How Cannabis Adverse Events Changed After Canada Legalized Recreational Use
About one-third of Canadian cannabis users reported adverse events before and after legalization, with little change in overall rates but a shift toward more ER visits post-legalization.
Quick Facts
What This Study Found
Approximately one-third of cannabis users reported at least one adverse event in the past year, and 5% sought medical help. The prevalence was similar before (2018) and after legalization (2019-2021), but ER visits increased post-legalization while edible-related help-seeking decreased.
Key Numbers
18,285 respondents across 4 waves. ~33% reported at least one adverse event. 5% sought medical help. ER proportion increased (F=2.77, p=0.041). Edible-related help-seeking decreased (p=0.001).
How They Did This
Cross-sectional analysis of four survey waves from the International Cannabis Policy Study (2018-2021) covering 18,285 Canadian respondents aged 16-65 who reported cannabis use.
Why This Research Matters
This is one of the first studies tracking adverse events across the legalization transition in Canada, providing real-world data on whether legalization changes the pattern of harms.
The Bigger Picture
The stable rate of adverse events suggests legalization did not increase harms, but the shift to ER visits may reflect changing product types or greater willingness to seek formal help.
What This Study Doesn't Tell Us
Self-report data subject to recall bias. Online survey may not represent all users. Cannot determine whether changes are caused by legalization or other factors.
Questions This Raises
- ?Does the decrease in edible-related adverse events reflect better dosing information in the legal market?
- ?Will adverse event patterns stabilize as the legal market matures?
Trust & Context
- Key Stat:
- ~33% reported adverse events; ER visits increased post-legalization while edible problems decreased
- Evidence Grade:
- Large sample across the legalization transition, though online self-report and inability to control for confounders limit certainty.
- Study Age:
- Published in 2024 with data from 2018-2021.
- Original Title:
- Adverse outcomes of cannabis use in Canada, before and after legalisation of non-medical cannabis: cross-sectional analysis of the International Cannabis Policy Study.
- Published In:
- BMJ open, 14(1), e077908 (2024)
- Authors:
- Marquette, Anastasia(2), Iraniparast, Maryam(4), Hammond, David(36)
- Database ID:
- RTHC-05516
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
Did legalization make cannabis use more dangerous?
Adverse event rates were similar before and after legalization. ER visits increased but edible-related problems decreased, suggesting shifting patterns rather than increased overall harm.
What are the most common cannabis adverse events?
The most common reasons for seeking medical help were panic attacks, dizziness/fainting, heart/blood pressure problems, and nausea/vomiting.
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Cite This Study
https://rethinkthc.com/research/RTHC-05516APA
Marquette, Anastasia; Iraniparast, Maryam; Hammond, David. (2024). Adverse outcomes of cannabis use in Canada, before and after legalisation of non-medical cannabis: cross-sectional analysis of the International Cannabis Policy Study.. BMJ open, 14(1), e077908. https://doi.org/10.1136/bmjopen-2023-077908
MLA
Marquette, Anastasia, et al. "Adverse outcomes of cannabis use in Canada, before and after legalisation of non-medical cannabis: cross-sectional analysis of the International Cannabis Policy Study.." BMJ open, 2024. https://doi.org/10.1136/bmjopen-2023-077908
RethinkTHC
RethinkTHC Research Database. "Adverse outcomes of cannabis use in Canada, before and after..." RTHC-05516. Retrieved from https://rethinkthc.com/research/marquette-2024-adverse-outcomes-of-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.