To describe electronic cigarette (e-cigarette) use and cigarette use among adolescents and determine whether established risk factors for smoking discriminate user categories.METHODS: School-based survey of 1941 high school students (mean age 14.6 years) in Hawaii; data collected in 2013. The survey assessed e-cigarette use and cigarette use, alcohol and marijuana use, and psychosocial risk and protective variables (eg, parental support, academic involvement, smoking expectancies, peer smoking, sensation seeking). Analysis of variance and multinomial regression examined variation in risk and protective variables across the following categories of ever-use: e-cigarette only, cigarette only, dual use (use of both products), and nonuser (never used either product).RESULTS: Prevalence for the categories was 17% (e-cigarettes only), 12% (dual use), 3% (cigarettes only), and 68% (nonusers). Dual users and cigarette-only users were highest on risk status (elevated on risk factors and lower on protective factors) compared with other groups. E-cigarette only users were higher on risk status than nonusers but lower than dual users. E-cigarette only users and dual users more often perceived e-cigarettes as healthier than cigarettes compared with nonusers.CONCLUSIONS: This study reports a US adolescent sample with one of the largest prevalence rates of e-cigarette only use in the existing literature. Dual use also had a substantial prevalence. The fact that e-cigarette only users were intermediate in risk status between nonusers and dual users raises the possibility that e-cigarettes are recruiting medium-risk adolescents, who otherwise would be less susceptible to tobacco product use. WHAT'S KNOWN ON THIS SUBJECT:There is a debate about whether e-cigarettes will benefit public health. However, there is little knowledge about how e-cigarette users and dual users (those using both e-cigarettes and tobacco cigarettes) differ from other adolescents on a range of variables. WHAT THIS STUDY ADDS:Teenagers who only used e-cigarettes were intermediate in levels of risk and protective factors between nonusers and those who used both cigarettes and e-cigarettes. This raises a question about whether e-cigarettes recruit low-risk youth to tobacco product use.

Objective Use of electronic cigarettes (e-cigarettes) is prevalent among adolescents, but there is little knowledge about the consequences of their use. We examined, longitudinally, how e-cigarette use among adolescents is related to subsequent smoking behaviour. Methods Longitudinal school-based survey with a baseline sample of 2338 students (9th and 10th graders, mean age 14.7 years) in Hawaii surveyed in 2013 (time 1, T1) and followed up 1 year later (time 2, T2). We assessed e-cigarette use, tobacco cigarette use, and psychosocial covariates (demographics, parental support and monitoring, and sensation seeking and rebelliousness). Regression analyses including the covariates tested whether e-cigarette use was related to the onset of smoking among youth who had never smoked cigarettes, and to change in smoking frequency among youth who had previously smoked cigarettes. Results Among T1 never-smokers, those who had used e-cigarettes at T1 were more likely to have smoked cigarettes at T2; for a complete-case analysis, adjusted OR=2.87, 95% CI 2.03 to 4.05, p<0.0001. Among ever-smokers at T1, using e-cigarettes was not related to significant change in their frequency of smoking at T2. Uptake of e-cigarette use among T1 never-users of either product was predicted by age, Caucasian or Native Hawaiian (vs Asian-American) ethnicity, lower parental education and parental support, higher rebelliousness and perception of e-cigarettes as healthier. Conclusions Adolescents who use e-cigarettes are more likely to start smoking cigarettes. This result together with other findings suggests that policies restricting adolescents’ access to e-cigarettes may have a rationale from a public health standpoint.