Canada's cannabis legalization was not associated with increased psychosis-related ER visits in Ontario and Alberta
Despite cannabis-induced psychosis ER visits doubling from 2015 to 2019, statistical analysis found no significant jump in visits attributable to Canada's 2018 legalization for either cannabis-induced psychosis or schizophrenia.
Quick Facts
What This Study Found
Cannabis-induced psychosis ED presentations doubled between April 2015 and December 2019. However, SARIMA models found no significant step-function effects of legalization on weekly ED counts for cannabis-induced psychosis (0.34, 95% CI -4.1 to 4.8, p=0.88), schizophrenia (24.34, 95% CI -18.3 to 67.0, p=0.26), alcohol-induced psychosis, or amphetamine-induced psychosis.
Key Numbers
5,832 cannabis-induced psychosis visits; 211,661 schizophrenia visits; 10,829 amphetamine-induced psychosis visits; 1,884 alcohol-induced psychosis visits analyzed. None showed significant step changes after October 2018 legalization.
How They Did This
Population-level analysis of ED presentations across Alberta and Ontario from April 2015 to December 2019. Seasonal Autoregressive Integrated Moving Average (SARIMA) models assessed whether the October 2018 Cannabis Act was associated with step changes in weekly ED counts for four ICD-10-defined conditions.
Why This Research Matters
One of the strongest fears about cannabis legalization is increased psychosis burden. This large-scale Canadian analysis found no evidence that legalization itself caused a sudden increase, though the ongoing upward trend warrants monitoring.
The Bigger Picture
The doubling of cannabis-induced psychosis visits occurred as a gradual trend, not a sudden jump at legalization. This suggests broader factors (increasing use, higher potency, greater diagnostic awareness) rather than legalization per se are driving the increase.
What This Study Doesn't Tell Us
Only 14 months of post-legalization data. Gradual rollout of retail stores may delay full effects. Administrative data may not capture all psychosis cases. SARIMA models test for step changes, not gradual shifts. Two provinces may not represent all of Canada.
Questions This Raises
- ?Would a longer post-legalization period reveal delayed effects?
- ?Does the gradual increase in cannabis-induced psychosis reflect true increased incidence or improved diagnosis?
- ?Will the introduction of edibles and concentrates change these trends?
Trust & Context
- Key Stat:
- No significant step change in psychosis visits after legalization (p=0.88)
- Evidence Grade:
- Large population-level dataset with appropriate time-series methodology, though limited post-legalization timeframe.
- Study Age:
- Published in 2022 with data through December 2019, 14 months post-legalization.
- Original Title:
- Associations Between Canada's Cannabis Legalization and Emergency Department Presentations for Transient Cannabis-Induced Psychosis and Schizophrenia Conditions: Ontario and Alberta, 2015-2019.
- Published In:
- Canadian journal of psychiatry. Revue canadienne de psychiatrie, 67(8), 616-625 (2022)
- Authors:
- Callaghan, Russell C(2), Sanches, Marcos(8), Murray, Robin M(27), Konefal, Sarah, Maloney-Hall, Bridget, Kish, Stephen J
- Database ID:
- RTHC-03739
Evidence Hierarchy
Looks back at existing records to find patterns.
What do these levels mean? →Frequently Asked Questions
Did cannabis legalization increase psychosis in Canada?
Cannabis-induced psychosis ER visits doubled from 2015 to 2019, but this increase was a gradual pre-existing trend, not a sudden jump at legalization. Statistical models found no significant change attributable to the October 2018 Cannabis Act.
Why might the results not show the full picture?
Only 14 months of post-legalization data were available, and cannabis retail stores opened gradually. Longer follow-up with full market maturation may reveal effects not yet detectable.
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Cite This Study
https://rethinkthc.com/research/RTHC-03739APA
Callaghan, Russell C; Sanches, Marcos; Murray, Robin M; Konefal, Sarah; Maloney-Hall, Bridget; Kish, Stephen J. (2022). Associations Between Canada's Cannabis Legalization and Emergency Department Presentations for Transient Cannabis-Induced Psychosis and Schizophrenia Conditions: Ontario and Alberta, 2015-2019.. Canadian journal of psychiatry. Revue canadienne de psychiatrie, 67(8), 616-625. https://doi.org/10.1177/07067437211070650
MLA
Callaghan, Russell C, et al. "Associations Between Canada's Cannabis Legalization and Emergency Department Presentations for Transient Cannabis-Induced Psychosis and Schizophrenia Conditions: Ontario and Alberta, 2015-2019.." Canadian journal of psychiatry. Revue canadienne de psychiatrie, 2022. https://doi.org/10.1177/07067437211070650
RethinkTHC
RethinkTHC Research Database. "Associations Between Canada's Cannabis Legalization and Emer..." RTHC-03739. Retrieved from https://rethinkthc.com/research/callaghan-2022-associations-between-canadas-cannabis
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.