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.