marijuana is not as prone to abuse as other tightly controlled substances and has potential medical benefits.

President Joe Biden has issued pardons to thousands of people for federal marijuana possession and commuted long sentences handed down for nonviolent drug offenses. In 2022, he urged governors to pardon state offenses

We're making it easier for you to find stories that matter with our new newsletter — The 4Front. Sign up here and get news that is important for you to your inbox.

Meanwhile, here's where each state stands on the issue: 

States where marijuana is fully legal 

Alaska : Adults over the age of 21 can legally use and possess up to an ounce of marijuana recreationally, though it is still illegal to consume in public and punishable by a fine of up to $100. Adults may also cultivate up to six marijuana plants in a household, but only three of the plants can be mature. 

Arizona : Adults 21 and over can use, possess and buy up to 1 ounce of marijuana of which not more than 5 grams of that allowable ounce can be marijuana concentrates. Medical card holders can posses more than twice that amount. However, smoking or vaping marijuana in public remains illegal. Adults 21 and older can legally cultivate up to six plants in a home.

California : Adults over the age of 21 can legally buy and posses 1 ounce of cannabis or up to 8 grams of concentrated cannabis for recreational use. For medicinal use with a physician's prescription, the age drops to 18 and users have higher possession limits. The sale of cannabis is legal at licensed dispensaries and adults can grow up to six cannabis plants at home, though rules on cultivating requirements vary by cities and counties. Marijuana use in public spaces remains illegal.

Colorado : Residents over the age of 21 can buy up to 1 ounce of marijuana, 8 grams of marijuana concentrate or marijuana products containing up to 800 milligrams of THC in a single transaction. The law limits possession to 2 ounces of "retail" marijuana, purchased from a licensed dispensary.

Connecticut : Adults over the age of 21 are allowed to possess or consume up to 1.5 ounces (42.5 grams) of “cannabis plant material” and up to 5 ounces (141.7 grams) in a locked container in a home or in the trunk or locked glove box in the person’s vehicle.

Delaware : People 21 and older can possess up to up to 1 ounce (28 grams) of leaf marijuana, 12 grams of concentrated marijuana, or marijuana products containing up to 750 milligrams of the psychoactive compound THC. Possession of more than an ounce of marijuana and public consumption would remain misdemeanors.

Illinois : Residents over the age of 21 may purchase and possess up to 1 ounce of marijuana at any time. Non-residents may have 15 grams. However, consuming it in public places remains illegal.

Maine : In Maine, anyone over 21 can possess up to 2.5 ounces (70.9 grams) of marijuana. An adult can also cultivate up to three flowering marijuana plants and 12 immature plants.

Maryland : In Maryland, people 21 and older can possess up to 1.5 ounces of cannabis flower, 12 grams of concentrated cannabis or a total amount of cannabis products that does not exceed 750 mg THC

Massachusetts : Adults over the age of 21 possession of up to 1 ounce of marijuana outside the home and up to 10 ounces inside their homes. If you're caught with more than 2 ounces of marijuana outside the home, it's a criminal offense. Residents may also grow up to six plants per person and up to 12 plants per household, but not in public view. However, landlords may prohibit tenets from growing pot plants.

Michigan : Michigan residents who are 21 or older can possess or transport up to 2.5 ounces (70.8 grams) of marijuana. They can grow up to 12 plants, although not in public view. They also can give 2.5 ounces (70.8 grams) to another person, but not for payment

Minnesota : Adults 21 and older can possess and travel in the state with 2 ounces of cannabis flower, 8 grams of concentrate and 800 milligrams worth of THC-containing edible products such as gummies and seltzers. They can have up to 2 pounds of cannabis flower at home.

Missouri : Adults 21 and older can purchase and posses 3 ounces of marijuana. Medical patients are allowed to buy 6 ounces per 30-day period. Residents may also have up to six flowering plants at home, but are required to register for a cultivation card through the state's health department. The cost of the card is $100.

Montana : Adults 21 and older can buy and possess an ounce of cannabis, up to 8 grams of concentrate or edibles containing up to 800 mg of THC — the main psychoactive compound in cannabis. But adult-use marijuana businesses are not allowed in counties where the majority of voters rejected the recreational marijuana ballot measure that passed in 2020.

Nevada : Anyone who is over 21 with a valid ID can buy up to an ounce of pot or one-eighth of an ounce of edibles or concentrates. People can only use the drug in a private home as it remains illegal to consume it in public, except for at licenses businesses with established on-site consumption lounges. Residents can grow six plants a person, and 12 plants per household.

New Jersey : Dispensaries are allowed to sell up to the equivalent of 1 ounce of cannabis, which means an ounce of dried flower, or 5 grams of concentrate or 1,000 milligrams of edibles, like gummies to adults 21 and older. The state decriminalized possession of 6 ounces (170 grams) or less of marijuana or about three-fifths of an ounce (17 grams) of hashish.

New Mexico : In April 2021, New Mexico Gov. Michelle Lujan Grisham signed a bill allowing adults over the age of 21 to have up to two ounces of cannabis with them to grow up to six cannabis plants per person, or 12 per household. 

New York : Anyone 21 and over can buy and possess up to 3 ounces of cannabis or 24 grams of concentrated forms of the drug, such as oils. Individual adults may also grow up to six cannabis plants — three mature and three immature — in their home for personal use and up to 12 plants for a household.

Ohio : Adults 21 and over can buy and possess up to 2.5 ounces of cannabis and to grow up to six plants per individual or 12 plants per household at home.

Oregon : Adults over the age of 21can possess up to eight ounces of marijuana in their home and up to one ounce away from home. For edible products, the limits are 16 ounces for a solid form and 72 ounces for drinkables. Residents can grow up to four cannabis plants in the house. Consuming marijuana in public remains illegal.

Rhode Island : Anyone 21 and older can buy and possess up to 1 ounce of cannabis with no more than 10 ounces (283 grams) for personal use kept at a person’s home. Resident may also grow up to six plants, with no more than three mature, at home.

Vermont : Adults over the age of 21 can buy and possess up to 1 ounce of marijuana, two mature and four immature plants.

Virginia : Anyone over the age of 21 can possess up to an 1 ounce of cannabis and grow up to four plants for personal use. The plants cannot be in public view. 

Washington : Adults 21 and older can buy up to an ounce of dried marijuana, 16 ounces of pot-infused solids, 72 ounces of pot-infused liquids or 7 grams of concentrated marijuana, like hashish.

Washington, D.C . : Adults over the age of 21 can possess up to 2 ounces of marijuana and can may gift up to 1 ounce to another person as long as "nothing else of value changes hand." That because while recreational marijuana has been legalized in D.C., it's still illegal to buy and sell the drug. Adults can legally grow up to six marijuana plants, but only three of them can be mature. 

US Health Dept. recommends easing federal restrictions on Marijuana

Can You Bring Weed on a Plane? It's Complicated

States that have legalized medical marijuana.

Alabama : The medical marijuana program will allow resident who are 19 and older — or under 19 with guardian permission — with one of 16 qualifying medical conditions, to purchase medical marijuana with the recommendation of a doctor. Among the qualifying conditions for treatment are cancer-related nausea or vomiting, or chronic pain; Crohn’s disease; depression; epilepsy, HIV/AIDS-related nausea or weight loss; panic disorder, Parkinson’s disease; persistent nausea; post-traumatic stress disorder; sickle cell anemia; spasticity associated with multiple sclerosis, spinal cord injury and Tourette’s syndrome. Marijuana would allow marijuana in forms such as pills, skin patches and creams, but not smoking or vaping products. *** Medical marijuana remains unavailable in Alabama more than two years after lawmakers voted to legalize it in 2021. The state had to develop rules, and the selection process has been bogged down in disputes.

Arkansas : Patients over 18 with a qualifying medical condition or verified caregivers in the state of Arkansas can possess up to 2.5 ounces of cannabis to be used for medical purposes only. To purchase, a state-issued medical marijuana ID card is needed. Patients or caregivers can apply for an ID with a physician written certification and a state ID. 

Florida : Residents who are 18 and older and have one of 12 qualifying medical conditions may a medical marijuana card from a licensed physicians. Physicians cannot issue a certification for more than three 70-day supply limits of marijuana or more than six 35-day supply limits of marijuana in a form for smoking, and a 35-day supply for smokable marijuana must be 2.5 ounces or less.

Hawaii : Patients and caregivers may purchase up to 4 ounces of marijuana from a dispensary and cultivate up to 10 plants at home. However, patients must register as a cultivator with the state before growing their plants. For in-state residents, patients must be 18 and older, have one of 15 qualifying conditions and possess a medical marijuana card. Out-of-state visitors can also register to get medical cannabis while visiting Hawaii. Those patients can apply online for a 60 day registration card and pay a $49.50 fee in order to shop at Hawaii’s dispensaries.

Iowa : Patients over the age of 18, with an eligible condition can obtain a state-issued medical marijuana card. With their card, a patient can purchase 4.5 grams of THC every 90 days.

Louisiana : Medical marijuana is legal in Louisiana with a verified medical card that indicates a recommendation from a registered physician. Patients must be at least 18 years old and sales are capped at 2.5 ounces every 14 days.

Mississippi : Card-carrying patients over 18 years old can buy up to 3.5 grams of cannabis flower or 1 gram of cannabis concentrate per day from a licensed dispensary, but no more than 24 days in a month. Minors with permission from a custodial parent or legal guardian may obtain a card through a physician. However, residents with prior convictions may not qualify for the program

New Hampshire : Patients who are 18 years of age and old, with a valid registry card can buy up to 2 ounces of marijuana at a time. Purchases are also capped at 2 ounces in a 10-day period. 

North Dakota : Medical marijuana is legal in the state for patients over 19 years old with one of 31 qualifying conditions. Anyone purchasing either flower or topical products are subject to monthly limits: no more than 2.5 ounces at a time and no more than 6,000 milligrams of THC in topicals or concentrates.

Oklahoma : Any patient over 18 years old with a medical marijuana card can posses up to 8 ounces of marijuana in their home, up to an ounce of concentrated marijuana, up to 72 ounces of edible marijuana and to three ounces of marijuana on their person.  They can also cultivate up to six plants.

Pennsylvania : Residents 18 years and older with one of 23 qualifying medical conditions can apply for a medical marijuana ID card. Exact dosage limits are not inscribed in the law. Patients are capped at a 90-day supply determined by the recommending doctor.

South Dakota : Patients over the age of 18 with a "debilitating medical condition" can apply for a state-issued medical marijuana card. The card fee is $75 and carriers can use it to buy up 3 ounces of cannabis flower every 14 days. They can also register to obtain permission to cultivate up to two cannabis flowering plants and two cannabis plants that are not flowering.  

Utah : Resident over the age of 21with one of more than a dozen qualifying medical conditions may be referred to for a medical marijuana card, which costs $15 and requires renewal every 6-months. A one-month supply in accordance with the dosage amount specified by a doctor or state-licensed pharmacist can be acquired at a time or up to 4 ounces of cannabis flower or 20 grams of THC. However, sparking up is still illegal in the state, as are edibles. Medical cannabis can be consumed via vaping, tablets, capsules and oils, among other forms.

West Virginia : Patients over 18 years old with one of 15 qualifying conditions can get a state-issued medical marijuana ID card and purchase cannabis in the form of pills, oils, gels, creams, ointments, tinctures, liquid, and non-whole plant forms for administration through vaporization. Dispensaries cannot sell edibles and smoking marijuana remains prohibited. Exact dosage limits are not inscribed in the law. Patients are limited to a 30-day supply at a time, determined by the recommending doctor.

*** Kentucky : Last year, lawmakers gave the green light for the state to launch a medical marijuana program in 2025. However, marijuana remains illegal in the state. Patients with a diagnosis from the list of 21 approved conditions can possess up to 8 ounces of marijuana. That marijuana must come from a state where it's legal.

*** Georgia : Patients with a doctor's approval can receive a medical marijuana card for a variety of conditions, however the state's medical cannabis program is limited to low-THC, which the minimal amount of tetrahydrocannabinol (THC), typically less than 0.3%. Qualified patients can possess up to 20 fluid ounces of low-THC oil. A medical marijuana card costs $25.

*** Texas : Medical cannabis is legal in Texas in very limited circumstances. Patients with certain qualifying medical conditions can obtain cannabis oil with less than 1% THC by weight. They can also obtain CBD products. Other forms of marijuana for consumption, like smoking, vaping and edibles remain illegal.

States where marijuana is still illegal

Idaho : The use of marijuana for medical or recreational purposes remains fully illegal in Idaho. Possessing more than 3 ounces of marijuana can be punished with a prison sentence of up to five years and a fine of up to $10,000, or both. Under 3 ounces is a misdemeanor offense that carries a fine.

Indiana : Possession of any amount of marijuana is a crime in Indiana, but anything less than 30 grams is treated as a misdemeanor offense. Anything over 30 grams is a Class D felony resulting in jail time and fines. 

Kansas : All forms and amounts of marijuana are illegal in Kansas. First time offenders caught with any amount of marijuana faces a fine of up to $1,000 and a maximum of 6 months in prison. However, Kansas law if very severe toward repeat offenders, with second time charges doubling jail time and increased fines.

Nebraska : Anyone caught with less than 1 ounce marijuana, regardless of the THC percentage, and it is your first offense, you can be charged with an infraction which carries a maximum fine of $300. However, possession of possession of more than an ounce carries jail time and fines.

North Carolina : Marijuana in North Carolina is fully illegal, and punishable by varying amounts of prison time and fines, depending on the amount in your possession.

South Carolina : Marijuana is also fully illegal in South Carolina, with the potential penalties of jail time and fines depending of the amount the accused possessed.

Tennessee : Marijuana remains fully illegal in Tennessee. Possession of any amount will lead to jail time and fines, with length of incarceration and penalties depending on the amount.

Wisconsin : Marijuana in Wisconsin is fully illegal and punishable prison time and fines, which vary depending on the amount in your possession.

Wyoming : Any use of marijuana is illegal in Wyoming. Any person caught using or under the influences marijuana is subject to jail time and/or fines.

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