Effectiveness of Motivational Incentives for Adolescent Marijuana Users in a School-Based Intervention

Purpose: This study examined whether adolescents receiving Motivational Interviewing (MI) intervention have different outcomes compared to those receiving Motivational Incentives (Motivational Interviewing combined with Contingency Management; MI + CM). Method: A total of 136 adolescents (from a parent study of 220 adolescents) with problematic substance use were recruited from 8 high schools in Washington State, where they completed either 8-weeks of MI or MI + CM. Frequency of marijuana use was assessed at baseline, at the end-of-treatment, and at 16-week follow-up. Results: A balanced and matched sample was created using propensity scores, then analyzed using Hierarchical Linear Modeling (HLM). Multilevel regression analyses revealed that adolescents who received MI + CM exhibited a greater reduction in use across time (p < .05). Reductions at the end-of-treatment were greater for the MI + CM condition (Cohen's d = -.82) compared to MI alone (Cohen's d = -.33), but did not differ at 16-week follow-up. Adolescents receiving MI + CM showed significantly fewer negative consequences of marijuana use at the end-of-treatment (t1, 124 = 2.26, p < .05), higher use of coping strategies (t1, 124 = 3.01, p < .01), and increased likelihood to attend additional treatment for substance use (chi 2 1,124 = 4.12 p < .05), though hypothesized improvements in motivation and school attendance were not found. Use of coping strategies at the end-of-treatment had a significant indirect effect on the relationship between the intervention condition and marijuana use at the end-of-treatment (F3, 121 = 10.20, R2 = .20, p < .01). Conclusion: These results suggest that the inclusion of contingencies into adolescent marijuana treatment decreases the end-of-treatment frequency of marijuana use and related consequences while increasing the use of coping strategies and the pursuit of additional treatment. (C) 2015 Elsevier Inc. All rights reserved.