Perceived Friends' Use As a Risk Factor for Marijuana Use Across Young Adulthood

Introduction: Perceived social norms of substance use are commonly identified as a risk factor among adolescents and college students. However, the extent which these norms are developmentally strengthening or weakening as risk factors for marijuana use has not yet been documented. Typical models have constrained researchers to assuming that risk factors have particular effects that remain the same over time. However, changing associations between risk factors for substance use and behaviors are likely an important part of development. Therefore, the current analysis considers how the associations between perceived friends’ marijuana use and own marijuana use changes across young adulthood.

Method: Data are from the Monitoring the Future panel study from 1976-2014. Respondents included in this analysis were followed from ages 18 to 30 and reported marijuana use and perceived friends' use of marijuana for at least one time point. Analytic Ns range from 30,013 to 30,794, depending on the model (with 169,158 to 173,427 person-waves). The sample is 55% female, 75% White, 8% African American, 8% Hispanic and 9% Asian and other races; 69% of the sample report having parents with at least some college education. Time-varying effect modeling (TVEM) was used to examine the associations between perceived friends' use of marijuana and participants’ annual marijuana use from ages 18 to 30, as well as the extent to which these associations were moderated by gender, race/ethnicity, and parental education. 

Results: The prevalence of marijuana use and perceived friends’ use varied by age. Associations between perceived friends’ use and own marijuana use increased with age. In addition, the association between perceived friends’ use and own marijuana use significantly varied by demographic groups. The association between perceived friends’ use and own use was significantly greater among men from ages 19-24 and from ages 27-30, compared to women; for whites, compared to other race/ethnicities; and for individuals whose parents attended college, compared to those whose parents had a high school education or less, across all ages.

Conclusions: Results suggest that perceived friends’ marijuana use becomes an even more important marker for increased marijuana use as individuals age through young adulthood. Therefore, the role of peers in substance use remains increasingly important and should be incorporated into intervention strategies for young adults.