PURPOSE: This two-arm cluster randomized controlled trial evaluated the effectiveness of an app-based addiction prevention program in German vocational school students. METHODS: Schools from 5 German federal states were recruited. No eligibility criteria for classes were applied
enrollment decisions were made by school heads or teachers. Students were eligible if aged at least 16 years and possessing a smartphone (participation rate: 46.7%). Classes were randomly allocated to intervention or control within blocks of 4, stratified by school. Intervention classes received app-based coaching for 16 weeks. Control classes received health information and could access the coaching after 12 months. Both groups were assessed at baseline, 6 months, 6 and 12 months (follow-up rates: 35.8% and 34.9%). Primary outcomes were changes in alcohol, tobacco, cannabis consumption, and problematic Internet use at the individual level. Participants were blinded to group allocation until providing informed consent
the primary outcome analyst was also blinded. Generalized linear models with multiple imputation were used across all time points. RESULTS: Intention-to-treat analyses of 1,266 intervention and 1,279 control participants from 162 classes each showed small but significant effects on social competence (b = 0.075, confidence interval [CI] 0.027, 0.123
d DISCUSSION: App-based programs can reduce addictive behaviors and enhance life skills among vocational students, fostering broader mental health benefits.