Adolescent Cannabis Use Doubles Risk of Psychotic and Bipolar Disorders

Cannabis is the most widely used illicit drug among U.S. adolescents. About 8% of 8th graders report using it, a figure that climbs to 26% by 12th grade. For years, researchers debated whether these numbers should prompt alarm or be treated as a rite of passage. A study published in JAMA Health Forum involving nearly half a million adolescents now adds substantial weight to the alarm side of that argument.

The research, a longitudinal analysis of 463,396 adolescents aged 13 to 17 tracked through age 26, found that past-year cannabis use was associated with a doubling in the risk of developing both psychotic and bipolar disorders. Associations with depressive and anxiety disorders were also statistically significant, though smaller in magnitude. The study drew on electronic health record data from routine pediatric visits between 2016 and 2023, collected through Kaiser Permanente in collaboration with the Public Health Institute, the University of California San Francisco, and the University of Southern California. Funding came from the National Institute on Drug Abuse.

Not Just Heavy Users

One of the study's most consequential design choices was its scope. Rather than focusing exclusively on cannabis use disorder or daily users, the researchers examined any self-reported past-year cannabis use, detected through universal screening at standard pediatric appointments. This matters because most prior studies concentrated on heavy or problematic use, potentially underestimating risk for the far larger population of occasional users. The current study captures that group.

Cannabis use preceded psychiatric diagnoses by an average of 1.7 to 2.3 years, a temporal sequence that strengthens the case for cannabis exposure as a potential risk factor rather than a byproduct of pre-existing mental illness. The team also controlled statistically for prior mental health conditions and other substance use, and the associations held.

"Even after accounting for prior mental health conditions and other substance use, adolescents who reported cannabis use had a substantially higher risk of developing psychiatric disorders - particularly psychotic and bipolar disorders," said Kelly Young-Wolff, PhD, lead author and senior research scientist at the Kaiser Permanente Division of Research.

THC Potency Has Changed the Equation

The cannabis today's teenagers encounter is categorically different from what previous generations used. Average THC levels in California cannabis flower now exceed 20%, compared to concentrations in the low single digits a few decades ago. Concentrates can exceed 95% THC. The implications for brain development during adolescence - a period characterized by ongoing neural pruning and heightened vulnerability to psychoactive substances - are not fully understood but potentially substantial.

The endocannabinoid system plays a critical role in brain maturation. THC disrupts this system by binding to cannabinoid receptors, with potentially lasting effects on neural circuits that govern mood, perception, and executive function. The dose-dependency of these effects, and whether the risk curve is linear or has thresholds, remains an open question the current study was not designed to answer.

Disparities Embedded in the Data

The study also found that cannabis use was more common among adolescents enrolled in Medicaid and those living in socioeconomically deprived neighborhoods. This pattern raises a separate concern: that expanding cannabis commercialization and marketing could widen existing mental health disparities, concentrating psychiatric risk in communities that already face structural disadvantages in accessing mental health care.

Lynn Silver, MD, program director of the Getting it Right from the Start program at the Public Health Institute and a study co-author, called for a public health response that would reduce product potency, prioritize prevention, and limit youth exposure and marketing. "The evidence increasingly points to the need for reducing product potency, prioritizing prevention, limiting youth exposure and marketing, and treating adolescent cannabis use as a serious health issue, not a benign behavior," Silver said.

What the Study Can and Cannot Tell Us

Observational studies of this design cannot establish causation. The observed associations, even controlling for prior conditions, may still reflect unmeasured confounders - genetic predispositions to both cannabis use and psychiatric illness, for example, or environmental factors correlated with both. This limitation is worth naming clearly.

Still, the study's longitudinal design, its large and clinically diverse sample, and its use of real-world screening data across a general adolescent population make it considerably more representative than smaller convenience studies. The consistency of the temporal sequence - use preceding diagnosis - adds credibility to the risk interpretation.

Young-Wolff emphasized that parents and clinicians need accurate, evidence-based information. The data now point to even modest cannabis use during the teen years as carrying meaningful psychiatric risk - a message that sits uncomfortably alongside the relaxed cultural and legal attitudes toward cannabis that have spread across much of the United States over the past decade.

With cannabis legalization expanding at the state level and marketing pressure intensifying, the public health calculus will need to weigh findings like these carefully. The adolescent brain is not the same as the adult brain. The gap between how cannabis is regulated and what the evidence says about adolescent risk is one that health authorities will increasingly have to address.