Cannabis co-involvement in self-harm ER visits increased 90% from 2010 to 2021, with the entire increase after medical cannabis liberalization, while alcohol-involved self-harm declined 17%.
Emergency psychiatrists, crisis specialists, cannabis policy researchers, and public health professionals.
What the researchers found
Among 158,912 self-harm ER visits, cannabis co-diagnosis increased 90.1% (3.6 to 6.9/100,000) while alcohol declined 17.3%. The entire cannabis increase occurred after medical liberalization (asRR 1.71) with no additional increase during recreational legalization.
Why it matters
The parallel trends and timing alignment with medical liberalization suggest a real shift in which substances co-occur with self-harm, though whether cannabis is contributing or just more commonly detected remains unclear.
The numbers in context
158,912 self-harm visits. 7,810 (4.9%) with cannabis. 24,761 (15.6%) with alcohol. Cannabis: +90.1%. Alcohol: -17.3%. Increase began after medical liberalization (asRR 1.71).
How the study worked
Repeated cross-sectional study using Ontario administrative data (2010-2021). Poisson regression across four cannabis policy periods.
What this study cannot tell us
Cannot determine causation. Cannabis may cause more self-harm, people at risk may use more cannabis, or clinicians may test more. COVID confounds final period.
How to read the evidence
Large population study with clear temporal analysis. Cannot establish whether cannabis is causing more self-harm or is increasingly co-present.
When this study was published
2024 publication using 2010-2021 data.
The bigger picture
Rising cannabis involvement in self-harm coinciding with declining alcohol involvement suggests the substance landscape around mental health crises is shifting.
Questions still open
- Is the increase driven by more use, more testing, or genuine causation?
- Should cannabis screening become standard in self-harm presentations?
Common questions
Does cannabis increase self-harm risk?
Why did the increase start with medical liberalization?
Read the original research
Cannabis-involvement in emergency department visits for self-harm following medical and non-medical cannabis legalization.
Journal of affective disorders, 351, 853-862
Citation
Myran, Daniel T; Gaudreault, Adrienne; Pugliese, Michael; Tanuseputro, Peter; Saunders, Natasha. (2024). Cannabis-involvement in emergency department visits for self-harm following medical and non-medical cannabis legalization.. Journal of affective disorders, 351, 853-862. https://doi.org/10.1016/j.jad.2024.01.264
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