Deterioration over time in effect of Motivational Interviewing in reducing drug consumption and related risk among young people.

AIM: To test whether beneficial effects of a single session of Motivational Interviewing (MI) on alcohol, tobacco and illicit drug use apparent after 3 months were maintained until 12 months. DESIGN: Cluster randomized trial, allocating 200 young people in the natural groups in which they were recruited to either MI (n = 105) or to an assessment-only control condition (n = 95). SETTING: Ten further education colleges across inner London. PARTICIPANTS: Two hundred young people who were current users of illegal drugs (age range 16-20 years) with whom contact was established through peers trained for the project. INTERVENTION: The intervention was adapted from MI in the form of a topic-based 1-hour single-session discussion. MEASUREMENTS: Changes in cigarette, alcohol, cannabis and other drug use and perceptions of risk and harm between the time of recruitment and follow-up interviews after 3 and 12 months. FINDINGS: A satisfactory follow-up rate (81%) was achieved. After 12 months, 3-month differences between MI and assessment-only groups have disappeared almost entirely. Unexpected improvements by the assessment-only control group on a number of outcomes suggest the possibility of reactivity to the research assessment at 3-month follow-up. CONCLUSION: In the terms of the original experiment, there is little evidence of enduring intervention effectiveness shown by between-group differences after 12 months. Deterioration of effect is the most probable explanation, although reactivity to 3-month assessment, a late Hawthorne effect, cannot be ruled out.