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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).

Comments:

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

Reference:

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.

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