IMPORTANCE Adolescents are exposed to e-cigarette and cannabis content on social media. Understanding associations of these exposures with use and dual use of these products can guide regulations.

OBJECTIVE To assess whether adolescent exposure to e-cigarette and/or cannabis content on social media, including posts by various content creators, is associated with e-cigarette, cannabis, and dual use.

DESIGN, SETTING, AND PARTICIPANTS Two surveys, one longitudinal (study 1, baseline in 2021 to 2022) and one cross-sectional (study 2, fall 2023), were conducted among California high school students who completed questionnaires on computers in classrooms.

EXPOSURES In study 1, the baseline was frequent exposure (weekly or more vs less frequent or none) to e-cigarette and/or cannabis social media posts. In study 2, the exposure (yes vs no) was to e-cigarette and/or cannabis posts from specific sources (friends, celebrities, microinfluencers, e-cigarette and/or cannabis brands, or unknown sources).

MAIN OUTCOMES AND MEASURES For study 1, the primary outcome was solo e-cigarette, solo cannabis, or dual use initiation at 1-year follow-up among baseline never-users of e-cigarettes and cannabis. For study 2, the primary outcome was past-month use of e-cigarettes, cannabis, and dual use. Generalized estimating equations models adjusted for sociodemographic characteristics, mental health, other tobacco product use, social media use, and social environment.

RESULTS In study 1, of 4232 adolescents (mean [SD] age, 17.0 [0.6] years; 2205 female [52.1%]), 968 (22.9%) reported frequent baseline exposure to e-cigarette posts and 507 (12.0%) reported exposure to cannabis posts on social media, broadly; 567 (13.4%) were frequently exposed to e-cigarette posts specifically on TikTok. Frequent exposure to cannabis social media posts was associated with solo e-cigarette use (adjusted odds ratio [AOR], 1.83; 95% CI, 1.11-3.01), solo cannabis use (AOR, 1.60; 95% CI, 1.07-2.38), and dual use (AOR, 1.71; 95% CI, 1.11-2.63) initiation at 1-year follow-up. Frequent exposure to e-cigarette posts on TikTok was associated with solo cannabis use (AOR, 1.74; 95% CI, 1.17-2.58) and dual use (e-cigarette and cannabis) initiation (AOR, 1.78; 95% CI, 1.19-2.66). In study 2, of 3380 adolescents (mean [SD] age, 17.0 [0.6] years; 1840 female [54.4%]), 195 (5.8%) were exposed to microinfluencer e-cigarette posts, and 152 (4.5%) were exposed to microinfluencer cannabis posts; 151 (4.5%) were exposed to friends' e-cigarette posts, and 161 (4.8%) were exposed to friends' cannabis posts. Exposure to e-cigarette (AOR, 2.67; 95% CI, 1.55-4.59) and cannabis (AOR, 2.14; 95% CI, 1.15-4.00) microinfluencer posts was associated with past-month cannabis use. Exposure to friends' e-cigarette posts was associated with past-month dual use (AOR, 2.53; 95% CI, 1.24-5.19), whereas exposure to friends' cannabis posts was associated with past-month cannabis use (AOR, 3.35; 95% CI, 1.94-5.78) and dual use (AOR, 2.46; 95% CI, 1.28-4.71).

CONCLUSIONS AND RELEVANCE In this survey study of California adolescents, exposure to e-cigarette or cannabis posts was associated with adolescent e-cigarette, cannabis, or dual use. Improvement of social media community guidelines and greater policy attention to co-use and marketing of e-cigarettes and cannabis may help prevent youth substance use.