Cannabis Use Among Forensic Mental Health Patients Rose After Canadian Legalization, With Clinical Consequences | Research

The takeaway

Among 187 forensic psychiatric patients in Ontario, cannabis use increased significantly after legalization, with over half experiencing mental health deterioration in the week following use, though actual violence rates did not increase.

Forensic psychiatrists, mental health policy makers, and legalization impact researchers.

Over half of forensic patients who used cannabis experienced mental health worsening within a week

What the researchers found

One-third of forensic patients used cannabis over the study period, with frequency increasing significantly after legalization. Those who used cannabis were more likely to be readmitted to hospital and had higher static risk factors for violence. Over half experienced mental health worsening within a week of use. However, actual violence rates did not differ between users and non-users.

Why it matters

Forensic mental health patients represent one of the populations most vulnerable to cannabis-related harms. This study provides direct evidence that legalization increased cannabis use in this population and that use was associated with clinical deterioration, even if not with violence.

The numbers in context

187 patients; one-third used cannabis; use frequency increased post-legalization; 50%+ experienced mental health worsening within a week of use; higher hospital readmission in users; no difference in violence rates

How the study worked

Pseudo-prospective study of 187 forensic mental health patients in Ontario over four years (two pre- and two post-legalization), tracking cannabis use frequency, clinical outcomes, and safety measures.

What this study cannot tell us

Single province (Ontario). Relatively small sample. Cannabis use detected through self-report and urine testing, which may miss some use. Could not control for cannabis potency or product type. Pre-post design limits causal inference.

How to read the evidence

Pseudo-prospective design with direct clinical outcome measurement, but small sample and single-province design limit conclusions.

When this study was published

Published in 2024.

The bigger picture

This study is among the first to directly examine legalization's impact on forensic psychiatric patients. The dissociation between clinical deterioration and violence is important: cannabis harmed these patients' mental health and recovery without making them more dangerous to others.

Questions still open

Should forensic mental health systems implement cannabis-specific interventions post-legalization?
Would legalization with better clinical safeguards for psychiatric populations change these outcomes?

Common questions

Did cannabis legalization make forensic patients more dangerous?

No. While cannabis use increased and was linked to clinical deterioration, actual violence rates did not differ between patients who used cannabis and those who did not.

How did legalization affect cannabis use in this population?

Cannabis use frequency among forensic patients increased gradually and significantly after legalization, with one-third of patients using cannabis during the study period.

Read the original research

Clinical and public safety risks associated with cannabis legalization and frequency of cannabis use among forensic mental health patients.

The International journal on drug policy, 134, 104622

View on PubMed ↗Publisher’s paper ↗

Citation

Penney, Stephanie R; Jones, Roland M; Wilkie, Treena; Gerritsen, Cory; Chatterjee, Sumeeta; Chaimowitz, Gary A; Simpson, Alexander I F. (2024). Clinical and public safety risks associated with cannabis legalization and frequency of cannabis use among forensic mental health patients.. The International journal on drug policy, 134, 104622. https://doi.org/10.1016/j.drugpo.2024.104622