Objectives: Many smokers who start using ENDS engage in dual use of cigarettes and ENDS. This paper examines time trends in dual use after a JUUL Starter Kit purchase, and changes in cigarette consumption among those remaining dual users. Methods: In the ADJUSST study, a cohort of adult smokers who purchased a JUUL Starter Kit were followed naturalistically 6 times over 12 months. Trends in dual use and reported complete switching away from cigarettes (ie, no past 30-day smoking), and changes in daily average cigarettes per day from baseline at 6 and 12 months were examined. Results: Dual use declined over time as complete switching increased. By 12 months, 43.2% reported dual using, and 51.2% reported switching away from cigarettes. Among dual users, approximately 60% reduced their cigarette consumption substantially (by ≥ 50%); average reductions in cigarette consumption were > 80%. Only a small minority (3%-10%) substantially increased cigarette consumption. Conclusions: Dual use of smoking and JUUL declines over time as switching away from smoking increases. This suggests that, for most smokers, dual use is a transitional state leading to switching completely away from cigarettes. Furthermore, dual use is often marked by substantial reductions in cigarette consumption.