Improving the debate on cannabis. The effects of cannabis on driving are difficult to evaluate.

In their article on the cannabis debate, Strang et al raise the issue of cannabis and its effects on driving, suggesting that “a clearer understanding will be required of the extent to which a particular concentration of the drug (or its metabolites) can reliably be taken as evidence that an individual's driving ability was consequently impaired.” A review of the literature, however, suggests that defining an acceptable level of cannabis consumption for driving is unlikely to be possible for several reasons.