Calls to Reassess Cannabis Risks: New Research Reported

Many people think it’s impossible to become addicted to “weed.” Unfortunately, cannabis use disorder (CUD) is a rapidly growing addiction in the United States. In addition, evidence suggests a dose-response relationship, with more frequent use of higher-potency cannabis products associated with a greater risk of behavioral health problems in young people. Recent studies have highlighted numerous unintended consequences of cannabis legalization.

Recent Studies

A huge longitudinal study examined the impact of state-level medical and recreational cannabis laws on cannabis use disorder (CUD) and cannabis poisonings. The study included 110,256,536 enrollees. It showed states with legalized medical cannabis had a 42.7% increase in CUD and nearly double that increase in cannabis poisonings when compared to states without such laws.

In another study published in JAMA Network Open in 2025, individuals with an initial hospital-based encounter (emergency department visit or hospitalization) for CUD had nearly three times an increased risk of death within 5 years compared to the general population. This study analyzed data from nearly 12 million Canadian residents over 5 years. As with other substance use disorders (SUDs), a diagnosis of CUD increases death risks, although they are still lower than seen with alcohol, stimulant, or opioid use disorders.

Recently, Colorado, NIDA, and other researchers investigated the impact of cannabis use on cognitive functions, particularly working memory. This JAMA study examined 1,000+ adults ages 22-36 with brain imaging technology. Researchers found nearly two-thirds (63%) of heavy lifetime cannabis users exhibited reduced brain activity during working memory tasks, with 68% of recent users showing similar effects. This reduced activity was also linked to poorer performance in tasks requiring working memory, such as following instructions or solving problems. Cannabis may have effects that make learning and school performance challenging. Alarmingly, the authors concluded negative outcomes associated with heavy lifetime cannabis use and working memory in healthy young adults that may be long-lasting. However, it’s important to note while these studies indicate associations, establishing causation requires further research.

Another recent JAMA study in Canada showed the number of individuals with CUD requiring hospital care for their addiction increased by 270% after the legalization of non-medical cannabis. In addition, the percentage of new cases of schizophrenia receiving hospital care for a CUD before their schizophrenia diagnosis increased from 7% to 16%. Rising cases of psychosis underscore the urgent need for the prevention of teen and young adult use.

Laura Bierut, M.D. Alumni Endowed Professor of Psychiatry

Source: Washington University School of Medicine

A new 2025 JAMA editorial by Laura Bierut, M.D. emphasized escalating public health concerns posed by the rising prevalence of cannabis use disorder. It noted cannabis use in the U.S. has nearly doubled in the past decade. Said Beirut, “The facts are clear: cannabis is addictive, its use is on the rise, and those affected by cannabis use disorder face a heightened risk of premature death. It is time to confront this public health crisis head-on.”

Marijuana Use, Depression, and Suicide

The association between cannabis use and increased risks of depression and suicidality was recently highlighted. A 2024 study concluded cannabis use is linked with increased depressive and manic symptoms in the general population and an elevated likelihood of developing major depressive disorder (MDD) and bipolar disorder (BD). Self-medication with cannabis use apparently worsens response to treatment and prognosis.

A major Columbia University JAMA study concluded teens engaging in recreational cannabis use were 2-4 times more likely to develop psychiatric disorders, depression, and suicidality than non-using peers. Cannabis use and CUD alone, are related to the suicidality among young adults — with or without depression.

Déjà Vu All Over Again

The National Institute on Drug Abuse (NIDA) has expressed long-standing concerns about unintended consequences of cannabis legalization. NIDA has implemented initiatives to inform the public about potential risks associated with teen and young adult use, such as impaired driving, pregnancy, mental health disorders, and addiction. They have also informed clinicians and policymakers that medical/“prescribed” cannabis use does not lower the risk of dependency.

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Taking Cannabis Claims With a Grain of Salt

While my work in this area was mostly in showing the effects of secondhand marijuana smoke on the brain and behavior at the University of Florida's Brain Institute, I did write a 1989 book "Marijuana" which covered the pharmacology, neurobiology, and behavioral effects of marijuana, highlighting risks to teens, tolerance, withdrawal, and sometimes addiction concerns. I wrote "An entire generation of Americans grew up believing that marijuana was virtually risk-free. This belief persists, despite growing evidence of physical, psychological, and social harm that is caused by the drug. "

In my recent Addiction Policy Forum webinar with Morehouse University Chair Sarah Vinson, M.D., we discussed the complex relationship between cannabis use and adolescent development. The presentation explored the effects of cannabis on adolescent brain development, memory, and behavior, and risks for life-changing, long-term consequences.

I continue to strongly advocate for increased prevention, education, intervention, and CUD treatment efforts to mitigate elevated risks associated with early cannabis exposure.

Summary

Recent studies suggest the cannabis experiment, which essentially field-tested the safety of marijuana on the American public, is failing. Claims for medical efficacy are mostly unsubstantiated, while the consequences of widespread access and use are being reported by researchers around the world. THC doses, exposure consequences, and the development of CUDs have increased. THC levels have quadrupled since the 1990s. Risks increase with a high cannabis THC concentration and increased frequency of cannabis use. According to National Institute of Drug Abuse data, cannabis samples seized in 1995 averaged less than 4% THC. In 2022, they averaged more than 16%. Scientists reporting adverse effects and possibly irreversible effects on the brains and behavior of youths are becoming commonplace. Cannabinoids contribute to chronic psychotic events and schizophrenia, especially if taken during adolescence. Cannabis use should be regulated and discouraged, and prevention efforts should be strengthened, especially with reference to adolescence. The genie is out of the bottle… but we need to rethink protecting our most vulnerable and young people.