A Patchy Prohibition: Product and flavor substitution after the FDA's prioritized enforcement policy on flavored e-cigarettes.

This is the first detailed longitudinal study on e-cigarette sales trends in the US following the FDA flavor enforcement action, with novel findings on flavor trends and their relation to policy events. We report sales overall, by product type, and by flavor category, and highlight several important trends following the action, such as the rise and persistence of disposable e-cigarettes increasingly and overwhelmingly dominated by youth-friendly flavors, and likely substitution of prefilled e-cigarette flavor without any long-term decline in sales. Our results highlight the weaknesses of "patchy" regulation and suggest the need for a more comprehensive approach to flavor regulation.