Few studies have examined the co-occurrence of alcohol and marijuana use in clinical samples of young adults. The present study investigated whether co-occurring marijuana use is associated with characteristics indicative of a high level of risk in young adult heavy drinkers. Individuals between the ages of 18 and 25 years (N=122) participated in an ongoing 8-week randomized clinical trial that tested the efficacy of placebo-controlled naltrexone plus brief individual counseling to reduce heavy drinking. At intake participants completed self-report assessments on alcohol consumption, alcohol-related negative consequences, motivation to reduce drinking, trait impulsivity, expectancies for alcohol-induced disinhibition, use of cigarettes, and history of medication nonadherence. In univariate tests heavy drinkers with and without co-occurring marijuana use did not differ on alcohol consumption, most alcohol-related negative consequences, and motivation to reduce drinking. In multivariate tests controlling for demographic characteristics, co-occurring heavy alcohol and marijuana use was significantly associated with nonplanning impulsivity (β=2.95) and a history of both unintentional (adjusted odds ratio [aOR]=3.30) and purposeful (aOR=3.98) nonadherence to medication. Findings suggest that young adult heavy drinkers with co-occurring marijuana use exhibit a high-risk clinical profile and may benefit from interventions that increase adherence to medications.
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