Associations between Simultaneous and Co-Occurring Use of Alcohol and Marijuana and Risky Driving Perceptions and Behaviors

Background: Co-occurring use of alcohol and marijuana (co-use) and simultaneous use of alcohol and marijuana (SAM use) have been linked to a host of negative outcomes including traffic accidents and driving while intoxicated. The present study examined associations among alcohol-only use, co-use (but not SAM use), SAM use, and risky driving perceptions and behaviors. Methods: Participants included a subsample of 507 young adults (18-23 at screening) participating in a longitudinal study examining social role transitions and substance use. Data for present analyses come from Month 18 measures including past month alcohol and marijuana use, SAM use, and the DRIVE questionnaire, which includes 11 items assessing risky driving perceptions and 16 items assessing risky driving behaviors. Participants also reported on past-month having “driven a car when I knew I had too much to drink to drive safely” and/or “drove a car or other vehicle within three hours of using cannabis whether or not you still felt high.” Dummy variables were coded for past month SAM use or co-use, with alcohol-only use comprising the reference group. A small percentage of participants used marijuana only in the past month and are not included in analyses. Logistic and multivariate regression analyses were conducted examining associations among SAM use, co-use, and risky driving perceptions and behaviors, controlling for participant gender and age. Results: Descriptively, 23% reported SAM use, 14% co-use, and 63% consumed only alcohol in the past month. Relative to alcohol-only, SAM use was positively associated with overall risky driving perceptions and perceiving that driving after smoking marijuana is relatively safe. Co-use was not associated with measures of perceived risky driving. Relative to alcohol-only use, SAM use was positively associated with general risky driving behaviors, driving within three hours of using marijuana, and driving after having too much to drink; co-use was positively associated with driving within three hours of using marijuana, relative to alcohol-only use. Conclusions: Findings highlight SAM use as a correlate of risky driving perceptions and behaviors in general and driving while under the influence of alcohol and marijuana among young adults. Education about driving-related risks associated with SAM use and prevention efforts targeting young adults who engage in SAM use are needed. Among college students, brief motivational personalized feedback interventions have been found to reduce alcohol consumption and marijuana use and thus may be an effective strategy for reducing SAM use and associated risks.