Electronic cigarettes and future marijuana use: A longitudinal study

BACKGROUND: Cigarettes have been strongly associated with subsequent marijuana use among adolescents, but electronic cigarettes (e-cigarettes) are now rapidly replacing traditional cigarettes among youth. This study examines associations between youth e-cigarette use and subsequent marijuana use in a national sample. METHODS: Youth (aged 12-17 years) never marijuana users at wave 1 (n = 10 364; 2013-2014) from the Population Assessment of Tobacco and Health study were followed-up in 1 year (wave 2, 2014-2015). Multivariable logistic regressions were performed to evaluate associations between e-cigarette use at wave 1 and ever/heavy marijuana use in the past 12 months (P12M) and at wave 2. RESULTS: Among never marijuana users, e-cigarette ever use (versus never use) at wave 1 was associated with increased likelihood of marijuana P12M use (adjusted odds ratio [aOR] = 1.9; 95% confidence interval [CI]: 1.4-2.5) at wave 2. There was a significant interaction between e-cigarette use and age (P < .05) with aOR = 2.7 (95% CI: 1.7-4.3) for adolescents aged 12 to 14 and aOR = 1.6 (95% CI: 1.2-2.3) for adolescents aged 15 to 17. The association with heavy marijuana use was significant among younger adolescents (aOR = 2.5; 95% CI: 1.2-5.3) but was not among older adolescents. Heavier e-cigarette use at wave 1 yielded higher odds of P12M and heavy marijuana use at wave 2 for younger adolescents. CONCLUSIONS: E-cigarette use predicts subsequent marijuana use among youth, with a stronger associations among young adolescents. Reducing youth access to e-cigarettes may decrease downstream marijuana use.