Six-month follow-up of the ‘Mi Mejor Plan’ school-based prevention program: a pilot cluster randomized controlled trial among early adolescents in Chile

BMC Public Health. 2026 Jul 21. doi: 10.1186/s12889-026-28548-x. Online ahead of print.

ABSTRACT

BACKGROUND: School-based preventive interventions for adolescent substance use often show limited short-term behavioral effects, with evidence suggesting that sustained impacts may depend on continued exposure and reinforcement strategies such as booster sessions. However, few studies have examined the longitudinal effects of booster implementation on substance use and related psychosocial outcomes in culturally adapted interventions.

METHODS: We conducted a cluster randomized controlled trial to evaluate the longitudinal impact of a culturally adapted school-based prevention program among sixth-grade adolescents (mean age 11.3 years) in Chile. Schools assigned to the intervention received a 16-session curriculum and three booster sessions, whereas control schools continued with treatment-as-usual prevention activities. Assessments were conducted at baseline, immediately post-intervention, and approximately six months later following completion of the booster sessions. Primary outcomes were substance use behaviors (30-day prevalence of tobacco, alcohol, and cannabis), while secondary outcomes included cognitive and social determinants. Mixed-effects models were used to assess changes over time, accounting for clustering at the school level.

RESULTS: A total of 765 students from 11 schools were enrolled, with 608 assessed at baseline and 426 at follow-up. While no significant reductions in substance use were observed immediately post-intervention, longitudinal analyses indicated improvements in selected secondary outcomes, including more negative beliefs about tobacco and alcohol and enhanced decision-making processes. Several cognitive and social determinants remained improved at the assessment conducted after completion of the booster sessions. An increase in positive beliefs about marijuana was also observed at follow-up. However, effects on behavioral outcomes remained limited across time points.

CONCLUSIONS: Several cognitive and social determinants of substance use remained improved at follow-up despite the absence of significant behavioural effects. Longer-term studies are needed to determine whether these changes translate into reductions in substance use.

TRIAL REGISTRATION: ClinicalTrials.gov, number NCT04236947; registration date: 17/01/2020. Available at: https://clinicaltrials.gov/ct2/show/NCT04236947.

PMID:42477638 | DOI:10.1186/s12889-026-28548-x