Initial cannabis legalization with product and retail restrictions in Ontario did not increase ER visits for cannabis-induced psychosis, but the subsequent commercialization phase with expanded stores and products was associated with a 30% increase.
Cannabis policy designers, mental health researchers, regulators deciding on retail and product frameworks.
30% increase in cannabis psychosis ER visits after commercialization, none after initial legalization
What the researchers found
Across 6,300 ER visits for cannabis-induced psychosis, restricted legalization showed no change relative to pre-legalization. Commercialization was associated with an immediate 30% increase (IRR 1.30). The increase was driven by youth above the legal purchase age (19-24, IRR 1.63) but not below it (15-18, IRR 0.73, nonsignificant). No changes were seen in cocaine or methamphetamine psychosis ER visits, serving as negative controls.
Why it matters
This study provides a nuanced message: it is not legalization per se that may increase psychosis risk, but rather the commercial expansion phase with more retail stores, more product types, and likely more potent products. The finding that youth above but not below legal purchase age drove the increase suggests retail access matters.
The numbers in context
6,300 ER visits for cannabis-induced psychosis. Commercialization: IRR 1.30 (95% CI 1.02-1.66). Youth 19-24: IRR 1.63 (95% CI 1.27-2.08). Youth 15-18: IRR 0.73 (not significant). No changes in cocaine or methamphetamine psychosis visits.
How the study worked
Population-based study using health administrative data for all ER visits in Ontario, Canada (population 14.3 million) across three periods: pre-legalization (Jan 2014-Sep 2018), legalization with restrictions (Oct 2018-Feb 2020), and commercialization (Mar 2020-Sep 2021). Segmented regression with cocaine and methamphetamine psychosis as controls.
What this study cannot tell us
The commercialization period overlapped with COVID-19, which may have independently affected substance use and mental health. Cannot determine whether potency changes, increased access, or other factors drove the increase. Relies on ER diagnostic coding.
How to read the evidence
Population-level data from a universal healthcare system with appropriate control conditions (cocaine/methamphetamine psychosis) strengthening causal inference.
When this study was published
Published 2023, using 2014-2021 data from Ontario, Canada.
The bigger picture
This is a key finding for jurisdictions designing legalization frameworks. Restricting retail outlets and product types during early legalization may serve as a protective buffer. The jump during commercialization aligns with research on how increased product availability and potency can drive harm.
Questions still open
- Would tighter product potency regulations during commercialization have prevented the increase?
- Is the effect on 19-24 year olds driven by first-time legal access or by increased product availability?
Common questions
Did legalizing cannabis increase psychosis ER visits?
Which age group was most affected?
Read the original research
Association between non-medical cannabis legalization and emergency department visits for cannabis-induced psychosis.
Molecular psychiatry, 28(10), 4251-4260
Citation
Myran, Daniel T; Pugliese, Michael; Roberts, Rhiannon L; Solmi, Marco; Perlman, Christopher M; Fiedorowicz, Jess; Tanuseputro, Peter; Anderson, Kelly K. (2023). Association between non-medical cannabis legalization and emergency department visits for cannabis-induced psychosis.. Molecular psychiatry, 28(10), 4251-4260. https://doi.org/10.1038/s41380-023-02185-x
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