Associations Between Parental and Grandparental Marijuana Use and Child Substance Use Norms in a Prospective, Three-Generation Study

PurposeUsing prospective longitudinal data from three generations, this study seeks to test whether and how parent and grandparent marijuana use (current and prior) predicts an increased likelihood of child cigarette, alcohol, and marijuana use.MethodsUsing multilevel modeling of prospective data spanning three generations (n = 306 families, children ages 6–22), this study tested associations between grandparent (G1) and parent (G2) marijuana use and child (G3) past-year cigarette, alcohol, and marijuana use. Analyses tested whether G3 substance-related norms mediated these associations. Current G1 and G2 marijuana use was examined, as was G2 high school and early adult use and G1 marijuana use when G2 parents were in early adolescence. Controls included G2 age at G3 birth, G2 education and depression, and G3 gender.ResultsG2 current marijuana use predicted a higher likelihood of G3 alcohol and marijuana use but was not related to the probability of G3 cigarette use. G3's perceptions of their parents' norms and G2 current marijuana use both contributed independently to the likelihood of G3 alcohol and marijuana use when included in the same model. G3 children's own norms and their perceptions of friends' norms mediated the link between G2 current marijuana use and G3 alcohol and marijuana use.ConclusionsResults are discussed in light of the growing trend toward marijuana legalization. To the extent that parent marijuana use increases under legalization, we can expect more youth to use alcohol and marijuana and to have norms that favor substance use.