The Acute and Residual Effects of Cannabis on Driving and the Risk of Collision for People who Drive after using Alcohol and Drive after using Cannabis

Although the impairing effects produced by alcohol and their direct effect on the driving task have been well defined for decades, similar information on the effects of Δ9-tetrahydrocannabinol (THC) following cannabis use in relation to driving skill is lacking. A combination of experimental and epidemiological studies is presented that examine the effects of THC on driving and collision risk. Preliminary data from a driving simulation study explores how THC impairs driving ability both acutely and residually and consideration is given to the challenges faced when conducting this type of research. Epidemiological data from a population-level survey demonstrate that the self-reported concurrent behaviours of driving under the influence of alcohol (DUIA) and driving under the influence of cannabis (DUIC) impart an increased risk of past-year collision more than 3 times greater than reporting driving after using a single substance, or not driving following substance use.MAS