Adolescent Dual Use Classification and Its Association With Nicotine Dependence and Quit Intentions

Purpose: Electronic cigarettes (e-cigarette) use is rapidly increasing in the U.S., especially among adolescents. A significant number of adolescents use both cigarettes and e-cigarettes, often referred to as dual use. We used a new classification of dual use, taking into account the frequency of use of both products. In addition, we examined the association between dual use with time to first cigarette after waking (a nicotine dependence measure) and quit intention. Methods: Data were drawn from the 2015–2018 National Youth Tobacco Survey. We grouped participants by dual use frequency. Multivariable logistic regression was used to examine the association of dual use frequency with nicotine dependence and quit intention. Results: Different categories of dual users varied in demographic characteristics and beliefs on the harms of cigarette smoking and e-cigarette use. Compared with cigarette-only smokers, significantly higher odds of nicotine dependence were found for high-frequency e-cigarette dual users (within 5 minutes of awakening, odds ratio [OR]: 1.67, 95% confidence interval [CI], 1.07–2.62; within 30 minutes, OR: 1.61, 95% CI, 1.15–2.27), high-frequency cigarette dual users (5 minutes, OR: 2.85, 95% CI, 1.76–4.63; within 30 minutes, OR: 4.14, 95% CI, 2.96–5.80), and high-frequency dual users (5 minutes, OR: 4.46, 95% CI, 2.88–6.91; 30 minutes, OR: 3.94, 95% CI, 2.43–6.42). In addition, high-frequency e-cigarette dual users had significantly lower quit intention compared with both cigarette-only smokers and low-frequency dual users. Conclusions: Findings highlight the need for a standard, granulated classification of dual user, as important characteristics may vary between different categories. Future studies on dual use should consider categorizing dual use into the four classifications described in this study.