Teenagers Who Use Cannabis Face Sharply Higher Odds of Psychosis and Bipolar Disorder

The Question Legalization Forces to the Front

As cannabis legalization spreads across U.S. states and internationally, the policy debate has largely centered on adult use, criminal justice reform, and tax revenue. The question of what expanded access means for adolescents -- developmentally the group most vulnerable to cannabis's neurological effects -- has received less attention in the legal framework, even as the scientific literature on adolescent cannabis and psychiatric risk has grown steadily more concerning.

A cohort study published in JAMA Health Forum adds to that literature with one of the more comprehensive assessments of psychiatric outcome risk associated with adolescent cannabis use. The findings are relevant not only to parents, clinicians, and educators, but to policymakers designing the guardrails that accompany legalization.

What the Study Found

Adolescent cannabis use was associated with increased risk of incident psychiatric disorders across multiple categories. The associations were strongest for psychotic disorders and bipolar disorder -- conditions with particularly severe consequences for long-term function and quality of life. Elevated risks were also observed for depressive and anxiety disorders, though the relative increases were more modest for those conditions.

The cohort design -- following individuals over time to observe which outcomes developed -- is methodologically stronger than cross-sectional surveys that capture only a single time point. Cohort studies allow researchers to establish that cannabis use preceded the onset of psychiatric diagnosis rather than simply co-occurring with it, which matters for causal inference. That said, residual confounding from pre-existing vulnerabilities -- genetic risk factors, early-life adversity, or family mental health history -- remains a challenge in this type of research and cannot be fully excluded.

Context and Mechanism

The adolescent brain is not fully developed until the mid-20s. The prefrontal cortex, which regulates executive function, impulse control, and emotional processing, matures last. The endocannabinoid system -- the system that cannabis compounds target -- plays an active role in that developmental trajectory. Disruption of endocannabinoid signaling during adolescence may interfere with normal neural pruning and circuit formation in ways that increase vulnerability to psychiatric conditions, particularly for individuals with pre-existing genetic risk.

The risk is not uniform. Not every adolescent who uses cannabis develops a psychiatric disorder. Most do not. But the elevated relative risks documented in cohort studies like this one suggest that cannabis is not neurologically benign during adolescence, and that among the minority who do develop psychiatric consequences, the burden is severe.

Implications for Policy and Clinical Practice

The study's authors note that the findings could inform clinical and educational interventions aimed at parents, adolescents, and clinicians. Age-based restrictions in legalization frameworks -- rules that parallel minimum drinking age laws -- are the primary protective mechanism currently in place in most jurisdictions. Whether those restrictions are sufficient, and whether additional policies such as potency limits or targeted prevention programs for high-risk adolescents would reduce harm, are questions the data raise but do not definitively resolve.

The corresponding author is Kelly C. Young-Wolff, PhD, MPH, at Kaiser Permanente. Published in JAMA Health Forum (doi: 10.1001/jamahealthforum.2025.6839). Full author information, funding disclosures, and conflict-of-interest statements are available in the published article.