Teenagers who use cannabis face a substantially higher risk of developing serious psychiatric disorders in young adulthood, according to a large new study published in JAMA Health Forum. The research adds weight to long-standing concerns about how cannabis use may affect the developing brain.
Researchers analyzed health records from 463,396 adolescents aged 13 to 17 and followed them through age 26. Those who reported using cannabis within the previous year were significantly more likely to later be diagnosed with psychotic disorders, bipolar disorder, depression and anxiety.
Higher risks for psychosis and bipolar disorder
The study found that adolescent cannabis users had roughly double the risk of developing psychotic and bipolar disorders compared with non-users. These conditions are among the most severe mental illnesses and can require long-term treatment while affecting education, employment and other areas of everyday life.
Because researchers followed patients over several years, cannabis use was documented before the mental health diagnoses appeared. On average, cannabis use was recorded 1.7 to 2.3 years before a psychiatric disorder was first diagnosed, strengthening the case for a potential causal link.
Researchers adjusted their analyses for previous mental health problems and other substance use, yet the elevated risk remained. This suggests that cannabis may independently contribute to later psychiatric problems rather than simply being used by teenagers who are already struggling with their mental health.
Stronger products, wider availability
The research was led by scientists from Kaiser Permanente, the Public Health Institute, the University of California, San Francisco, and the University of Southern California, with funding from the U.S. National Institute on Drug Abuse. The authors highlight how rising cannabis potency may amplify potential risks.
In legal markets such as California, average THC concentrations in cannabis flower now exceed 20%, far higher than typical levels several decades ago. Concentrated products can contain more than 95% THC, raising concerns about how these stronger formulations may affect adolescent brains that are still developing.
Public health experts warn that aggressive marketing and the normalization of cannabis may obscure these risks. They argue that prevention campaigns need to keep pace with the rapid expansion of the legal cannabis industry and the increasing potency of many products available for sale.
Cannabis remains common among teens
Cannabis remains the most widely used illicit drug among U.S. adolescents. Federal survey data indicate that use rises sharply throughout the high school years, from about 8% of eighth graders to roughly 26% of twelfth graders reporting cannabis use during the previous year.
The 2024 National Survey on Drug Use and Health found that more than 10% of U.S. teenagers aged 12 to 17 had used cannabis during the previous year. This level of exposure, combined with increasingly potent products, has intensified concerns about possible long-term mental health consequences.
Unlike many earlier studies that focused primarily on heavy users or people with cannabis use disorder, the new study examined any self-reported cannabis use during the previous year. Even this broader measure was associated with increased risk, underscoring that potential harm may not be confined to the heaviest users.
Equity concerns and policy implications
The researchers also identified important disparities. Cannabis use was more common among adolescents covered by Medicaid and those living in socioeconomically disadvantaged neighborhoods, suggesting that commercialization could deepen existing mental health inequities.
Experts say these findings support stronger regulations on cannabis marketing and potency, particularly in states with legal recreational markets. They also call for improved screening in pediatric care, alongside clear, evidence-based communication about cannabis risks for parents and teenagers.
While the study does not prove that cannabis use alone causes mental illness, it adds to a growing body of evidence linking early cannabis use with lasting psychiatric risks. Clinicians and policymakers are increasingly urging a cautious approach to youth cannabis use as legalization continues to spread.
