Twelve studies that evaluated 13 group treatments were included (n=1,663 participants).
None of the 13 treatments met the criteria for being efficacious. Two treatments (Psychoeducational Therapy and Adolescent Group Therapy) met criteria for being possibly efficacious as they had a comparison condition at seven- and 12-month assessments and both significantly reduced illicit substance use levels from baseline.
Eight other treatments showed statistically significant reductions in substance use from baseline to post-test or later follow-ups, but these were within-group changes and not compared to a control group.