It all depends

This commentary discusses the issue and many aspects of motivational interviewing with cannabis users. The randomized trial by McCambridge et al. meets a high methodological standard and contributes a null finding for motivational interviewing (MI) with adolescent cannabis users. It is common for the efficacy of MI to vary across studies, among sites within multi-site trials and across clinicians providing MI within a study. MI, on average, yields small to medium effect sizes relative to control and comparison conditions, and clarification of the reasons for this variability in outcomes could improve the fidelity and efficacy of MI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)