Among over 13,000 Canadian cannabis users surveyed before and after legalization, only those with schizophrenia showed significant increases in daily use and monthly frequency, while users with other mental health conditions showed no change.
Psychiatrists, cannabis policy researchers, and mental health advocates
9-fold increase in daily use odds among people with schizophrenia post-legalization
What the researchers found
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.
Why it matters
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 numbers in context
N=13,527. Schizophrenia daily use OR: 9.19 (95% CI: 2.46-34.37) from Wave 1 to Wave 3. Monthly use days increased from 12.8 to 18.1 for schizophrenia group. No significant changes for anxiety, depression, PTSD, bipolar, SUD, or no-mental-health groups.
How the study worked
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.
What this study cannot tell us
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.
How to read the evidence
Large multi-wave survey with appropriate statistical adjustments, but cross-sectional design and small schizophrenia subsample limit confidence.
When this study was published
2024 study using 2018-2020 data
The bigger picture
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.
Questions still open
- Why did only people with schizophrenia increase their use? Are they self-medicating specific symptoms? Would targeted public health messaging reach this population? Has the trend continued beyond 2020?
Common questions
Did cannabis legalization in Canada increase use among people with mental health conditions?
Why is increased cannabis use concerning for people with schizophrenia?
Read the original research
Changes in Cannabis Use Patterns in Psychiatric Populations Pre- and Post-Legalization of Recreational Cannabis Use in Canada: A Repeated Cross-Sectional Survey.
Cannabis (Albuquerque, N.M.), 7(3), 1-13
Citation
Sorkhou, Maryam; Johnstone, Samantha; Weinberger, Andrea H; Cooper, Ziva D; Sanches, Marcos; Castle, David J; Hall, Wayne; Rabin, Rachel A; Hammond, David; George, Tony P. (2024). Changes in Cannabis Use Patterns in Psychiatric Populations Pre- and Post-Legalization of Recreational Cannabis Use in Canada: A Repeated Cross-Sectional Survey.. Cannabis (Albuquerque, N.M.), 7(3), 1-13. https://doi.org/10.26828/cannabis/2024/000238
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