Driving while under the influence of cannabis

The findings of the linked paper by Asbridge and colleagues (doi:10.1136/bmj.e536) add weight to the argument that cannabis users should be deterred from driving while intoxicated because of the risk of injury or death to themselves and others.1 This systematic review of nine case-control studies and culpability studies found that recent cannabis use almost doubled the odds of having a motor vehicle crash (odds ratio 1.92, 95% confidence interval 1.35 to 2.73). The increased risk was marginally larger in better designed studies (2.21 v 1.78), in case-control rather than culpability studies (2.79 v 1.65), and in studies that examined deaths rather than injuries (2.10 v 1.74). The authors note that, although residual confounding is possible, their results are consistent with experimental evidence that cannabis use leads to dose related impairments in simulated driving, psychomotor skills, and on-road driving.2 3

Public health education about the dangers of driving while under the influence of cannabis is unlikely to be enough to deter cannabis users from driving—they will …