IMPORTANCE: As cannabis becomes more accessible and socially accepted, concerns have grown about its potential implications for adolescent mental health. While prior research has linked adolescent cannabis use to psychiatric symptoms, few large, population-based, longitudinal studies have examined associations with clinically diagnosed psychiatric disorders.

OBJECTIVE: To evaluate whether adolescent cannabis use is associated with an increased risk of incident psychotic, bipolar, depressive, and anxiety disorders during adolescence and young adulthood.

DESIGN, SETTING, AND PARTICIPANTS: This cohort study included adolescents aged 13 to 17 years who were screened for past-year cannabis use at Kaiser Permanente Northern California from 2016 to 2023. Adolescents were followed up through age 25 years or until December 31, 2023. Data were analyzed from February 21, 2024, to August 27, 2025.

EXPOSURE: Time-varying self-reported past-year cannabis use based on universal, confidential screening during standard pediatric care.

MAIN OUTCOMES AND MEASURES: Incident clinician-diagnosed psychotic, bipolar, depressive, and anxiety disorders, which were identified through electronic health records using International Classification of Disease codes. Cox proportional hazards regression models were used to measure the strength of associations between adolescent cannabis use and incident psychiatric diagnoses, with adjustments for sex, race and ethnicity, neighborhood deprivation index, insurance type, and time-varying alcohol and other substance use.

RESULTS: Of 463 396 adolescents (234 114 males [50.5%]; mean [SD] age, 14.5 [1.3] years) included in the sample, 136 708 were Hispanic individuals (29.5%), 93 737 were non-Hispanic Asian individuals (20.2%), 35 346 were non-Hispanic Black individuals (7.6%), 153 102 were non-Hispanic White individuals (33.0%), and 18 795 individuals were multiracial or of other races or ethnicities (4.1%). At baseline, 26 345 adolescents (5.7%) self-reported past-year cannabis use. Past-year cannabis use was associated with an increased risk of incident psychotic (adjusted hazard ratio [AHR], 2.19; 95% CI, 1.97-2.42), bipolar (AHR, 2.01; 95% CI, 1.82-2.22), depressive (AHR, 1.34; 95% CI, 1.30-1.39), and anxiety disorders (AHR, 1.24; 95% CI, 1.21-1.28). The strength of the associations between cannabis use and incident depressive and anxiety disorders decreased as adolescents aged. This pattern was similar but slightly attenuated after additional adjustment for past psychiatric conditions (psychotic disorder: AHR, 1.92; 95% CI, 1.73-2.13; bipolar disorder: AHR, 1.73; 95% CI, 1.57-1.90; depressive disorder: AHR, 1.33; 95% CI, 1.29-1.38; anxiety disorder: AHR, 1.19; 95% CI, 1.16-1.23).

CONCLUSIONS AND RELEVANCE: This cohort study found that adolescent cannabis use was associated with increased risk of incident psychiatric disorders, particularly psychotic and bipolar disorders. These results could inform the development of clinical and educational interventions for parents, adolescents, and clinicians, as well as protective policies to prevent or delay adolescent cannabis use in the context of expanding cannabis legalization.