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.
Policymakers, psychiatrists, public health researchers, and anyone following cannabis legalization outcomes.
No significant step change in psychosis visits after legalization (p=0.88)
What the researchers 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.
Why it 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 numbers in context
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 the study worked
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.
What this study cannot 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.
How to read the evidence
Large population-level dataset with appropriate time-series methodology, though limited post-legalization timeframe.
When this study was published
Published in 2022 with data through December 2019, 14 months post-legalization.
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.
Questions still open
- 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?
Common questions
Did cannabis legalization increase psychosis in Canada?
Why might the results not show the full picture?
Read the original research
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
Citation
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
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