Gender differences in the developmental trajectories of multiple substance use and the effect of nicotine and marijuana use on heavy drinking in a high-risk sample

Background: Heavy drinking is highly comorbid with nicotine and marijuana use among young adults. Yet, our knowledge about the longitudinal effects of nicotine and marijuana use (including onset timing and quantity/frequency) on heavy drinking and whether the effects vary by gender is very limited. This study aims to characterize gender-specific developmental trajectories of multiple substance use and to examine gender differences in the effects of nicotine and marijuana use on heavy drinking. Methods: We conducted secondary analysis on 8 waves of data from 850 high-risk youth who were recruited as ninth graders with low GPA in an economically disadvantaged school district in the Midwest and were followed up annually to young adulthood. Onset ages and quantity/frequency of multiple substance use were assessed by a self-report questionnaire at each wave. The time-varying effect model and linear mixed model were adopted for statistical analysis. Results: Males' levels of heavy drinking, nicotine use, and marijuana use tended to grow persistently from adolescence to emerging adulthood. Females, on the other hand, only gradually increased their nicotine use across time while maintaining low levels of heavy drinking and marijuana use. Controlling for the early onset status of alcohol use, early onset statuses of nicotine use and marijuana use both added additional risk for heavy drinking; late onset marijuana users were also at higher risk for heavy drinking than nonusers of marijuana. Controlling for substance use onset statuses, higher quantity/frequency of nicotine and marijuana use both contributed to more involvement in heavy drinking. We also found that the effect of nicotine use quantity on heavy drinking was greater among males. Conclusions: Our study demonstrates the longitudinal effects of onset timing and quantity/frequency of nicotine and marijuana use on heavy drinking. Oar analysis of gender differences also identifies female youth's nicotine use and male youth's co-use of nicotine and alcohol as two important areas for future prevention and intervention work. (C) 2015 Elsevier Ltd. All rights reserved.