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

The takeaway

Among 54,006 Ontario medical cannabis patients matched to 161,265 controls, medical cannabis authorization was associated with a 38% higher risk of ER visits or hospitalizations for psychotic disorders, rising to 63% for those with no prior psychosis history.

Physicians authorizing medical cannabis; medical cannabis program administrators designing safety protocols.

63% higher psychosis risk in patients with no prior history

What the researchers found

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.

Why it matters

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 numbers in context

54,006 cannabis patients matched to 161,265 controls. 39% aged 50 or under. 54% female. Psychotic disorder incidence: 3.00 vs 1.88 per 1,000 person-years. aHR 1.38 (total sample). aHR 1.63 (no prior psychosis).

How the study worked

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.

What this study cannot tell us

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.

How to read the evidence

Large propensity-matched cohort with administrative health data, strong methodology for an observational study.

When this study was published

2024 study

The bigger picture

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.

Questions still open

Does the risk vary by THC-to-CBD ratio or dose? Would psychosis screening before authorization reduce these events?

Common questions

Does this mean medical cannabis is more dangerous than recreational?

Not necessarily. Medical cannabis patients may have underlying conditions that increase psychosis risk. The study compared to non-cannabis-users, not recreational users.

Should medical cannabis programs screen for psychosis risk?

The authors suggest cannabis authorization should include benefit-risk assessment for psychotic disorders. Current screening practices vary widely between programs.

Read the original research

Medical cannabis authorization and risk of emergency department visits and hospitalization due to psychotic disorders: A propensity score-matched cohort study.

Schizophrenia research, 264, 534-542

View on PubMed ↗Publisher’s paper ↗

Citation

Dubois, Cerina; Lunghi, Carlotta; Eurich, Dean T; Dyck, Jason R B; Hyshka, Elaine; Hanlon, John G; Zongo, Arsene. (2024). Medical cannabis authorization and risk of emergency department visits and hospitalization due to psychotic disorders: A propensity score-matched cohort study.. Schizophrenia research, 264, 534-542. https://doi.org/10.1016/j.schres.2024.01.029