Teen Cannabis Use Doubles Risk of Psychotic and Bipolar Disorders by Adulthood

A large-scale study has found that teenagers who use cannabis face double the risk of developing psychotic or bipolar disorders by early adulthood. The research tracked nearly half a million young people over a decade, linking even occasional cannabis use to serious mental health problems later in life. Funded by the US National Institute on Drug Abuse, the findings add to growing concerns about the drug's long-term effects on young brains.

The study followed 463,396 individuals from adolescence into their mid-20s, using electronic health records from routine paediatric visits between 2016 and 2023. Researchers found that any self-reported cannabis use between the ages of 13 and 17—regardless of frequency—raised the likelihood of psychotic or bipolar disorders by 100%. On average, psychiatric diagnoses appeared 1.7 to 2.3 years after the first recorded cannabis use.

The risk held firm even when accounting for other factors, such as pre-existing mental health conditions or the use of other substances. Adolescents covered by Medicaid or living in poorer neighbourhoods were more likely to report cannabis use, suggesting socioeconomic factors may play a role in exposure.

Meanwhile, the potency of legal cannabis in the US has surged since 2000. THC levels, once around 4%, now average 15–20% in many products, with some exceeding 30%. States like California, Colorado, and Oregon report the highest concentrations, driven by selective breeding and advanced growing techniques. This rise in potency could further amplify risks for young users.

The research provides strong evidence that adolescent cannabis exposure is a potential risk factor for later mental illness. With THC levels in legal products continuing to climb, health experts warn that early use may carry even greater dangers than previously understood. The findings underscore the need for targeted prevention efforts, particularly among vulnerable youth.