This study explored secondary effects of a multisite randomized alcohol prevention trial on tobacco, marijuana, and other illicit drug use among a sample of incoming college students who participated in high school athletics. Students (n = 1,275) completed a series of Web-administered measures at baseline during the summer before starting college and 10 months later. Students were randomized to one of four conditions: a parent-delivered intervention, a brief motivation enhancement intervention (Brief Alcohol Screening and Intervention for College Students [BASICS]), a condition combining the parent intervention and BASICS, and assessment-only control. A series of analyses of variance evaluating drug use outcomes at the 10-month follow-up assessment revealed significant reductions in marijuana use among students who received the combined intervention compared to the BASICS-only and control groups. No other significant differences between treatment conditions were found for tobacco or other illicit drug use. Our findings suggest the potential utility of targeting both alcohol and marijuana use when developing peer- and parent-based interventions for students transitioning to college. Clinical implications and future research directions are considered.