Psychosis Symptoms Increased Before Teens Started Using Cannabis, Not Just After

Adolescents who used cannabis at any point had more psychosis symptoms (B=0.86) and distress from symptoms (B=1.17) than never-users, consistent with shared vulnerability. Symptoms increased in the time leading up to cannabis initiation (B=0.16 for symptoms, B=0.23 for distress), consistent with self-medication. Evidence for post-initiation increases (contributing risk) was mixed.

Cohort study using 5 waves across 4 years from the ABCD Study (n=11,858 adolescents aged 9-10 at baseline). Discontinuous growth curve modeling assessed psychosis symptom trajectories before and after cannabis initiation, adjusting for age, sex, other substance use, SES, and parental mental health.

This is one of the most rigorous tests of the cannabis-psychosis causal question. By modeling symptom trajectories before and after cannabis initiation, it provides evidence that the relationship is more complex than "cannabis causes psychosis," with shared vulnerability and self-medication playing important roles.

This JAMA Psychiatry study shifts the narrative from a simple causal model (cannabis causes psychosis) to a more nuanced understanding where genetic vulnerability, pre-existing symptoms, and cannabis use may all interact. This has implications for both clinical screening and policy.

ABCD Study follow-up is still relatively short (4 years, ages ~10-15). Cannabis use in this young sample may not represent adult patterns. Self-reported psychosis symptoms are not the same as clinical psychotic disorders. Cannot fully rule out unmeasured confounders.