This is one of the largest studies ever conducted on teen cannabis use and psychiatric outcomes, and it reinforces that age restrictions and youth prevention should be central to any legalization framework. A JAMA Health Forum study of 463,396 adolescents ages 13 to 17 found cannabis use was linked to a twofold increase in psychotic and bipolar disorder risk by age 26. The study represents one of the largest longitudinal investigations of this association, drawing on clinical health records rather than self-reported data.