Supplementary Information
We present results of a randomized, controlled, efficacy trial of a handbook intervention for parents of first-year college students. The aim of the interactive intervention was to decrease risk behaviors by increasing family protective factors. The handbook, based in self-determination theory and the social development model, provided evidence-based and developmentally targeted suggestions for parents to engage with their students in activities designed to support successful adjustment to college. We recruited 919 parent-student dyads from incoming students enrolled at a university in the U.S. Pacific Northwest and randomly assigned them to control and intervention conditions. We sent handbooks to intervention parents in June before students’ August matriculation. Research assistants trained in motivational interviewing contacted parents to encourage use of the handbook. Control parents and students received treatment as usual. Participants completed baseline surveys during their final semester in high school (time 1) and their first semester at college (time 2). Self-reported frequency of alcohol, cannabis, and simultaneous use increased across both handbook and control students. In intent-to-treat analyses, odds of increased use were consistently lower and of similar magnitude for students in the intervention condition than in the control condition, and odds of first-time use were also lower in the intervention condition. Contact from research assistants predicted parents’ engagement, and parent and student report of active engagement with handbook predicted lower substance use among intervention than control students across the transition to college. We developed a low-cost, theory-based handbook to help parents support their young adult children as they transition to independent college life. Students whose parents used the handbook were less likely to initiate or increase substance use than students in the control condition during their first semester in college.ClinicalTrials.gov Identifier: NCT03227809The online version contains supplementary material available at 10.1007/s11121-023-01520-6.