Marijuana-using drivers, alcohol-using drivers, and their passengers: prevalence and risk factors among underage...

Driving after marijuana use increases the risk of a motor vehicle crash. Understanding this behavior among young drivers and how it may differ from alcohol-related driving behaviors could inform prevention efforts.

To describe the prevalence, sex differences, and risk factors associated with underage college students' driving after using marijuana, driving after drinking alcohol, or riding with a driver using these substances.

Cross-sectional telephone survey of a random sample of 315 first-year college students (aged 18-20 years) from 2 large public universities, who were participating in an ongoing longitudinal study. At recruitment, 52.8% of eligible individuals consented to participate; retention was 93.2% one year later when data for this report were collected.

Self-reported past-28-day driving after marijuana use, riding with a marijuana-using driver, driving after alcohol use, and riding with an alcohol-using driver.

In the prior month, 20.3% of students had used marijuana. Among marijuana-using students, 43.9% of male and 8.7% of female students drove after using marijuana (P < .001), and 51.2% of male and 34.8% of female students rode as a passenger with a marijuana-using driver (P = .21). Most students (65.1%) drank alcohol, and among this group 12.0% of male students and 2.7% of female students drove after drinking (P = .01), with 20.7% and 11.5% (P = .07), respectively, reporting riding with an alcohol-using driver. Controlling for demographics and substance use behaviors, driving after substance use was associated with at least a 2-fold increase in risk of being a passenger with another user; the reverse was also true. A 1% increase in the reported percentage of friends using marijuana was associated with a 2% increased risk of riding with a marijuana-using driver (95% CI, 1.01-1.03). Among students using any substances, past-28-day use of only marijuana was associated with a 6.24-fold increased risk of driving after substance use compared with using only alcohol (95% CI, 1.89-21.17).

Driving and riding after marijuana use is common among underage, marijuana-using college students. This is concerning given recent legislation that may increase marijuana availability.