A developmental‐based motivational intervention to reduce alcohol and marijuana use among non‐treatment‐seeking young adults: a randomized controlled trial.

Abstract: Aims: To test the hypothesis that among non‐treatment‐seeking emerging adults (EA) who both use marijuana and have alcohol binges, a brief, longitudinally delivered, developmentally based motivational intervention would show greater reductions in the use of these two substances compared with a health education control condition. Design: Parallel, two‐group, randomized controlled trial with follow‐up interventions conducted at 1, 3, 6 and 9 months and final assessments at 12 and 15 months. Setting: Hospital‐based research unit in the United States. Participants: Community‐based 18–25‐year‐olds who reported at least monthly binge drinking and at least weekly marijuana use. Intervention: Motivational intervention (EA‐MI) focused primarily on themes of emerging adulthood (identity exploration, instability, self‐focus, feeling in‐between, a sense of possibilities) and the subjects' relationship to substance use ( n  = 110) compared with an attention‐matched health education control condition ( n  = 116). Measurements: The primary outcomes were days of binge alcohol, marijuana and dual use day as measured using the timeline follow‐back method analysing the treatment by time interaction to determine relative differences in the rate of change between intervention arms. Findings: At baseline, the mean rate (days/30) of binge drinking was 5.23 (± 4.31) of marijuana use was 19.4 (± 10.0) and of dual (same day) use was 4.11 (± 4.13). Relative to baseline, there were reductions in the rate of binge alcohol use, marijuana use and days of combined binge alcohol and marijuana use ( P  < 0.001) at all follow‐up assessments. However, the treatment × time interaction was not statistically significant for alcohol ( P  = 0.37), for marijuana ( P  = 0.07) or for dual use ( P  = 0.55). Averaged over all follow‐ups, mean reductions in binge, marijuana and dual use days were 1.16, 1.45 and 1.08, respectively, in the health education arm, and 1.06, 1.69 and 0.96 in EA‐MI. Bayes factors were < 0.01 for frequency of binge alcohol use and frequency of dual binge alcohol and marijuana and 0.016 for marijuana use. Conclusions: A brief, longitudinally delivered, developmentally based motivational intervention for young adults did not produce reductions in binge alcohol, marijuana use or dual use days relative to a control condition. [ABSTRACT FROM AUTHOR]