Investigating Moderation in the Prospective Relationship of Marijuana Use to Subsequent Illicit Substance Use: Evidence from Add Health

Abstract

While socially normalized substances (e.g., marijuana) may increase the probability of subsequent progression to more harmful illicit substances, previous empirical research on the topic has yielded inconsistent results. Few studies have prospectively examined whether age of first documented current marijuana use is related to later harmful illicit substance use over multiple life course stages, or considered potential moderation of the process by age of first documented current marijuana use, gender, or race/ethnicity. To investigate this topic, data from five waves the National Longitudinal Study of Adolescent to Adult (N=20,774), spanning ages 12-42, were used to analyze the prospective association of current marijuana use at any of the five waves to current illicit substances in early middle adulthood (i.e., Wave 5), conditional on sociodemographic controls. Moderation in the effect of first documented current marijuana use on later illicit substance use was tested for three putative moderators, gender, race/ethnicity, and age of first reported current marijuana use, using interaction effects. Multiple imputation was used to address a modest amount of missing data. Results indicate that current marijuana use at any wave was strongly associated with documented current illicit substance use in early middle adulthood (OR=4.506, p p