US young adults have displayed decreases in cigarette use and increases in alternative tobacco product (ATP) use over the past decade, particularly for e-cigarettes (Cornelius, Wang, Jamal, Loretan, & Neff, 2020) compared to other ATPs (e.g., cigar products, hookah) (United States Department of Health and Human Services, 2021b). Those ages 18–24 more than doubled their past 30-day e-cigarette use from 2013 (12.5%) to 2019 (26.2%) (United States Department of Health and Human Services, 2021e) and report the highest rates of past-month e-cigarette use relative to other age groups (8.6% among adolescents (United States Department of Health and Human Services, 2021c), 6.6% among adults 25+) (United States Department of Health and Human Services, 2021d). Young adults also continue to report high rates of past-month cigarette use (18.1% in 2019) (United States Department of Health and Human Services, 2021a) and increasingly report dual use of cigarettes and e-cigarettes (e.g., 23% of e-cigarette users reported cigarette use in 2019 (Cornelius et al., 2020)).

Understanding changes in young adults’ cigarette and e-cigarette use is critical, as distinct use trajectories may have implications for cessation-related outcomes. While e-cigarette uptake may aid in cigarette cessation among some adult current smokers (McRobbie et al., 2014, Rahman et al., 2015) it may lead to increased risk of cigarette initiation among never smokers (McRobbie et al., 2014, Rahman et al., 2015), relapse back to smoking among former smokers (Soule, Plunk, Harrell, Hayes, & Edwards, 2020), and continued dual cigarette and e-cigarette use (Coleman et al., 2019, Grana et al., 2014). While dual use may reduce the burden of tobacco use if it influences subsequent reduction in cigarettes smoked or leads to quitting tobacco use entirely (Academies, 2018) it may pose significant health risks if sustained (Jorenby et al., 2017, Nayak et al., 2016).

Research has primarily examined trajectories of cigarette and e-cigarette use, separately. Young adults display trajectories of past 30-day cigarette use characterized by consistent low-level use, early high-level use followed by decreased use, consistent high-level use, and later-onset use (Berg et al., 2018, Bernat et al., 2008, Dutra et al., 2017, Hair et al., 2017, Riggs et al., 2007). Young adult e-cigarette use trajectories have included consistent low-level use, consistent high-level use, and later-onset use from adolescence through young adulthood (Harrell et al., 2021, Lanza et al., 2020, Park et al., 2020) based on past 30-day (Harrell et al., 2021, Lanza et al., 2020), or past 6-month (Park et al., 2020) use frequency. The limited research examining young adults’ dual cigarette and e-cigarette use has largely relied on correlational data examining associations among earlier cigarette use and later e-cigarette use or vice versa (Krishnan et al., 2022, Krishnan et al., 2022, Owusu et al., 2019). In one study examining use trajectories from 2015 to 2018, many adult cigarette users continued cigarette-only use or began dual cigarette/e-cigarette use; fewer reduced cigarette use and increased e-cigarette use (Owusu et al., 2019).

Understanding factors that differentiate trajectories of cigarette and e-cigarette use is imperative to inform tailored prevention messaging and cessation efforts. According to Social Cognitive Theory, individual-level factors (e.g., sociodemographics, psychosocial characteristics) predict tobacco use (Bandura, 1986). Research shows that men (versus women) are more likely to use cigarettes and report escalations in cigarette use (Berg et al., 2018, Hair et al., 2017, Higgins et al., 2015, Jamal et al., 2016), whereas sexual minority (versus heterosexual) young adults are more likely to use both cigarettes and e-cigarettes (Li et al., 2018;, Li et al., 2021, Romm et al., 2022). Some findings suggest that individuals identifying as White (vs Black, Asian, other race, or Hispanic) are at greater risk for cigarette (Nguyen-Grozavu et al., 2020, Romm et al., 2022) and e-cigarette use (Romm et al., 2022), whereas others suggest that individuals identifying as Black (vs White) are at greater risk for e-cigarette use and consistent patterns of cigarette use (vs decreases in use over time) (Hair et al., 2017, Keyes et al., 2015, Webb Hooper and Kolar, 2016). Moreover, younger age is associated with lowered risk for cigarette (Lydon-Staley and Geier, 2018, Romm et al., 2022), but greater risk for e-cigarette use (Cooper et al., 2016, Romm et al., 2022).

Key psychosocial factors related to young adult cigarette (Anda et al., 1999, Berg et al., 2013, Green et al., 2018, King et al., 2018, Martinasek et al., 2021, Mendel et al., 2012, Romm et al., 2022, Windle et al., 2018), and e-cigarette use (Green et al., 2018, King et al., 2018, Martinasek et al., 2021, Romm et al., 2022, Romm et al., 2022), are depressive symptoms and adverse childhood experiences (ACEs). Depressive symptoms are also associated with greater odds of adolescent dual cigarette and e-cigarette use (vs nonuse) (Audrain-McGovern, Rodriguez, Pianin, & Testa, 2021). Regarding personality traits, cigarette smokers versus nonsmokers report lower conscientiousness (e.g., goal-directedness and need for control) (Harakeh et al., 2006, Malouff et al., 2006, Terracciano and Costa, 2004) and agreeableness (e.g., hostility) (Harakeh et al., 2006, Malouff et al., 2006, Terracciano and Costa, 2004), and higher neuroticism (e.g., emotional instability) (Harakeh et al., 2006, Malouff et al., 2006, Terracciano and Costa, 2004, Zvolensky et al., 2015), extraversion (e.g., sociability) (Harakeh et al., 2006), and openness (e.g., creativity) (Zvolensky et al., 2015). Some similar findings have been observed for young adults’ use of e-cigarettes and dual use of cigarettes and e-cigarettes (Ozga-Hess, Felicione, Dino, Blank, & Turiano, 2020). In addition, other substance use, particularly alcohol and cannabis use (common among young adults (Schulenberg, Johnston, O'Malley, Bachman, & Miech, 2021)), is correlated with cigarette and e-cigarette use (Bluestein et al., 2019, Lozano et al., 2021, Schauer et al., 2015), and both are associated with greater likelihood of cigarette use continuation over time among young adults (Vogel, Rubinstein, Prochaska, & Ramo, 2018) and adults (Lynch, Twesten, Stern, & Augustson, 2019).

Much of this aforementioned research has been cross-sectional (King et al., 2018, Ozga-Hess et al., 2020, Terracciano and Costa, 2004, Windle et al., 2018), with less longitudinal research (Audrain-McGovern et al., 2021, Harakeh et al., 2006, Romm et al., 2022), and/or examined young adults’ cigarette or e-cigarette use status (i.e., current use vs non-use) (Lynch et al., 2019, Martinasek et al., 2021, Mendel et al., 2012, Vogel et al., 2018) rather than the nuances of the interplay of cigarette and e-cigarette use over time. The current study examined: 1) trajectories of young adults’ dual cigarette and e-cigarette use across 5 waves over a 2-year period; and 2) psychosocial predictors of these trajectories, including depressive symptoms, ACEs, and personality traits, accounting for Wave 1 (W1) sociodemographics and substance use.