In 2022, more than 2.5 million (9.4%) middle and high school students reported current (past 30-day) use of e-cigarettes in the United States (US) (Park-Lee, 2022). Nicotine, the primary psychoactive substance in tobacco products, is harmful to the growing adolescent brain (Arrazola et al., 2015; Douglass et al., 2020; Kwan et al., 2020). Therefore, exposure to nicotine during adolescence and young adulthood, irrespective of the product, can increase the risk of nicotine dependence and future use of nicotine products (Vogel et al., 2019; Gaiha and Halpern-Felsher, 2020; Kwan et al., 2020). Factors such as higher nicotine concentration, increased vaping/smoking frequency, device type, and exposure to flavored e-cigarettes or cigarettes increase the risk for nicotine dependence (Azagba et al., 2019; Vogel et al., 2019; Kwan et al., 2020; Peterson et al., 2021; Tackett et al., 2021; Sargent et al., 2022). However, there is limited evidence on the time it takes for youth e-cigarette users to report symptoms of nicotine dependence, and little contemporary evidence of the same for youth cigarette smokers.

Most of our understanding of the time it takes to report symptoms of nicotine dependence among youth is based on studies on cigarette smoking from the late 1990s and early 2000s (DiFranza et al., 2000, DiFranza et al., 2007; Gervais et al., 2006; Dierker et al., 2008, Dierker et al., 2012; Zhan et al., 2012). However, since 2014, the prevalence of e-cigarette use has remained significantly higher among youth than the prevalence of cigarette smoking (Arrazola et al., 2015; Wang et al., 2020). About 1.6% (N = 440,000) of youth reported past 30-day (P30D) cigarette smoking in 2022, compared to 9.4% (N = 2.5 million) of youth who reported P30D e-cigarette use (Park-Lee, 2022). Consequently, research on nicotine dependence must account for changes in the preferred modality of tobacco use among youth.

Previous studies suggest that initiating cigarette smoking at a younger age is associated with an earlier transition to nicotine dependence, daily use, and significantly higher dependence severity than at an older age (DiFranza et al., 2000; Dierker et al., 2012; Huggett et al., 2018; Sharapova et al., 2020). For example, DiFranza et al. (2000) found that among younger adolescent ever-cigarette smokers aged 12–13 years, nearly a quarter reported their first symptoms of nicotine dependence within a month of transitioning to monthly use (i.e., smoking at least once per month) (DiFranza et al., 2000). In contrast, studies that included older adolescents indicated that the first signs of nicotine dependence occur within 1–5 years of cigarette smoking (Dierker et al., 2012; Zhan et al., 2012; Huggett et al., 2018). Among a cohort of teenagers who initiated cigarette smoking between the ages of 13–18, 25% of those who had smoked 100 or more cigarettes in their lifetime experienced at least one symptom of dependence within one year of ever smoking cigarettes (Zhan et al., 2012). Although heavier tobacco use correlates with a higher nicotine intake and increases the risk for dependence, the transition to dependence was much slower in those who started smoking at an older age (DiFranza et al., 2000; Zhan et al., 2012; Vogel et al., 2019; Hammond et al., 2021).

Additionally, nicotine dependence was previously thought to transition through phases, occurring after a regular tobacco use (e.g., daily use) pattern is established and a person has smoked at least 100 cigarettes in their lifetime (Evans et al., 1992; Lamkin and Houston, 1998). However, nicotine dependence can occur before adolescents' daily or weekly cigarette use is established (DiFranza et al., 2000; Gervais et al., 2006; Dierker et al., 2008). About 62% of adolescent ever cigarette smokers who transitioned to monthly cigarette smoking reported experiencing their first dependence symptoms before daily cigarette use occurred (DiFranza et al., 2000). Similarly, 20% of teenagers who had smoked <100 cigarettes in their lifetime reported dependence symptoms within a year of initiating use (Zhan et al., 2012). Moreover, 50% of adolescents who had only inhaled cigarettes at baseline reported dependence symptoms by the time they smoked seven cigarettes per month (DiFranza et al., 2007). These estimates highlight the complex interplay of biological and behavioral factors that lead to the development of nicotine dependence following exposure to nicotine (DiFranza et al., 2000; Dierker et al., 2012; Huggett et al., 2018; Sharapova et al., 2020).

To our knowledge, no study has examined the time to nicotine dependence among youth e-cigarette users in the US, nor is there a recent study on the time to nicotine dependence in adolescent cigarette smokers. We, therefore, sought to fill this knowledge gap in our study using nationally representative data from Waves 1–5 (2013–2019) of the Population Assessment of Tobacco (PATH) study. The objectives of this study are to 1) determine the time to signs of nicotine dependence among youth with exclusive P30D e-cigarette use 2) compare the time to signs of nicotine dependence for exclusive e-cigarette use to exclusive cigarette use to assess the abuse liability potential of e-cigarette use among youth. Abuse liability is defined as the probability that a product (e.g., tobacco) will be abused or cause dependence (Carter et al., 2009). We hypothesize that the time to the signs of nicotine dependence will be shorter for youth with exclusive cigarette use than for those with exclusive e-cigarette use.