Parental practices as mediators of the effect of a family-based program on the prevention of substance use among Brazilian adolescentes

•Evidence-based family programs reduce alcohol use and binge drinking in adolescents, with parenting mediating this effect.•Evidence-based Family programs may reduce susbtance use by increasing parental responsiveness and demandingness.•Though not directly impacting adolescents, it is important to assess how family programs influence parents in preventing substance use.•Investigating evidence-based family programs is crucial in preventing substance use, emphasing parental practices. Evidence-based family prevention programs aims at strengthening family relationships and for reducing substance use. Thus, this study aims to evaluate the mediating effect of parental practices in reducing the prevalence of lifetime alcohol, cigarette, and inhalant use among adolescents enrolled in a family-based program. A cluster-randomized controlled trial was conducted in Social Assistance Reference Centers of 12 Brazilian municipalities to verify the effectiveness of the Famílias Fortes program. The sample included 1610 participants from 805 families, with each family nucleus consisting of one adolescent aged 10 to 14 years and one of their parents or guardians. The intervention group participated in seven meetings led by previously trained facilitators. The control group did not receive any interventions to prevent substance use. Data were collected at baseline, 6 and 12 months. Four mediation models were conducted, assessing the effect of the program according to the combined influence of parental practices on each outcome: adolescents’ lifetime use of alcohol, cigarettes, inhalants, and the practice of binge drinking. The combination of all parental behaviors tested was found to act as a mediator of the effect of Famíilias Fortes in reducing lifetime alcohol use and binge drinking. The mediation model also showed that the program had an indirect effect in the reduction of cigarette and inhalant use by increasing parental responsiveness and demandingness. Although the program did not directly influence adolescents, it effectively prevented substance use by positively influencing parental actions, which indirectly influenced substance use behaviors in adolescents.