Objective: For many substances, more frequent and problematic use occurs in young adulthood; these types of use are predicted by the timing of initiation during adolescence. We replicated and extended an earlier study examining whether delayed substance initiation during adolescence, resulting from universal preventive interventions implemented in middle school, reduces problematic use in young adulthood.
Method: Participants were middle school students from 36 Iowa schools randomly assigned to the Strengthening Families Program: For Parents and Youth 10-14 (Molgaard, Spoth, & Redmond, 2000) plus Life Skills Training (LST; Botvin, 1995, 2000), LST-only, or a control condition. Self-report questionnaires were collected at 11 time points, including 4 during young adulthood. The intercept (average level) and rate of change (slope) in young adult frequency measures (drunkenness, alcohol-related problems, cigarettes, and illicit drugs) across ages 19-22 were modeled as outcomes influenced by growth factors describing substance initiation during adolescence. Analyses entailed testing a 2-step hierarchical latent growth curve model; models included the effects of baseline risk, intervention condition assignment, and their interaction.
Results: Analyses showed significant indirect intervention effects on the average levels of all young adult outcomes, through effects on adolescent substance initiation growth factors, along with Intervention × Risk interaction effects favoring the higher risk subsample. Additional direct effects on young adult use were observed in some cases. Relative reduction rates were larger for the higher risk subsample at age 22, ranging from 5.8% to 36.4% on outcomes showing significant intervention effects.
Conclusions: Universal preventive interventions implemented during early adolescence have the potential to decrease the rates of substance use and associated problems into young adulthood.