Continuing an antipsychotic furthers the prevention
STUDY: Mustonen A et al, British Journal of Psychiatry 2025; doi: 10.1192/bjp.2025.72
STUDY TYPE: Cohort study
FUNDING: Swedish Research Council
Background
One in three patients with cannabis-induced psychosis (CIP) eventually converts to schizophrenia — a worse conversion rate than most other substance-induced psychoses. Cannabis also drives medication non-adherence, making relapse prevention especially difficult. This is the first study to examine which specific antipsychotics work best after CIP.
The Study
1,772 patients with a first clinically diagnosed CIP were identified from Swedish national registers and followed a mean of 8 years. The primary outcome was psychiatric hospitalization for any psychotic episode. A within-individual design compared periods of antipsychotic use against periods of non-use, controlling for genetic and baseline confounders.
Any antipsychotic use reduced psychosis hospitalization risk by 25% (aHR 0.75). The standouts were aripiprazole LAI (aHR 0.27) and olanzapine LAI (aHR 0.28) — roughly 72% risk reduction each. Clozapine came next (aHR 0.55), followed by oral aripiprazole (aHR 0.64) and oral olanzapine (aHR 0.81). Quetiapine, oral risperidone, and first-generation LAIs didn’t reach statistical significance. LAIs also reduced substance use disorder hospitalizations.
Practice Implications
- This study suggests cannabis-induced psychosis is not a temporary problem, with high risks of relapse into new psychotic episodes — whether caused by cannabis or not.
- Antipsychotics treat the problem acutely, and may offer long-term prevention, but we’ll need a randomized trial to be sure of that.
- The superiority of long acting injections (LAIs) probably reflects adherence.
— Chris Aiken, MD
Director, Psych Partners
Editor in Chief, Carlat Psychiatry Report
What’s Your Take? Share in Comments
- Are you seeing relapses after psychosis form cannabis?
- Which medications do you find effective?
