Although many schools perform preventive interventions for reducing drug use, little is known about their implementation processes and results. Accordingly, this study aimed to evaluate the effectiveness of three different types of preventive intervention performed in the school setting for reducing substance use among students. The study comprised 1316 students from the 9th year of elementary school to the 3rd year of secondary school in 8 public schools in the city of Guarulhos, São Paulo state, Brazil. Students were randomly assigned to the intervention groups or a control group and were evaluated at two different time-points regarding substance use. The results indicated that interventions performed by teachers were most effective in reducing both substance use and the severity of substance-associated problems. Interventions performed by experts were partially effective, although they only reduced use among experimental users. The results of “Single lecture” interventions revealed that such approaches are counterproductive. In summary, preventive actions that were contextualized to the student's reality and the school environment and that included the active involvement of both teacher and student were most effective at reducing the prevalence of substance use and the severity of associated problems in students.
Drug abuse; Adolescents; Prevention; Teachers; Randomized clinical trial