Age of First Use as a Predictor of Current Alcohol and Marijuana Use Among College-Bound Emerging Adults

Background: Alcohol and marijuana are the most commonly used psychoactive substances; however, the sequencing and relationship between age of first use and continued current problematic use among college-bound emerging adults is not well understood. Methods: This is a cross-sectional study of current and historical alcohol and marijuana use among college-bound recent high school graduates (N=1,365; age approximate to 18 years). Results: Drinking was prevalent (78%, N=1,055) and marijuana use was prevalent (46%, N=622). Stepwise logistical regression revealed the lower the age of first use, the higher the prevalence of current problematic substance use. Those who initiate alcohol12 are twice as likely to currently use marijuana frequently. A significant relationship was found between age of first use and non-social substance use (drinking, p=0.0001; marijuana, p=0.0025). The temporal ordering of substance use indicates that alcohol precedes marijuana use, and age of first alcohol use is relevant to rates of initiation and current marijuana use.