Milestones in the natural course of the onset of e-cigarette dependence among adolescents and young adults: Retrospective study.

Introduction: There is considerable controversy about the development of dependence among e-cigarette users. This study describes the average amount of time using e-cigarettes before dependence milestones emerge and the differences in developing dependence between e-cigarette users who smoke cigarettes compared to those who do not.

Methods: Adolescents and young adults aged 16-25 living in Canada were recruited into an online survey in 2021. Current (past-month) e-cigarette users completed 15 items assessing dependence from the Penn-State Electronic Cigarette Dependence Index and the E-cigarette Dependence Scale for a total of 12 behavioural (e.g., difficulty refraining from vaping) and 3 frequency (e.g., using e-cigarette daily, weekly, or monthly) indicators of dependence milestones. Number of years after e-cigarette onset at which the cumulative probability of attaining each milestone was 25 % was computed.

Results: Among 1205 participants, most (80.6 %) were female, 73.7 % were Caucasian, and 49.7 % resided in Ontario. Ten of the 12 e-cigarette use milestones were attained by 25 % of respondents 2 years after starting vaping except for daily cigarette use (2.5 years after onset) and waking at night to vape (5.6 years after onset). Within the entire study population, frequency milestones (weekly, monthly, daily e-cigarette use) were attained faster by ever-smokers (hazard ratio compared to attainment by never-smokers: 1.12, 1.21, and 1.28 respectively), whereas for at least monthly users, behavioural milestones were attained faster by never-smokers.

Discussion: Many current e-cigarette users developed symptoms of e-cigarette dependence between two and five years since onset. Never smokers may be at higher risk of becoming e-cigarette dependent since they attained e-cigarette dependence milestones faster than smokers.