Trajectories of E-Cigarette and Conventional Cigarette Use Among Youth.

Background: Electronic cigarette (e-cigarette) use is common among youth, and there are concerns that e-cigarette use leads to future conventional cigarette use. We examined longitudinal associations between past-month cigarette and e-cigarette use to characterize the stability and directionality of these tobacco use trajectories over time.

Methods: High school students ( = 808, 53% female) completed surveys across 3 waves (2013, 2014, and 2015) in 3 public schools in Connecticut. Using autoregressive cross-lagged models, we examined bidirectional relationships between past-month cigarette and e-cigarette use over time. Models were adjusted for covariates related to tobacco use (ie, sex, race/ethnicity, socioeconomic status, and use of other tobacco products).

Results: Past-month e-cigarette use predicted future cigarette use (wave 1-2: odds ratio [OR] = 7.08, 95% confidence interval [CI] = 2.34-21.42; wave 2-3: OR = 3.87, 95% CI = 1.86-8.06). However, past-month cigarette use did not predict future e-cigarette use (wave 1-2: OR = 2.02, 95% CI = 0.67-6.08; wave 2-3: OR = 1.90, 95% CI = 0.77-4.71). Additionally, frequency of cigarette and e-cigarette use increased over time. By wave 3, 26% of cigarette users and 20.5% of e-cigarette users reported using 21-30 days out of the past month.

Conclusions: E-cigarette use was associated with future cigarette use across 3 longitudinal waves, yet cigarette use was not associated with future e-cigarette use. Future research needs to examine mechanisms through which e-cigarette use leads to cigarette use. E-cigarette regulation and prevention programs may help prevent future use of cigarettes among youth.