A landmark population study involving nearly half a million teenagers has found that adolescent marijuana use is associated with more than double the risk of developing two of the most serious mental illnesses known — psychotic disorders and bipolar disorder — by young adulthood.
The research, published in JAMA Health Forum on February 20, 2026, tracked 463,396 adolescents aged 13 to 17 through age 26 using electronic health record data from Kaiser Permanente Northern California. It represents one of the largest longitudinal studies of its kind ever conducted on adolescent cannabis use and psychiatric outcomes.
