Randomized controlled trial of motivational interviewing compared with drug information and advice for early intervention among young cannabis users.

AIM: To test the effectiveness of motivational interviewing (MI) in comparison with drug information and advice in opportunistically securing reductions in drug-related risk among young cannabis users not seeking help. DESIGN: Randomized controlled trial. SETTING: Eleven London Further Education colleges. PARTICIPANTS: A total of 326 students aged 16-19 years who smoked cannabis weekly or more frequently. INTERVENTIONS: Participants were randomized to a single-session intervention of MI or drug information and advice-giving. MEASUREMENTS: Cannabis use, cigarette smoking and alcohol consumption and harm outcomes were assessed after both 3 and 6 months. FINDINGS: No differences were found between MI and drug information and advice, although MI fidelity was not high. There were wide-ranging individual practitioner effects on observed outcomes and a practitioner-intervention interaction was detected in relation to cannabis cessation after 3 months. Change over time was more pronounced for cannabis use than for other drug use. CONCLUSIONS: Further study of the nature and consequences of MI fidelity, and individual practitioner effects more generally, is needed. Advice may be an effective brief intervention with young cannabis users in its own right and should be evaluated further in trials.