The study examined the impact of Canada’s legalization of recreational cannabis on the prevalence of adverse events among cannabis users. Data from the International Cannabis Policy Study’s first four waves (2018-2021) were analyzed, including responses from 18,285 Canadians aged 16-65 who reported cannabis use in the past 12 months. The primary outcomes measured were the types of adverse events experienced, medical help-seeking behaviors, and the types of cannabis products used.

Approximately one-third of cannabis consumers reported experiencing at least one adverse event, with 5% seeking medical help, commonly for panic attacks, fainting, heart/blood pressure issues, and nausea/vomiting. The prevalence of seeking help and the types of adverse events remained similar pre (2018) and post-legalization (2019-2021), but there was an increase in emergency room visits post-legalization. Dried flower and oral oils were most associated with adverse events, while help-seeking associated with cannabis edibles significantly decreased after legalization.

The study suggests widespread difficulty in dosing cannabis among consumers, indicating a need for better consumer education. The legalization did not significantly change the prevalence of adverse events reported, but the location of medical help-seeking and products associated changed post-legalization. The findings imply that while the likelihood of an individual experiencing adverse events remained stable, the overall number of adverse events might have increased due to the rise in cannabis use. The decrease in adverse events associated with edibles post-legalization could be attributed to federal product standards limiting THC amounts in these products.

Strengths of the study include a large sample size and national scope, providing estimates of the prevalence of adverse outcomes and the types of products and medical help sought. However, limitations such as reliance on self-reported data, which may be subject to recall and social desirability biases, and the inability to assess individual-level changes over time due to the cross-sectional study design, must be considered. The findings call for more research on the risk of adverse events associated with different cannabis products, especially as product diversity and potency increase. Moreover, the study underscores the importance of continued surveillance of cannabis-related adverse events and a better understanding of racial/ethnic disparities in these events.

Marquette, A., Iraniparast, M., & Hammond, D. (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) doi :