The Influence of Parent and Grandparent Marijuana Use on Child Substance Use: What Might We Expect If Adult Use Increases Under Legalization?

Prevention of youth marijuana use is an important public health priority. Effective prevention may be complicated by the growing trend toward legalization of adult recreational marijuana use among U.S. states. Substance use by known adults, especially parents and grandparents, has been identified repeatedly as an important predictor of youth substance use. Using prospective data spanning three generations (G1 grandparents, G2 parents, G3 children), this study tested associations between G1 and G2 marijuana use and G3 marijuana, cigarette, and alcohol use. Current G1 and G2 marijuana use were included, as were G1 and G2 marijuana use before G3 was born (called historical use). Historical use was included to test whether, for example, marijuana use by G2 parents during important periods in their own development (e.g., the transition to adulthood) was related to later substance use by G3.

Data were drawn from the Seattle Social Development Project (SSDP) and The SSDP Intergenerational Project (TIP). Participants included 383 youth ranging in age from 6-22, their parents, and one of their grandparents. Multilevel models included repeated measures (across 7 data collection waves) of G3 past year marijuana, cigarette, and alcohol use, and tested whether these G3 behaviors were predicted by time-varying measures of G1 and G2 current marijuana use and time-fixed measures of G2 historical marijuana use (during high school; at ages 21-24) and G1 historical marijuana use (when G2 were ages 13-14). Controls included G1 and G2 current cigarette and alcohol use, G2 education, and G3 gender. G3 child age was treated as the “time” variable to model the developmental pattern of youth substance use and to account for the accelerated longitudinal design of the study.

Results showed that G2 current marijuana use predicted a higher likelihood of child past year marijuana and alcohol use. G2 current cigarette use predicted a higher likelihood of G2 marijuana and cigarette use. G1 current substance use was unrelated to G3 substance use, as were G1 and G2 historical marijuana use.

The present results suggest that parent current marijuana use predicts an increased risk for marijuana and alcohol use among their children. To the extent that marijuana legalization is associated with an increase in the prevalence or frequency of marijuana use among parents, we can expect to see increased rates of marijuana and alcohol use among youth. The current findings also highlight the importance of continued efforts to reduce cigarette use among parents, as parent current smoking predicted both child cigarette and marijuana use.