Medical cannabis patients had a 38% higher risk of psychosis-related ER visits compared to matched controls in Ontario

Medical cannabis patients had a psychotic disorder incidence of 3.00 per 1,000 person-years compared to 1.88 in controls. The adjusted hazard ratio was 1.38 (95% CI 1.19-1.60) overall and 1.63 (95% CI 1.40-1.91) among patients without previous psychotic disorders, suggesting the risk is particularly elevated in those with no prior psychosis.

Retrospective propensity score-matched cohort study linking clinical data from Ontario cannabis clinics (2014-2019) with health administrative databases. Each cannabis patient matched to up to 3 population-based controls. Conditional Cox regression for hazard ratios.

Most research on cannabis and psychosis focuses on recreational use. This is one of the first large studies to examine psychosis risk specifically in medical cannabis patients, who may differ from recreational users in their conditions, doses, and monitoring.

The higher risk ratio in patients without prior psychosis suggests medical cannabis may pose a particular concern for first-onset psychosis. This complicates the assumption that medical cannabis programs, with clinical oversight, adequately mitigate psychosis risk.

Cannot determine actual cannabis consumption from authorization data. Propensity matching may not capture all confounders. Medical cannabis patients may have conditions that independently increase psychosis risk. Administrative data may not capture all psychotic events.