Differences in the Association between Use of Electronic Vaping Products and Subsequent Tobacco and Marijuana Use among US Youth

Limited evidence shows that e-cigarette use is associated with subsequent cigarette and marijuana use among US adolescents. However, it remains unclear whether these associations differ by individual characteristics and state-level policies. This dissertation examines effect modification of biological sex on the association between e-cigarette use and subsequent cigarette use (Study One), effect modification of mental health conditions on the association between e-cigarette use and subsequent marijuana use (Study Two), and effect modification of state recreational marijuana laws on the association between e-cigarette use and subsequent marijuana use (Study Three). Data were compiled from the first four waves (2013-2018) of the Population Assessment of Tobacco and Health (PATH) Study. Wave 1 to 3 were each considered as the baseline for its corresponding 12-month follow-up wave. The study population included adolescents (aged 12-17) who reported never using cigarettes or marijuana at baseline. Generalized estimating equations (GEE) were used to evaluate the associations and effect modifications. Study One found that among baseline never cigarette smokers, baseline past-30-day e-cigarette use was significantly associated with past-30-day cigarette smoking at follow-ups. This association was significantly stronger for boys (aOR=6.17, 95% CI: 2.43–15.68) than for girls (aOR=1.10, 95% CI: 0.14–8.33). Study Two found that baseline e-cigarette use was significantly associated with marijuana use at 12-month follow-ups. Adolescents with severe internalizing (IMH) or externalizing mental health (EMH) problems were significantly more likely to initiate marijuana use. Additionally, e-cigarette users who reported more severe IMH symptoms were less likely to initiate marijuana use (aOR=3.04, 95% CI: 1.20–7.74), compared with those with less severe IMH problems (aOR=10.15, 95% CI: 4.72–21.81). Study Three found that the association between baseline past-30-day e-cigarette use and past-30-day marijuana use at follow-ups was significantly stronger for adolescents in states that legalized adult recreational marijuana use (aOR=18.39, 95% CI: 4.25–79.68) than those in states without such laws (aOR=5.09, 95% CI: 2.86–9.07). The findings highlighted that efforts to curb youth cigarette and marijuana initiation may benefit from efforts to reduce youth vaping. Tailored interventions characterized by individual demographics and state policies are warranted for e-cigarette using adolescents