Nearly half a million teens were tracked in this study, and the data shows cannabis use during adolescence meaningfully increases the chance of serious psychiatric diagnoses in early adulthood. A large longitudinal cohort study published in JAMA Health Forum tracked 463,396 adolescents and found that cannabis use between ages 13 and 17 was associated with approximately double the risk of psychotic and bipolar disorders by age 26. Elevated risks for depression and anxiety were also observed.