The mediating factors of a school-based intervention to prevent substance use in adolescence

Adolescent substance use is still one major concern in Western countries. During the last twenty years, advances in prevention field have been made and some program seems to be effective in preventing youth from drug use in late adolescence and adulthood. Particularly, the programs based on enhancement of individual competencies and on social influence theory seem to be promising in the prevention of drug abuse. In spite of the advancement in knowledge, there are still many unanswered questions. One important limitation concerns the mediating mechanisms of successful interventions. There is a lack of knowledge about the mediation mechanisms through which interventions have an effect. The present study attempts to answer this question, by investigating the mediated factors of a European school-based intervention (Unplugged) that has shown to decrease alcohol and tobacco use in the short terms. The program consisted in 12-hour class-based curriculum based on a 100 comprehensive social-influence approach. Data were collected in seven European countries. 7,079 pupils 12-14 years of age were randomly assigned to one of three experimental conditions or to a control condition. All the groups filled out a questionnaire before the intervention (pre-test), and three months after the end of the program (post-test). Multilevel regression models were used. Results showed that a decrease of perception of benefits associated to the use is a mediator of the program effect on tobacco and alcohol use. This study shed light on the possible mechanisms through which school-based interventions work.