RESEARCH REPORT © 2005 Society for the Study of Addiction doi:10.1111/j.1360-0443.2005.01013.x Addiction, 100, 470–478 Blackwell Science, LtdOxford, UKADDAddiction0965-2140© 2005 Society for the Study of Addiction 100 Original Article Maintenance of MI effects over time Jim McCambridge & John Strang Correspondence to: Jim McCambridge Addiction Sciences Building 4 Windsor Walk Denmark Hill London SE5 8AF UK E-mail: J.McCambridge@iop.kcl.ac.uk Submitted 8 March 2004; initial review completed 24 June 2004; final version accepted 24 November 2004 RESEARCH REPORT Deterioration over time in effect of Motivational Interviewing in reducing drug consumption and related risk among young people Jim McCambridge & John Strang National Addiction Centre (The Maudsley/Institute of Psychiatry), London, UK ABSTRACT Aim To test whether beneficial effects of a single session of Motivational Inter- viewing (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. KEYWORDS Alcohol, brief intervention, cannabis, cigarette smoking, drugs, Motivational Interviewing, young people. INTRODUCTION There have now been more than four decades of research in which the ‘irrepressible dream of addiction prevention’ has been pursued through primary prevention, with a great deal of societal investment (DuPont 1998). Even with the most effective primary preventive interventions, effect sizes are small and many young people will make decisions to initiate and to continue to use drugs (Coggans et al. 2003). For this reason, there is a need to develop secondary prevention among young people already involved in drug use. Brief interventions have been developed for this purpose among adults, most nota- bly in reducing alcohol consumption (Moyer et al. 2002). Motivational Interviewing (MI) is a client-centred and directive counselling style, with an increasingly broad evidence base (Miller & Rollnick 1991, 2002). In 1997, Noonan & Moyers (1997) conducted the first formal