Efficacy of a Mobile Phone-Based Life-Skills Training Program for Addiction Prevention Optimized Among Adolescents With Low Program Engagement: Cluster-Randomized Controlled Trial.

Background: Previous studies demonstrated the effectiveness of SmartCoach, a mobile phone-based life-skills training program for addiction prevention among adolescents. However, socially stratifying factors, such as educational level or migration background, were associated with lower program engagement and participation. To address these disparities, we optimized and tailored program elements, particularly for subgroups with low engagement, using qualitative interview data. Objective: This study aimed to test whether the optimized program version was superior to the original one in terms of efficacy and program use. We hypothesized that optimization and advanced tailoring would result in increased program efficacy and engagement. Methods: A 2-arm, parallel-group, double-blind, cluster-randomized controlled trial was conducted with assessments at baseline and follow-up after 6 months. Secondary and upper secondary school classes were randomized into two groups: (1) an intervention group receiving the optimized program version and (2) a control group receiving the original version. Participants in both groups received up to 4 weekly SMS text messages over 4 months to stimulate (1) self-management skills to cope with stress, (2) self-efficacy to resist social pressure, (3) observational learning, and (4) self-regulation. The optimized program version included additional reminders, extended time for challenges, simplified language, different days for weekly messages, and additional tailoring for participants with personal or parental backgrounds from non-German-speaking countries. This subgroup received shorter video clips and information on additional stressors, including acculturation and family conflicts. The primary outcomes of this trial were the quantity of alcohol use, the number of days per month that nicotine-containing products were smoked, and cannabis use days. Results: A total of 1175 students from 67 Swiss secondary and upper secondary school classes were invited to participate in the study between September 2023 and September 2024. Of these 1175 students, 890 (75.7%; mean age 14.9, SD 1.3 y; women: n=511, 57.4%; men: n=379, 42.6%; nonbinary: n=0, 0.0%) participated in the study. Six-month follow-up assessments were completed by 552 (62.0%) of the 890 study participants. On average, program use did not differ between the study groups, with 12.6 (SD 12.8) of 38 possible activities completed in the intervention group and 12.5 (SD 12.7) activities in the control group (P=.18). The results concerning efficacy showed no significant differences between the study groups regarding the main outcomes of alcohol use quantity (P=.91), nicotine use days (P=.45), and cannabis use days (P=.67). Similarly, no significant group differences were observed for changes in perceived stress (P=.77) and social skills (P=.45). Conclusions: The results did not show improved program use or efficacy in the optimized version of the program. Possible explanations include the relatively minor differences between the 2 program versions and the generally low prevalence rates of substance use in this age group, which limited the statistical power of the study.