Factors Mediating the Effectiveness of the Unplugged School-Based Prevention Program

Background. 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. Objectives. The present study aimed to investigate factors mediating the effects of the European school-based social influence intervention "Unplugged" on youths' substance use. Methods. Schools in seven European countries (n=143, including 7079 pupils) were randomly assigned to an experimental (Unplugged curriculum) or to a control condition (usual health education). Data was collected before (pre-test) and three months after the end of the program (post-test). Multilevel multiple mediation models were applied to the study of effect mediation, separately for tobacco, alcohol, and cannabis use. Analyses were conducted on the whole sample, and separately on baseline users and non-users of each substance. Results. Compared to the control group, participants in the program endorsed less positive attitudes toward drugs, positive beliefs about cigarettes, alcohol, and cannabis, and the normative perception of peers using tobacco and cannabis. They also increased in knowledge about all substances and refusal skills towards tobacco. Decreased positive attitudes towards drugs, increase in refusal skills and reappraisal of norms about peer using tobacco and cannabis appeared to mediate the effects of the program on the use of substances. However, mediating effects were generally weak and some of them only marginally significant. Conclusions. Results of the study suggest that positive attitudes towards drugs, normative perceptions of use among peers, and refusal skills might explain most of the effectiveness of interventions based on social influence. On the other hand, targeting other mediators, such as beliefs or knowledge, may not contribute to the effectiveness of such programs. These results should be taken into account to build up new cost-effective prevention interventions.