Factors mediating the effectiveness of a school-based intervention to prevent substance use in adolescence (“Unplugged”)

Adolescents’ substance use is still a major concern in Western countries. During the last twenty years, advances in prevention field have been made and some programs have been shown as effective in preventing youth from drug use in late adolescence and adulthood. Particularly, programs based on enhancement of individual competences and on social influence theory seem to be promising. In spite of the advancement in knowledge, there are still many unanswered questions, e.g. the mediation mechanisms through which interventions work. The present study aimed at investigating factors mediating the effects on tobacco, cannabis use and alcohol abuse of a European school-based intervention (Unplugged) that has been shown to decrease alcohol and tobacco use in the short term. The program consisted of 12-hour curriculum based on a social-influence approach. 143 schools (7079 pupils) of seven European countries were randomly assigned to experimental or control condition. Data was collected before and three months after the end of the program. Multilevel multiple mediators models were performed to study mediators of the effects on tobacco, cannabis use and drunkenness episodes, for users and abstainer at baseline. Participants in the program decreased positive attitudes toward drugs, positive beliefs about cigarettes, alcohol, and cannabis, and the normative perception of peers actually involved in tobacco and cannabis use. They also increased negative beliefs about tobacco, knowledge and refusal skills towards all substances compared to control group. Positive attitudes towards drugs, refusal skills and perception of peer using tobacco and cannabis mediated the effects of the program on the use of substances.