Generational Changes in Adolescent Alcohol and Marijuana Use

Substance use during adolescence is a significant predictor of developing a later substance use disorder. An encouraging trend is that there have been recent declines in rates of adolescent substance use, including alcohol and marijuana. However, these two substances may be decreasing differently from one another as a result of age, period, and cohort effects. Therefore, the overall trend of decreased substance use in more recent generations of adolescents may be greater for one substance than the other. The current study tested declines in adolescent alcohol and marijuana use across two generations measured in 1988-1990 and 2006-2012. Methodological strengths include controls for demographic characteristics and for parental alcohol disorder (as a proxy for genetic risk). Moreover, we tested whether findings would replicate using two methods—first comparing all assessed members of one generational cohort with all assessed members of the other generational cohort, and then comparing only matched parent-child pairs. Testing this second matched sample removes some potential demographic and risk confounds that might occur across cohorts in typical epidemiological studies. Results demonstrated that the younger cohort of adolescents used both substances less than the older cohort, and this effect was stronger for alcohol than for marijuana. These results were replicated in both samples over and above demographic variables. The parent-child sample showed that children used less alcohol and marijuana than did their parent during the same age period, suggesting that these trends cannot simply be due to changes in the demographics of the adolescent population over time. Taken together with epidemiological studies, these findings suggest encouraging declines in adolescent substance use rates but also indicate less decline in marijuana use compared to alcohol use. This prompts further surveillance to determine if marijuana use rates may start increasing among adolescents in the future.