Over Half of Injured Canadian Drivers Had Drugs or Alcohol in Their Blood — THC Was the Most Common Drug
Blood tests from 8,328 injured drivers at 15 Canadian trauma centers found 54.9% had at least one substance detected, with THC being the most commonly found drug after alcohol.
Quick Facts
What This Study Found
This is one of the largest and most rigorous studies of substance use among injured drivers ever conducted. Rather than relying on self-report or police records, researchers prospectively collected blood samples from 8,328 injured drivers treated at 15 Canadian trauma centers from 2019 to 2023 — spanning the period after Canada's 2018 recreational cannabis legalization.
The headline: 54.9% of injured drivers had at least one impairing substance in their blood. More than half. The specific breakdown reveals the scale of the problem across substance classes.
Alcohol was the most prevalent, as expected. But THC was the most commonly detected drug (after alcohol), confirming that cannabis-involved driving is a significant component of the impaired driving landscape in post-legalization Canada. Stimulants, opioids, and depressants were also detected, often in combination with other substances.
The study identified demographic and collision factors associated with substance use, and notably compared prevalence across different parts of Canada, revealing geographic variation in the drug-involved driving picture.
Polysubstance use (multiple substances simultaneously) was common, adding to the clinical complexity — the effects of THC combined with alcohol or other drugs on driving may be different from the effects of any single substance.
Key Numbers
8,328 injured drivers. Mean age 43 years. 67.3% male. 54.9% had at least one substance detected. THC was the most common drug after alcohol. 15 trauma centers across Canada. Study period: January 2019 – June 2023 (post-legalization).
How They Did This
Cross-sectional study with prospective blood collection from 8,328 injured drivers at 15 Canadian trauma centers (January 2019 – June 2023). Blood tested for THC, alcohol, stimulants, opioids, and depressants. Demographic and collision details extracted from medical records. Crude prevalence computed overall and by subgroup. Logistic regression identified factors associated with substance use.
Why This Research Matters
Canada legalized recreational cannabis in 2018 with the explicit goal of reducing harms, including impaired driving. This study provides the most comprehensive post-legalization snapshot of substance-involved driving injuries, showing that THC is a major part of the picture. The 54.9% overall prevalence rate is a sobering number for traffic safety policy.
The Bigger Picture
This large-scale Canadian data set complements the driving cluster in the database: RTHC-00092 (Italian DUI blood draw delays), RTHC-00093 and RTHC-00121 (self-assessed driving impairment), RTHC-00124 (Wisconsin DUI delays). While those studies examined the detection and measurement side, this study documents the sheer prevalence — over half of injured drivers testing positive for something, with THC as the top drug. The post-legalization timing makes this particularly relevant for countries and states considering cannabis legalization.
What This Study Doesn't Tell Us
Only includes injured drivers who reached trauma centers — not all impaired driving incidents, and not uninjured impaired drivers. Blood collection may have been delayed (as documented in RTHC-00092 and RTHC-00124), potentially missing some THC-positive cases. Detection of a substance in blood doesn't prove impairment at the time of the crash. No pre-legalization comparison from the same trauma centers, making it impossible to determine whether legalization changed prevalence. Cannot distinguish between driver-at-fault and not-at-fault for drug involvement.
Questions This Raises
- ?Did cannabis legalization increase the prevalence of THC-positive injured drivers compared to the pre-legalization period?
- ?What proportion of THC-positive drivers were actually impaired versus having residual THC from prior use?
- ?Does polysubstance use (THC + alcohol, for example) produce worse crash outcomes than single-substance impairment?
- ?Are there effective public health interventions that reduce cannabis-impaired driving after legalization?
Trust & Context
- Key Stat:
- Evidence Grade:
- Large cross-sectional study with prospective blood collection from multiple trauma centers. The objective blood testing (rather than self-report) is a major strength. Limited by the lack of pre-legalization comparison and inability to prove impairment from detection alone.
- Study Age:
- Published in 2025 with data through June 2023. This represents the most comprehensive post-legalization impaired driving data from Canada.
- Original Title:
- Prevalence of Impairing Substance Use in Injured Drivers.
- Published In:
- JAMA network open, 8(4), e256379 (2025) — JAMA Network Open is a reputable, peer-reviewed medical journal known for publishing high-quality research.
- Authors:
- Brubacher, Jeffrey R(5), Erdelyi, Shannon(3), Chan, Herbert(5), Simmons, Sarah, Atkinson, Paul, Besserer, Floyd, Clarke, David B, Davis, Phil, Daoust, Raoul, Émond, Marcel, Eppler, Jeff, Lee, Jacques S, MacPherson, Andrew, Magee, Kirk, Mercier, Eric, Ohle, Robert, Parsons, Mike, Rao, Jagadish, Rowe, Brian H, Taylor, John, Vaillancourt, Christian, Wishart, Ian
- Database ID:
- RTHC-06126
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Read More on RethinkTHC
- 420-sober-survival-guide
- CBT-cannabis-recovery
- cannabis-relapse-cycle-pattern
- cold-turkey-vs-taper-quit-weed
- dating-sober-after-quitting-weed
- exercise-quitting-weed-anxiety-brain
- grieving-quitting-weed-loss
- help-someone-quit-weed
- how-to-quit-weed
- journaling-weed-withdrawal
- marijuana-anonymous-SMART-recovery-compare
- meditation-mindfulness-weed-withdrawal
- partner-still-smokes-weed
- partner-still-smokes-weed-quitting
- pink-cloud-sobriety-cannabis
- quit-weed-cold-turkey
- quit-weed-or-cut-back-which-is-better
- quit-weed-regret-went-back
- quitting-weed-20s
- quitting-weed-30s
- quitting-weed-after-years
- quitting-weed-during-crisis-divorce-job-loss
- quitting-weed-exercise
- quitting-weed-grief-loss-coping
- quitting-weed-legal-state
- quitting-weed-success-stories
- quitting-weed-triggers-environment
- relapsed-smoking-weed-what-to-do
- relapsed-weed
- should-i-quit-weed
- sober-music-festival-concert-without-weed
- supplements-weed-withdrawal
- telling-friends-quitting-weed
- weed-relapse-prevention-plan
- weed-relapse-why-it-happens
- weed-ritual-replacement
- weed-ruined-relationships
- weed-social-media-triggers-quit
- pulled-over-with-weed-in-car
- cannabis-dui-laws-impairment-testing-penalties
- does-thc-affect-driving-impairment-science
Cite This Study
https://rethinkthc.com/research/RTHC-06126APA
Brubacher, Jeffrey R; Erdelyi, Shannon; Chan, Herbert; Simmons, Sarah; Atkinson, Paul; Besserer, Floyd; Clarke, David B; Davis, Phil; Daoust, Raoul; Émond, Marcel; Eppler, Jeff; Lee, Jacques S; MacPherson, Andrew; Magee, Kirk; Mercier, Eric; Ohle, Robert; Parsons, Mike; Rao, Jagadish; Rowe, Brian H; Taylor, John; Vaillancourt, Christian; Wishart, Ian. (2025). Prevalence of Impairing Substance Use in Injured Drivers.. JAMA network open, 8(4), e256379. https://doi.org/10.1001/jamanetworkopen.2025.6379
MLA
Brubacher, Jeffrey R, et al. "Prevalence of Impairing Substance Use in Injured Drivers.." JAMA network open, 2025. https://doi.org/10.1001/jamanetworkopen.2025.6379
RethinkTHC
RethinkTHC Research Database. "Prevalence of Impairing Substance Use in Injured Drivers." RTHC-06126. Retrieved from https://rethinkthc.com/research/brubacher-2025-prevalence-of-impairing-substance
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.