After Canadian Legalization, Only People With Schizophrenia Increased Cannabis Use

The odds of daily/near-daily cannabis use increased nine-fold (aOR=9.19) among people with schizophrenia between pre-legalization (2018) and two years post (2020). Their average monthly use days rose from 12.8 to 18.1. No significant changes were observed for cannabis users with anxiety, depression, PTSD, bipolar disorder, substance use disorders, or no mental health conditions.

Repeated cross-sectional analysis of 13,527 Canadian respondents across three waves of the International Cannabis Policy Study (Wave 1: Aug-Oct 2018; Wave 2: Sep-Oct 2019; Wave 3: Sep-Nov 2020). Analysis focused on cannabis users with specific self-reported mental health disorders.

Cannabis legalization advocates often cite that the sky will not fall, while opponents worry about vulnerable populations. This study suggests both are partially right: legalization did not increase use for most people with mental health conditions, but people with schizophrenia, who are particularly vulnerable to cannabis harms, were the exception.

The specificity of the finding to schizophrenia is striking. People with psychotic disorders may be particularly drawn to cannabis for symptom self-management, but increased use in this group carries real risks given the established link between cannabis and psychotic episodes.

Self-reported mental health diagnoses may be inaccurate. The schizophrenia subsample was likely small, contributing to the very wide confidence interval (2.46-34.37). Cross-sectional design means different people were surveyed at each wave. Cannot determine causation.