Objective: This meta-analytic review assesses the effectiveness of substance abuse interventions to reduce adolescent cannabis use. Method: A systematic search identified 15 randomized controlled evaluations of interventions to reduce adolescent cannabis use published between 1960 and 2008. The primary outcome variables, frequency of cannabis use, and quantity of cannabis use, were measured between 1 month and 1 year posttreatment completion. Results: Analyses of random effects models revealed similarly moderate effects for individual (g = -0.437; 95% CI = [-0.671, -0.203]) and family-based treatments (g = -0.404; 95% CI = [-0.613, -0.195]). Substance abuse treatments are associated with moderate reductions in cannabis use although effect sizes tended to wane with greater length of time posttreatment. Discussion: Substance abuse treatment programs should consider implementing evidence-based interventions highlighted in this meta-analysis that fit the needs and characteristics of their client base and agency setting. (Contains 1 figure and 3 tables.)