Marijuana as a predictor of concurrent substance use among motor vehicle operators.

Despite the adverse effects associated with marijuana abuse and dependence, marijuana is becoming more common-place in activities such as driving. Previous literature has discussed the high rates of cocaine, opioid and benzodiazepine use among users of marijuana, but no research has addressed the rates of concurrent use among drivers meeting abuse or dependence criteria. Each of these substances may produce effects detrimental to driving safety which may be compounded by concurrent substance use. This research examines rates of marijuana use, abuse, and dependence among an active sample of drivers (N = 7,734) in the 2007 National Roadside Survey. Mean age of participants was 36.89 years, and the majority were male (60.1%) and identified as White (59.2%). Participants who used marijuana but did not meet diagnostic criteria for abuse (n = 165) or dependence (n = 112) were significantly more likely to test positive for all substances than were those who did not use marijuana. Further, those that met criteria for marijuana abuse or dependence were more likely than those who did not meet criteria to test positive for THC, cocaine, and benzodiazepines and THC, cocaine, and opioids, respectively. The current research has implications for policy development and drugged driving interventions.