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Research Summary

Marijuana Use Is Associated with an Increased Risk of Motor Vehicle Accidents

This systematic review and meta-analysis examined the association between recent marijuana use and motor vehicle accidents (MVAs). Cohort studies with comparison groups and case-control studies published in any language were eligible for inclusion. The main outcome was fatal or nonfatal MVA. Recent cannabis use among drivers was determined by toxicological testing or self-report. Using a predefined search strategy, the authors identified 4 high-quality and 5 medium-quality studies using the Newcastle-Ottawa scale.

  • Six of 9 studies found a positive association between recent marijuana use and MVAs, while 3 of 9 found no association.
  • Odds ratios (ORs) for individual studies ranged from 0.82 to 7.2. The pooled OR for the association between recent marijuana use and MVAs was 1.9, but studies were heterogeneous.
  • The OR was 2.2 for high-quality studies and 1.8 for medium-quality studies.
  • The OR for fatal collisions was significant (2.1), but the OR for nonfatal collisions was not (1.7).


Overall, this study found an association between recent marijuana use and MVAs. Because of the heterogeneity of the studies, the pooled OR should not be considered a definitive estimate of risk. An additional limitation is the absence of data to assess a “dose” relationship between marijuana use and MVAs. Therefore, these results cannot offer guidance as to whether there is a safe threshold of marijuana use while driving.

Hillary Kunins, MD, MPH, MS


Asbridge M, Hayden JA, Cartwright JL. Acute cannabis consumption and motor vehicle collision risk: systematic review of observational studies and meta-analysis. BMJ. February 9, 2012;344:e536.