Empirical Evidence for Reducing Adolescent Marijuana Use: New Findings from the Adolescent Substance Abuse Treatment Database

Background and Purpose: More than one-third of high school seniors report having used marijuana in the previous year (Johnston, O'Malley, Bachman, & Schulenberg, 2008). The detrimental effects of adolescent marijuana use, while often minimized, include serious physical, mental and social consequences. Adolescent marijuana use places youth at increased risk for dropping out of high school, delinquency, and unemployment into adulthood (Brooke, Blaka, & Whiteman, 1999). While individual interventions have been rigorously tested for their ability to reduce adolescent marijuana use, this study presents a meta-analysis that is among the first to synthesize effects across intervention studies. Conducted by the authors in 2009, the findings from this rigorous meta-analysis will provide a clear synthesis of the latest empirical information in the field of marijuana use reduction.

Methods: This study utilized the Adolescent Substance Abuse Treatment Database (ASAT-D), an ongoing effort to identify, synthesize, and disseminate the most current intervention knowledge for adolescent substance abusers. This systemized search of the literature (1960-2008) identified 15 random clinical trials and 2 quasi-experimental studies of interventions to reduce adolescent marijuana use. Pooled effects of standardized mean differences (Hedges's g) were utilized to synthesize data across studies meeting search criteria. Stratified analyses compared effects for individual verses family-based interventions. Further, sensitivity analyses were conducted to assess publication bias and file drawer effects on study results.

Results: Pooled effects indicated interventions to reduce adolescent marijuana use have a moderate effect (Hedges's g = .544, p<.001). Stratified analyses revealed similarly moderate effects for individual (g = -0.542) and family-based treatments (g = -.557). While treatment effects decreased with longer follow up periods, several interventions demonstrated significant reductions in marijuana use at 12 months post treatment. In addition, the authors identified several interventions with large effect sizes. This includes previously supported interventions, such as Integrated Family and Cognitive Behavior Therapy, Multidimensional Family Therapy, and Motivational Interviewing, but also introduces innovative interventions such as Teaching Family – an intervention targeting youth and their group home parents.

Conclusions: Our results indicate that existing interventions significantly reduce adolescent marijuana use. When addressing adolescents' use of marijuana, individual and family-based interventions are both moderately effective. As the field of social work is consistently responsible for treating adolescent substance users, social work practitioners and social work educators should be aware of the latest empirical evidence regarding the effectiveness of established interventions. Particularly social workers employed in substance abuse treatment and prevention programs should be aware of the impact of interventions to specifically address marijuana use and, where risk is identified, implement evidence-based interventions highlighted in this meta-analysis.