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Association between non-medical cannabis legalization and emergency department visits for cannabis-induced psychosis

Molecular Psychiatry volume 28, pages 4251–4260 (2023)Cite this article

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Abstract

A major public health concern of cannabis legalization is that it may result in an increase in psychotic disorders. We examined changes in emergency department (ED) visits for cannabis-induced psychosis following the legalization and subsequent commercialization (removal of restrictions on retail stores and product types) of non-medical cannabis in Ontario, Canada (population of 14.3 million). We used health administrative data containing the cause of all ED visits to examine changes over three periods; 1) pre-legalization (January 2014–September 2018); 2) legalization with restrictions (October 2018 – February 2020); and 3) commercialization (March 2020 – September 2021). We considered subgroups stratified by age and sex and examined cocaine- and methamphetamine-induced psychosis ED visits as controls. During our study, there were 6300 ED visits for cannabis-induced psychosis. The restricted legalization period was not associated with changes in rates of ED visits for cannabis-induced psychosis relative to pre-legalization. The commercialization period was associated with an immediate increase in rates of ED visits for cannabis-induced psychosis (IRR 1.30, 95% CI 1.02–1.66) and no gradual monthly change; immediate increases were seen only for youth above (IRR 1.63, 1.27–2.08, ages 19–24) but not below (IRR 0.73 95%CI 0.42–1.28 ages, 15–18) the legal age of purchase, and similar for men and women. Commercialization was not associated with changes in rates of ED visits for cocaine- or methamphetamine-induced psychosis. This suggests that legalization with store and product restrictions does not increase ED visits for cannabis-induced psychosis. In contrast, cannabis commercialization may increase cannabis-induced psychosis presentations highlighting the importance of preventive measures in regions considering legalization.

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Fig. 1: Observed and predicted rates of ED visits during different phases of non-medical cannabis legalization in Ontario.
Fig. 2: Observed and predicted rates of ED visits per 100,000 individuals during different phases of non-medical cannabis legalization in Ontario for cannabis- cocaine- and methamphetamine-induced psychosis.

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Data availability

The dataset from this study is held securely in coded form at ICES. While legal data sharing agreements between ICES and data providers (e.g., healthcare organizations and government) prohibit ICES from making the dataset publicly available, access may be granted to those who meet pre-specified criteria for confidential access, available at www.ices.on.ca/DAS (email: das@ices.on.ca). The full dataset creation plan and underlying analytic code are available from the authors upon request, understanding that the computer programs may rely upon coding templates or macros that are unique to ICES and are therefore either inaccessible or may require modification.

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Funding

D.T.M. was supported with a Research Fellow Salary Award from the Canadian Institutes of Health Research and the University of Ottawa Department of Family Medicine. P.T. was supported by a PSI Graham Farquharson Knowledge Translation Fellowship. This study was supported by the University of Ottawa site of ICES, which is funded by an annual grant from the Ontario Ministry of Health and Ministry of Long-Term Care. This study also received funding from Canadian Institutes for Health Research Project Grant (452360).

Author information

Author notes

  1. These authors jointly supervised this work: Peter Tanuseputro, Kelly K. Anderson.

Authors and Affiliations

  1. Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, ON, Canada

    Daniel T. Myran, Rhiannon L. Roberts, Marco Solmi, Jess Fiedorowicz & Peter Tanuseputro

  2. Department of Family Medicine, University of Ottawa, Ottawa, ON, Canada

    Daniel T. Myran

  3. ICES uOttawa, Ottawa Hospital Research Institute, Ottawa, ON, Canada

    Daniel T. Myran & Michael Pugliese

  4. Bruyère Research Institute, Ottawa, ON, Canada

    Daniel T. Myran & Peter Tanuseputro

  5. Department of Psychiatry, University of Ottawa, Ottawa, ON, Canada

    Marco Solmi & Jess Fiedorowicz

  6. Department of Mental Health, The Ottawa Hospital, Ottawa, ON, Canada

    Marco Solmi & Jess Fiedorowicz

  7. School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, ON, Canada

    Marco Solmi, Jess Fiedorowicz & Peter Tanuseputro

  8. Department of Child and Adolescent Psychiatry, Charité Universitätsmedizin, Berlin, Germany

    Marco Solmi

  9. School of Public Health Sciences, University of Waterloo, Waterloo, ON, Canada

    Christopher M. Perlman

  10. Neurosciences, Ottawa Hospital Research Institute, Ottawa, ON, Canada

    Jess Fiedorowicz

  11. Department of Medicine, University of Ottawa, Ottawa, ON, Canada

    Peter Tanuseputro

  12. Departments of Epidemiology & Biostatistics and Psychiatry, Western University, London, ON, Canada

    Kelly K. Anderson

  13. ICES Western, London, ON, Canada

    Kelly K. Anderson

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Contributions

D.T.M. and M.P. had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Concept and design: D.T.M., R.L.R, P.T., K.K.A. Acquisition, analysis, or interpretation of data: All authors. Drafting of the manuscript: D.T.M. Critical revision of the manuscript for important intellectual content: All authors. Statistical analysis: D.T.M., M.P. Obtained funding: D.T.M., P.T. Administrative, technical, or material support: D.T.M., R.L.R. Supervision: D.T.M., P.T., K.K.A.

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Correspondence to Daniel T. Myran.

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Competing interests

Marco Solmi has received honoraria/has been a consultant for Angelini, Lundbeck, Otsuka. Other authors declare no competing interests.

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Myran, D.T., Pugliese, M., Roberts, R.L. et al. Association between non-medical cannabis legalization and emergency department visits for cannabis-induced psychosis. Mol Psychiatry 28, 4251–4260 (2023). https://doi.org/10.1038/s41380-023-02185-x

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