Grant: Operating Grant

Alcohol and cannabis are the psychoactive substances most often found in seriously and fatally injured drivers. We recently observed that individuals who reported both driving under the influence of alcohol (DUIA) and of cannabis (DUIC) experienced collision risk nearly 4 times that of individuals who reported DUIA or DUIC alone. Residual or 'hangover' effects of either substance on road safety are not well understood but may be substantial. In a recent study, drivers with alcohol hangover but no other evidence of substance use constituted 18% of a group of police-identified suspected impaired drivers. In our ongoing study of cannabis effects on driving, we have seen preliminary evidence of residual effects up to 48 hours following cannabis use. To date, little information on the combined effects of alcohol and cannabis is available, and the residual effect of combined use has not been examined. This study will examine the acute effects of alcohol and cannabis on driving and the residual effects 24 hours later. Fifty subjects aged 19 to 25 will complete 8 experimental sessions (2 sessions/week). Each week subjects will complete one session with alcohol/drug exposure and simulated driving trial and one session 24 hours later with driving trial only. The order of alcohol/drug conditions will be randomly assigned and will include: 1) placebo cannabis/placebo alcohol, 2) placebo cannabis/alcohol, 3) cannabis/placebo alcohol, and 4) cannabis/alcohol. The target blood alcohol content will be 0.08%. A single dose of cannabis will be administered at 12.5% ± 2% THC. Subjects will be social drinkers and regular users of cannabis, but not heavy/problem users, and must be free of health concerns that would contraindicate use of alcohol or cannabis. Effects on mood and cognition will also be assessed. Studies show that cannabis and alcohol are often used together by young drivers. Identifying factors that affect the collision risks of this population is a public health priority.