To make an impact on rising rates of depression and suicide in adolescents, we must improve our ability to predict when, why, and which individuals experience increases in depression and suicidal ideation. This study investigates how acute cannabis use and withdrawal affect short-term risk for depression and suicide ideation among adolescents. By analyzing time-varying patterns of substance use, mood, and suicide risk, the study aims to guide the development of scalable, accessible, and personalized interventions to reduce adolescent depression and suicide risk (NCT 06576076; R01 DA054145).