PURPOSE: E-cigarette use among adolescents and young adults (AYAs) remains prevalent in the United States and is linked with combustible tobacco product use. This study examines sociodemographic differences (i.e., sex, age, sexual identity, transgender identity, race, ethnicity, and income) in transitions from e-cigarette use to other forms of tobacco use among AYAs from 2014 to 2023. METHODS: AYAs aged 14-25 years from the nationally representative Population Assessment of Tobacco and Health study waves 2-7 (2014/15-2022/23) were used to examine transitions in e-cigarette and combustible tobacco use over 1-to-2-year periods (n = 7,523). Using multinomial logistic regression models, we examined associations of sociodemographic characteristics and wave with e-cigarette and combustible tobacco transitions. RESULTS: Maintaining e-cigarette use only (21.2% in 2014/15-49.2% in 2022/23) and transitioning from e-cigarette and combustible use (i.e., dual use) to e-cigarettes only (7.6% in 2014/15-29.7% in 2022/23) increased over time. Simultaneously, transitioning from e-cigarettes to dual use (18.2% in 2014/15-17.9% in 2022/23) and maintaining dual use remained steady. Bisexual individuals were more likely to transition from e-cigarette use only to dual use (adjusted relative risk ratio = 2.07
95% confidence interval = 1.44, 2.99) and maintain dual use (adjusted relative risk ratio = 2.01
95% confidence interval = 1.43, 2.84), compared to heterosexual individuals. Female, Hispanic, and Black individuals were less likely to transition to dual use or maintain dual use compared to male, non-Hispanic, and White individuals, respectively. DISCUSSION: Findings identify important sociodemographic groups at greater risk of transitions to combustible tobacco use that warrant attention in future research and prevention strategies to reduce health disparities.