Effect modification of legalizing recreational cannabis use on the association between e-cigarette use and future cannabis use among US adolescents

Background: Many states have legalized recreational cannabis use for adults. However, no study has examined how this policy may interact with youth vaping to influence cannabis use among US adolescents. This study investigates whether the association between baseline e-cigarette use and subsequent cannabis use differs by state recreational cannabis legalization status. Methods: This study analyzed data from the first four waves (2013–2018) of the Population Assessment of Tobacco and Health Study, a nationally representative longitudinal survey. The study sample included adolescents (aged 12–17) who reported never used cannabis at baseline. Generalized estimating equations were used to analyze the effect modification of state recreational cannabis law on the association between baseline e-cigarette use and cannabis use at 12-month follow-up, controlling for individual characteristics. Results: Among adolescents who have never used cannabis at baseline, baseline past-30-day e-cigarette use was significantly associated with past-30-day cannabis use at 12-month follow-up (aOR=5.92, 95% CI: 3.52–9.95). This association was different by state recreational cannabis legalization status, as indicated by the significant interaction term. Subgroup analysis showed that the aOR was 18.39 (95% CI: 4.25–79.68) for adolescents living in states that legalized adult recreational cannabis use and 5.09 (95% CI: 2.86–9.07) for adolescents living in states without such laws. Conclusions: E-cigarette use is associated with cannabis initiation among youth. This association is stronger among those living in states that legalized adult recreational cannabis use. Further examination of the impact of e-cigarette use on cannabis initiation in relation to state cannabis laws is warranted