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Published on: August 1, 2025
Marijuana use and motor vehicle crashes
Mu-Chen Li1, Joanne E Brady, Charles J DiMaggio
1Department of Anesthesiology, Columbia University College of Physicians and Surgeons, New York, New York 10032, USA.
Epidemiologic Reviews
|October 7, 2011
Summary
Marijuana use by drivers significantly increases the risk of motor vehicle crashes. This meta-analysis of 9 studies confirms a heightened crash risk associated with cannabis consumption, even after accounting for other factors.
Area of Science:
- Public Health
- Epidemiology
- Forensic Science
Background:
- Medical marijuana laws have been enacted in 16 US states and DC since 1996.
- Marijuana is the most frequently detected drug in impaired drivers, but its link to crash causation is debated.
Purpose of the Study:
- To conduct a meta-analysis assessing the association between marijuana use and motor vehicle crash risk.
- To synthesize findings from epidemiologic studies on cannabis and driving safety.
Main Methods:
- Systematic search of bibliographic databases for 9 relevant epidemiologic studies published in the last two decades.
- Meta-analysis using a random-effects model to pool odds ratios.
- Analysis of individual studies for confounding variables and dose-response relationships.
Main Results:
- The pooled odds ratio for crash involvement associated with marijuana use was 2.66 (95% CI: 2.07, 3.41).
- Heightened crash risk persisted after adjusting for confounding factors.
- Crash risk increased with higher concentrations of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol and self-reported frequency of marijuana use.
Conclusions:
- Driver marijuana use is significantly associated with an increased risk of motor vehicle crashes.
- Evidence suggests a dose-response relationship between marijuana use and crash involvement.
- Findings highlight public health concerns regarding impaired driving and cannabis legalization.
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