Analysis of over 239,000 traffic-injury emergency visits in Ontario and Alberta found no significant increase in driver injuries after cannabis was legalized in Canada in October 2018.
Policymakers evaluating cannabis legalization impacts, road safety researchers, public health professionals
No significant change in traffic injuries after legalization in either province
What the researchers found
There was no evidence of significant changes in traffic-injury ED visits after cannabis legalization in either province, for all drivers or youth drivers specifically. Results were non-significant in all four analyses (Alberta all drivers p=0.52, Alberta youth p=0.42, Ontario all drivers p=0.30, Ontario youth p=0.98).
Why it matters
A primary concern about cannabis legalization was increased traffic injuries. This large population-level study from two major Canadian provinces provides reassuring evidence that this feared outcome did not materialize in the first year.
The numbers in context
Alberta: 52,752 all-driver presentations, 3,265 youth; Ontario: 186,921 all-driver, 4,565 youth; no significant changes post-legalization across all four analyses
How the study worked
SARIMA time series analysis of weekly provincial emergency department records from April 2015 to December 2019 in Alberta and Ontario, examining driver traffic-injury presentations before and after legalization (October 17, 2018).
What this study cannot tell us
Only 14 months of post-legalization data. ED visits may not capture all traffic injuries. Does not measure cannabis-impaired driving directly. Early legalization period may not reflect long-term trends.
How to read the evidence
Large population-level time series analysis across two provinces with robust statistical methods
When this study was published
Published in 2021 covering through December 2019. Only 14 months of post-legalization data were available.
The bigger picture
This adds to evidence from U.S. states suggesting that cannabis legalization does not necessarily increase traffic injuries at the population level, though individual impaired driving remains a concern.
Questions still open
- Would longer follow-up reveal delayed effects? Did cannabis-impaired driving increase but was offset by other safety improvements? Are there specific demographics or regions where traffic injuries did increase?
Common questions
Did cannabis legalization increase traffic injuries in Canada?
Were youth drivers affected by legalization?
Read the original research
Canada's cannabis legalization and drivers' traffic-injury presentations to emergency departments in Ontario and Alberta, 2015-2019.
Drug and alcohol dependence, 228, 109008
Citation
Callaghan, Russell C; Sanches, Marcos; Vander Heiden, Julia; Asbridge, Mark; Stockwell, Tim; Macdonald, Scott; Peterman, Bronwen Hughes; Kish, Stephen J. (2021). Canada's cannabis legalization and drivers' traffic-injury presentations to emergency departments in Ontario and Alberta, 2015-2019.. Drug and alcohol dependence, 228, 109008. https://doi.org/10.1016/j.drugalcdep.2021.109008