Alcohol and Marijuana Use Trajectories in a Diverse Longitudinal Sample of Adolescents

AIMS: We tested race/ethnic differences in alcohol and marijuana (AM) trajectories (comprising an intercept term, reflecting overall probability of use, and a slope term, reflecting change in probability of use) during adolescence, whether AM use trajectories predicted high school outcomes, and whether outcomes differed by race/ethnicity after controlling for trajectory of AM use. DESIGN: This longitudinal study involved 6509 youth from 16 middle schools in Southern California surveyed from age 11.5 (2008) to age 17 (2015) years; all surveys assessed AM use, and the final survey also examined high school outcomes. SETTING: Youth completed five surveys in middle school and two on-line surveys in high school. PARTICIPANTS: The sample was 50% male and 80% non-white. MEASUREMENTS: Intercept (at 2.75 years post-baseline) and slope of AM use were examined as outcomes for race/ethnic differences. AM use trajectories were examined as predictors of academic performance and unpreparedness, social functioning, mental and physical health and delinquency. FINDINGS: We found differences in trajectories of use by race/ethnicity, with white youth reporting a higher overall intercept of alcohol use compared to all other groups (versus Asian P < 0.001, black P = 0.001, multi-ethnic P = 0.008). Overall, examination of trajectories of use showed that adolescents with a higher alcohol use intercept term reported greater academic unpreparedness (P < 0.001) and delinquency (P < 0.001) at wave 7 in high school. In addition, youth with a higher intercept for marijuana use reported greater academic unpreparedness (P < 0.001) and delinquency (P < 0.001), and poorer academic performance (P = 0.032) and mental health (P = 0.002) in high school. At wave 7, compared to white youth, Hispanic and multi-ethnic youth reported poorer academic performance (P < 0.001 and P = 0.034, respectively); Asian, black and Hispanic youth reported higher academic unpreparedness (P < 0.001, P = 0.019, and P = 0.001); and Asian youth and multi-ethnic youth reported poorer physical health (P = 0.012 and P = 0.018) controlling for AM use. CONCLUSIONS: Greater AM use was associated with worse functioning in high school for all youth. After controlling for AM use, non-white youth reported worse outcomes in high school for academics and health.