Event-level influences of alcohol, cannabis, and simultaneous use on perceived driving risk

Alcohol-impaired driving is highly prevalent and a leading cause of death. Cannabis is commonly used among people who drink alcohol, and using alcohol and cannabis simultaneously is associated with a greater frequency of alcohol-impaired driving. Laboratory studies demonstrate the harmful effects of simultaneous use on driving ability compared to alcohol use alone, yet driving under the influence of cannabis is perceived as a low risk. We tested the influences of alcohol, cannabis, and their simultaneous use on perceived driving impairment and willingness to drive in daily life. Participants were 88 adults aged 18-44 (M_age = 25.22 years, 60.2% female, 85.2% White) who reported using alcohol and cannabis simultaneously at least twice per week. They completed 14 days of ecological momentary assessment and reported their alcohol and cannabis use, perceived driving impairment, and willingness to drive "right now" and "1 hr from now" on an average of 5.14 surveys per day. Adjusting for the total amount of alcohol consumed, results from multilevel models include greater perceived driving impairment when using alcohol (b = 0.39, SE = 0.05, p < .001) and cannabis (b = 0.37, SE = 0.03, p < .001) separately, but greater odds of being willing to drive right now (OR = 2.29, 95% CI [1.38, 3.81], p = .001) and in 1 hr (OR = 3.69, 95% CI [2.15, 6.34], p < .001) when using alcohol and cannabis simultaneously compared to using alcohol by itself. Simultaneous use of cannabis may attenuate the impact of alcohol on the decision to drive and may contribute harmfully to in-the-moment decisions to drive under the influence of alcohol. (PsycInfo Database Record (c) 2025 APA, all rights reserved).