Longitudinal associations between e-cigarette use and onset of multiple modes of cannabis use among US adolescents

•Youth e-cigarette use was associated with onset of multiple modes of cannabis use.•Association between e-cigarette and cannabis vaping was not stronger than others.•Non-Hispanic black youth were more likely to blunt or smoke cannabis with hookah.•Adult recreational cannabis legalization was associated with youth cannabis use. To examine the prospective associations between e-cigarette use and subsequent onset of various modes of cannabis use during a 12-month follow-up period among US adolescents. Data were from the Wave 4 (2017, baseline) and Wave 4.5 (12-month follow-up) surveys of the Population Assessment of Tobacco and Health (PATH) Study, a nationally representative, longitudinal cohort study. Study population was cannabis-naïve US adolescents (12–16 years) at baseline who reported cannabis use status at follow-up (N = 9,692). Outcomes were modality-specific past-12-month cannabis use (vaping, blunting, smoking with hookah) and any cannabis use (past-12-month and past-30-day) at follow-up. Multivariate logistic regressions were used to estimate the weighted association between baseline past-30-day e-cigarette use and each outcome. Baseline e-cigarette use was significantly associated with onset of cannabis vaping (aOR = 4.00, 95% CI = 2.25–7.10), blunting (aOR = 5.30, 95% CI = 2.82–9.94), any cannabis use (aOR = 3.94, 95% CI = 2.35–6.62), and past-30-day cannabis use (aOR = 4.47, 95%CI = 2.64–7.58) at follow-up. Non-Hispanic blacks were more likely to report past-12-month blunting (aOR = 1.55, 95% CI = 1.07–2.24) and smoking cannabis with hookah (aOR = 3.13, 95% CI = 1.14–8.63) compared with non-Hispanic whites. Other tobacco use, alcohol use, perceiving e-cigarette use as having little or some harm, older age, high severity of externalizing mental health problems, and living in states legalized adult recreational cannabis use were significantly associated with future onset of cannabis vaping, blunting, and any cannabis use. The association of e-cigarette use with cannabis vaping was not stronger than its association with other modes of cannabis use. Future studies are needed to explain the mechanisms linking e-cigarettes and cannabis use.