A cluster randomized trial on the effects of a parent and student intervention on alcohol use in adolescents four years after baseline; no evidence of catching-up behavior.

Objective: It is questioned whether the alcohol prevention program "Prevention of Alcohol use in Students" (PAS) is effective in reducing the prevalence of heavy weekend drinking and the amount of drinking among adolescents at the age at which they are allowed to buy alcohol in The Netherlands (16 years). In addition, it is questioned whether the intervention effects are attributed to a delay in onset earlier in adolescence or to the development of skills due to the PAS intervention (mediation analyses).

Design: A cluster randomized trial including 3490 Dutch early adolescents (M age=12.66, SD=0.49) and their parents randomized over four conditions; 1) parent intervention, 2) student intervention, 3) combined intervention and 4) control group.

Outcome Measures: Outcome measures were prevalence of heavy drinking and amount of weekend drinking measured at age 16, 50 months after baseline.

Results: Only when parents and students were targeted simultaneously could the prevalence of heavy weekend drinking (b=-.44, p=.02) and the amount of alcohol use (b=-.24, p=.02) be reduced. No significant effects of the separate parent and student interventions were found. The effect of the combined PAS intervention on heavy weekend drinking and amount of drinking can be attributed to respectively the increase in self-control and strict parenting, and a delayed alcohol initiation earlier in adolescence.

Conclusions: The current study confirms the effectiveness of the combined PAS intervention up to the legal drinking age of 16. The results underline that postponing the onset of drinking among early adolescents is not only crucial for health development in the short term, but also impacts the development of a healthier drinking pattern later on.