INTRODUCTION: The objective of this study was to examine the mechanisms of social influence driving e-cigarette use in adolescent social networks and differentiate between the effects of exposure to friend behavior and social norms on individual use. METHODS: Surveys on health behaviors and friendship networks from nine high schools in Southern California (N = 2,245
48% Hispanic) were collected at three time points from Spring 2021 of grade 9, Fall 2021, and Spring 2022 of grade 10. Stochastic actor-oriented models for the co-evolution of social networks and behavior dynamics tested for friendship network social influences on e-cigarette use. Two mechanisms of social influence were estimated, exposure to friend behavior (e-cigarette use among friends) and pro-e-cigarette social norms (perceived peer approval and use of e-cigarettes), while controlling for social selection, individual covariates, and endogenous network effects. Results from the nine schools were combined in a meta-analysis. RESULTS: Findings revealed social influence effects through exposure to friend e-cigarette use and pro-e-cigarette social norms, which both had significant positive influences on individual e-cigarette initiation over time. Further, Hispanic/Latine individuals and females were more likely to initiate e-cigarette use compared to males and non-Hispanic/Latine students. CONCLUSIONS: The importance of these effects should be considered in tobacco prevention initiatives. Designing culturally tailored interventions that target youth social networks and e-cigarette social norms could be effective at curtailing adolescent use. Changing perceptions and social acceptability of e-cigarettes could be one way to slow or prevent the spread of e-cigarette use in adolescent networks. IMPLICATIONS: These findings demonstrate the role of social influence on adolescent e-cigarette use through two mechanisms, both friend behavior and social norms. A shift in prevention strategies toward addressing social dynamics and social norms rather than focusing solely on individual level factors may be effective in curtailing use. Changing social perceptions and reducing he social acceptability of e-cigarette use may help slow the spread in adolescent networks.