Preventing heavy alcohol use in adolescents (PAS): cluster randomized trial of a parent and student intervention offered separately and simultaneously Ina M. Koning 1,2 , Wilma A. M. Vollebergh 2 , Filip Smit 1,3 , Jacqueline E. E. Verdurmen 1 , Regina J. J. M. van den Eijnden 2 , Tom F. M. ter Bogt 2 , Håkan Stattin 5 & Rutger C. M. E. Engels 4 Trimbos Institute, Netherlands Institute of Mental Health and Addiction, Utrecht, the Netherlands, 1 Department of Interdisciplinary Social Science, Utrecht University, Utrecht, the Netherlands, 2 Institute of Extra-Mural Medicine (EMGO), VU Medical Centre, Amsterdam, Amsterdam, the Netherlands, 3 Behavioural Science Institute, Radboud University Nijmegen, Nijmegen, the Netherlands 4 and Center for Developmental Research, Örebro University, Örebro, Sweden 5 ABSTRACT Aims To evaluate the effectiveness of two preventive interventions to reduce heavy drinking in first- and second-year high school students. Design and setting Cluster randomized controlled trial using four conditions for comparing two active interventions with a control group from 152 classes of 19 high schools in the Netherlands. Participants A total of 3490 first-year high school students (mean 12.68 years, SD = 0.51) and their parents. Intervention conditions (i) Parent intervention (modelled on the Swedish Örebro Prevention Program) aimed at encouraging parental rule-setting concerning their children’s alcohol consumption; (ii) student intervention consisting of four digital lessons based on the principles of the theory of planned behaviour and social cognitive theory; (iii) interventions 1 and 2 combined; and (iv) the regular curriculum as control condition. Main outcome measures Incidence of (heavy) weekly alcohol use and frequency of monthly drinking at 10 and 22 months after baseline measurement. Findings A total of 2937 students were eligible for analyses in this study. At first follow-up, only the combined student–parent intervention showed substantial and statistically significant effects on heavy weekly drinking, weekly drinking and frequency of drinking. At second follow-up these results were replicated, except for the effects of the combined intervention on heavy weekly drinking. These findings were consistent across intention-to-treat and completers-only analyses. Conclusions Results suggest that adolescents as well as their parents should be targeted in order to delay the onset of drinking, preferably prior to onset of weekly drinking. Keywords Alcohol use, cluster randomized trial, early adolescents, parents, prevention, separately, simulta- neously, weekly drinking. Correspondence to: Ina M. Koning, Department of Interdisciplinary Social Science, Utrecht University, PO Box 80.140, 3508TC Utrecht, the Netherlands. E-mail: i.koning@uu.nl Submitted 2 February 2009; initial review completed 29 April 2009; final version accepted 7 May 2009 INTRODUCTION Alcohol use of Dutch adolescents ranks among the highest in Europe [1]. At the age of 13, two out of three adolescents in the Netherlands have had their first drink and one out of five have been drunk at least once in their life [2]. A lower age of onset is associated with a greater risk of alcohol abuse 10 years later [3]. Also, each addi- tional year of delayed drinking reduces the likelihood of dependence by 14% [4]; therefore, from a public health viewpoint, prevention of alcohol use in young adoles- cents is crucial. Recently, the importance of targeting not only children, but also their parents has been established clearly. Parents play a pivotal role when it comes to pro- viding access to alcohol for early adolescents. Further, when parents set restrictive rules about alcohol use, their offspring are more likely to postpone drinking [5–7]. Thus, to discourage alcohol use in early adolescents, it is imperative to consider both adolescents and their parents in interventions. Although there is little evidence for the effectiveness of student interventions alone [8–11], some studies show promising results [10,11]. However, interventions target- ing parents appear to be even more promising [12]. A RESEARCH REPORT doi:10.1111/j.1360-0443.2009.02677.x © 2009 The Authors. Journal compilation © 2009 Society for the Study of Addiction Addiction, 104, 1669–1678