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.
Traffic safety researchers, cannabis policy analysts, law enforcement planners in legalized jurisdictions.
Cannabis sales linked to 87% more drug-related and 93% more alcohol-related crashes in Montreal
What the researchers 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.
Why it 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 numbers in context
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 the study worked
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.
What this study cannot 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.
How to read the evidence
Moderate: Rigorous time-series design with multiple cities and meta-analysis, but ecological exposure (sales data) and city-level variation limit individual-level conclusions.
When this study was published
Published in 2025 with data from 2015-2022.
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.
Questions still open
- 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?
Common questions
Why were alcohol-related crashes linked to cannabis sales?
Why did some cities show effects and others did not?
Read the original research
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
Citation
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
Explore the wider topic
- Surviving 4/20 Sober: A Practical Survival Guide
- CBT for Cannabis Recovery: How Cognitive Behavioral Therapy Works
- The Cannabis Relapse Cycle: Quit, Feel Good, Get Complacent, Repeat
- Cold Turkey vs Tapering: Which Way to Quit Weed
- Dating Sober After Years of Being High: What Nobody Tells You
- Exercise as Medicine: Working Out After Quitting Weed
- Grieving Weed Itself: Mourning the Loss of a Companion
- How to Help Someone Quit Weed (When They're Not Ready)
- How to Quit Weed: A No-Judgment Step by Step Guide
- Journaling Through Weed Withdrawal: Why Writing Helps You Heal
- MA vs SMART Recovery vs Therapy: Comparing Your Options
- Meditation and Mindfulness for Weed Withdrawal
- Your Partner Still Smokes Weed: How to Navigate It
- Quitting Weed While Your Partner Still Smokes
- The Pink Cloud Effect: When Quitting Weed Feels Too Good
- How to Quit Smoking Weed Cold Turkey: What to Expect
- Quit Weed or Cut Back: Which Is Right for You?
- I Quit Weed and Regret It: An Honest Look at Non-Linear Recovery
- Quitting Weed in Your 20s: Career, Social Life, Starting Over
- Quitting Weed in Your 30s: It's Not Too Late
- Quitting Weed After 10+ Years of Daily Use: What to Expect
- Quitting Weed During a Life Crisis: Divorce, Job Loss, and Other Bad Timing
- Quitting Weed and Working Out: How Exercise Helps Recovery
- Quitting Weed After Loss: When Grief Comes Flooding Back
- Quitting Weed When It's Legal Everywhere
- Weed Withdrawal Success Stories: Real People Who Made It Through
- Quitting Weed Long Distance: When You Can't Remove Triggers
- I Relapsed on Weed. Now What? A Practical Reset Guide
- I Relapsed After Quitting Weed: What Now?
- Should I Quit Weed? A Decision Framework (Not a Lecture)
- Quitting Weed at Music Festivals and Concerts: A Sober Survival Guide
- Supplements That Actually Help with Weed Withdrawal (And Ones That Don't)
- How to Tell Your Friends You're Quitting Weed
- Relapse Prevention Plan for Cannabis: A CBT-Based Approach
- Why Weed Relapse Happens: The Science Behind Going Back
- Replacing the Ritual: What to Do When You Quit Weed
- How Cannabis Damaged My Relationships: Before and After
- Social Media Detox from Weed Content