Cannabis Sales Were Linked to More Drug- and Alcohol-Related Crashes in Quebec
Higher cannabis sales in Quebec were associated with a 12% increase in both drug-related and alcohol-related traffic crashes across five cities, with Montreal showing the strongest effects.
Quick Facts
What This Study Found
Total cannabis sales were significantly associated with a 12% increase in drug-related crashes (IRR 1.12) and a 12% increase in alcohol-related crashes (IRR 1.12) across five Quebec cities. Montreal showed the strongest effects: 87% increase in drug-related crashes and 93% increase in alcohol-related crashes. Longueuil and Quebec City also showed significant increases, while Laval and Sherbrooke showed no significant effects.
Key Numbers
Five cities; 2015-2022; overall IRR 1.12 for both drug and alcohol crashes; Montreal drug-related IRR 1.87, alcohol-related IRR 1.93; Longueuil drug IRR 1.76, alcohol IRR 1.43; Quebec City alcohol IRR 1.44; no significant effects in Laval or Sherbrooke.
How They Did This
Interrupted time-series analysis of daily drug- and alcohol-related traffic crashes in five Quebec cities (Montreal, Quebec City, Laval, Longueuil, Sherbrooke) from 2015-2022. Cannabis sales (legal and estimated illegal) served as exposure variables. Generalized linear models with negative binomial regression and random-effects meta-analysis across cities, controlling for temperature, time trends, and COVID-19 measures.
Why This Research Matters
The finding that cannabis sales are associated with both drug-related AND alcohol-related crashes suggests that cannabis availability may influence broader impaired driving patterns, not just cannabis-impaired driving. This has implications for how jurisdictions plan road safety interventions around legalization.
The Bigger Picture
This study adds to the mixed international evidence on cannabis legalization and road safety. The city-level variation within a single province suggests that local factors (population density, enforcement, transit alternatives) strongly influence outcomes, and that provincial-level analyses may mask important geographic differences.
What This Study Doesn't Tell Us
Ecological design using cannabis sales as a proxy for individual consumption. Cannot establish that individuals in crashes actually used cannabis. The COVID-19 pandemic occurred during the study period and may confound results. Illicit market estimates introduce uncertainty. City-level variation makes it difficult to draw general conclusions.
Questions This Raises
- ?Why are alcohol-related crashes associated with cannabis sales?
- ?Is this due to co-use of substances, or a general relaxation of attitudes toward impaired driving?
- ?Why were some cities affected and others not?
- ?Would stricter roadside testing change these patterns?
Trust & Context
- Key Stat:
- Cannabis sales linked to 87% more drug-related and 93% more alcohol-related crashes in Montreal
- Evidence Grade:
- Moderate: Rigorous time-series design with multiple cities and meta-analysis, but ecological exposure (sales data) and city-level variation limit individual-level conclusions.
- Study Age:
- Published in 2025 with data from 2015-2022.
- Original Title:
- Impact of Canada's Cannabis Act on drug- and alcohol-related collisions in Québec: an interrupted time-series analysis of five major cities.
- Published In:
- Traffic injury prevention, 26(sup1), S77-S85 (2025)
- Authors:
- Nazif-Munoz, José Ignacio(3), Ouimet, Marie Claude(2)
- Database ID:
- RTHC-07245
Evidence Hierarchy
Looks back at existing records to find patterns.
What do these levels mean? →Frequently Asked Questions
Why were alcohol-related crashes linked to cannabis sales?
The study suggests two possibilities: cannabis and alcohol may be used together (co-use leading to impaired driving), or increased cannabis availability may generally affect impaired driving patterns and attitudes. The precise mechanism cannot be determined from the ecological data.
Why did some cities show effects and others did not?
The researchers did not identify specific reasons for the city-level differences. Possible explanations include differences in population density, public transit availability, local enforcement practices, and the relative size of local cannabis markets.
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Cite This Study
https://rethinkthc.com/research/RTHC-07245APA
Nazif-Munoz, José Ignacio; Ouimet, Marie Claude. (2025). Impact of Canada's Cannabis Act on drug- and alcohol-related collisions in Québec: an interrupted time-series analysis of five major cities.. Traffic injury prevention, 26(sup1), S77-S85. https://doi.org/10.1080/15389588.2025.2537145
MLA
Nazif-Munoz, José Ignacio, et al. "Impact of Canada's Cannabis Act on drug- and alcohol-related collisions in Québec: an interrupted time-series analysis of five major cities.." Traffic injury prevention, 2025. https://doi.org/10.1080/15389588.2025.2537145
RethinkTHC
RethinkTHC Research Database. "Impact of Canada's Cannabis Act on drug- and alcohol-related..." RTHC-07245. Retrieved from https://rethinkthc.com/research/nazif-munoz-2025-impact-of-canadas-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.