Marijuana Use and Motor Vehicle Crashes

Since 1996, 16 states and the District of Columbia in the United States have enacted legislation to decriminalize marijuana formedical use.Althoughmarijuana is themost commonlydetectednonalcohol drug indrivers, its role in crash causation remains unsettled. To assess the association between marijuana use and crash risk, the authors performed a meta-analysis of 9 epidemiologic studies published in English in the past 2 decades identified through a systematic search of bibliographic databases. Estimated odds ratios relating marijuana use to crash risk reported in these studies ranged from0.85 to7.16.Pooledanalysisbasedon the random-effectsmodel yieldedasummaryodds ratioof 2.66 (95% confidence interval: 2.07, 3.41). Analysis of individual studies indicated that the heightened risk of crash involvement associatedwithmarijuanausepersistedafter adjustment for confoundingvariablesand that the risk of crash involvement increased in a dose-response fashionwith the concentration of 11-nor-9-carboxy-delta-9-tetrahydrocannabinol detected in theurineand the frequencyof self-reportedmarijuanause.The resultsof thismeta-analysis suggest thatmarijuanause by drivers is associated with a significantly increased risk of being involved in motor vehicle crashes. accidents, traffic; automobiles; cannabis; motor vehicles; substance abuse detection Abbreviations: THC, delta-9-tetrahydrocannabinol; THC-COOH, 11-nor-9-carboxy-THC. In the United States, marijuana possession and use were banned by the Controlled Substances Act of 1970; however