Health Risks Associated with Adopting New-Generation Disposable Products Among Young Adults Who Use E-Cigarettes.

New-generation disposable e-cigarettes have become increasingly popular among young adults in the USA since the FDA's partial flavor ban. This study aims to examine longitudinal changes in health risks among young adults who adopted these novel products, as well as the health effects of device types beyond the effects of other important e-cigarette characteristics. This study recruited e-cigarette users via voluntary response sampling from three college campuses in the USA to respond to four-wave online surveys conducted in four consecutive semesters. Among the participants who adopted disposables during the study, their health risks (dependence symptoms, respiratory symptoms, combustible tobacco use) and e-cigarette consumption characteristics (use frequency, nicotine concentration and flavors) before and after the adoption were compared using paired-sample t- or McNemar's tests. Generalized linear mixed models with a random intercept were conducted on data from the entire sample to investigate the effects of device type (tank, cartridge/pod, disposable) on health risks, controlling for other e-cigarette consumption characteristics. The study sample of 650 e-cigarette users were, on average, 20 years old, with 49% being male, 70% being White, and 13% being Hispanic. Adopting disposables may increase secondary dependence motives (t = 2.42, < 0.05) and the use of higher levels of nicotine concentration (t = 2.09, < 0.05) and sweet flavors (x = 22.53, < 0.05) but decrease the number of times of vaping per day (t = -2.18, < 0.05) and the use of menthol flavors (x = 4.57, < 0.05). Tank use is associated with a higher level of primary dependence motives (b = 0.1998, < 0.05) and a greater odds of using combustible tobacco (b = 0.4772, < 0.05). Although disposable use is not associated with the likelihood of using combustible tobacco, it is associated with higher levels of both primary (b = 0.2158, < 0.05) and secondary (b = 0.2533, < 0.05) dependence motives. It is not the device type, but rather the frequency of vaping, that affects respiratory symptoms (b = 0.0602, < 0.05). The findings indicate that when young adults switch to disposables, their e-cigarette dependence and use of sweet-flavored e-liquids increase. Even after controlling for use frequency, nicotine concentration and flavors, using disposables is related to not only instrumental motives that are influenced by psychological and environmental contexts but also heavy, automatic use that can operate without environmental cues. Given the health risks associated with disposable e-cigarettes, more comprehensive tobacco product regulations that consider the impact of device types may be needed.