Among nearly 3,000 suspected drug-impaired drivers evaluated in Quebec from 2014-2018, cannabis was detected in 48% of cases, while methamphetamine was the most common substance at 54%.
Traffic safety researchers, law enforcement, policymakers, and public health officials.
48% of suspected impaired drivers tested positive for cannabis
What the researchers found
At least one impairing substance was detected in 98% of the 2,982 Drug Recognition Expert cases. Cannabis (THC-COOH) was found in 48% of cases. Polydrug use was common, with 79% of cases showing two or more impairing substances.
Why it matters
Establishing a pre-legalization baseline of drug-impaired driving patterns helps researchers and policymakers measure the impact of recreational cannabis legalization on road safety.
The numbers in context
Total cases: 2,982. Substance detected: 98%. Cannabis positive: 48%. Methamphetamine: 54%. Cocaine: 29%. GHB: 24%. Polydrug use: 79%. Average age: 33. Male: 79%.
How the study worked
Retrospective analysis of 2,982 Drug Recognition Expert evaluation cases in Quebec, Canada from January 2014 to December 2018. All biological samples underwent targeted LC-MS/MS analysis for 137 drugs and metabolites.
What this study cannot tell us
Only captures drivers flagged by police, not all impaired drivers. THC-COOH indicates past use rather than active impairment. Results reflect Quebec-specific drug culture and may not generalize.
How to read the evidence
Comprehensive toxicological analysis with validated methods, though limited to drivers already flagged for impairment.
When this study was published
Published in 2021 covering 2014-2018, the period just before Canadian cannabis legalization.
The bigger picture
This pre-legalization snapshot provides a critical baseline for understanding how cannabis policy changes affect driving behavior and drug detection patterns.
Questions still open
- How have these detection patterns changed since cannabis legalization in October 2018? Does polydrug use complicate impairment assessment for DREs?
Common questions
What was the most common drug found in suspected impaired drivers?
How common was polydrug use among suspected impaired drivers?
Read the original research
Drugs and driving prior to cannabis legalization: A 5-year review from DECP (DRE) cases in the province of Quebec, Canada.
Accident; analysis and prevention, 149, 105832
Citation
Vaillancourt, Lucie; Viel, Edith; Dombrowski, Cynthia; Desharnais, Brigitte; Mireault, Pascal. (2021). Drugs and driving prior to cannabis legalization: A 5-year review from DECP (DRE) cases in the province of Quebec, Canada.. Accident; analysis and prevention, 149, 105832. https://doi.org/10.1016/j.aap.2020.105832