Electronic nicotine delivery system (ENDS) use has become more prevalent in the United States (U.S.) since its initial development (Cornelius et al., 2023). As the second most used tobacco product, 11.1 million Americans currently use ENDS, and the rate has increased since 2017 (Cornelius et al., 2023). Most adults who use ENDS do so to assist with combustible cigarette (CC) reduction or cessation (Adkison et al., 2013, Glasser et al., 2017, Rass et al., 2015). Yet, the utility of ENDS use in CC cessation (i.e., completely switching to ENDS) remains mixed (Bullen, 2014, Franck et al., 2014, Hajek et al., 2019, Kaisar et al., 2016, Kalkhoran and Glantz, 2016, Malas et al., 2016, Odum et al., 2012, Orellana-Barrios et al., 2016, Zborovskaya, 2017). Relative to completely switching to ENDS, dual use, defined as the concurrent use of CC and ENDS (Lee et al., 2018), is commonly observed among ENDS-using adults. In the U.S., 20.8% of individuals who smoke cigarettes daily engage in both CC and ENDS use (Assari & Sheikhattari, 2024). This is alarming given dual use is associated with greater nicotine exposure, more severe dependence, and greater number of cigarettes smoked per day (Bombard et al., 2007, Bombard et al., 2008, Soule et al., 2015, Wang et al., 2018). Further, individuals engaging in dual use (IEDU) are exposed to toxins and constituents, including carcinogens, at levels comparable to exclusive CC smokers (Shahab et al., 2017). Thus, health risks associated with dual use represent a central public health issue in need of clinical attention (Vindhyal et al., 2019).

The disease burden endured by IEDU is largely a consequence of maintained CC use given CC smoking at any rate increases one’s likelihood of disease and cancer (Berthiller et al., 2015, Garfinkel and Stellman, 1988). Yet, irrespective of CC use, ENDS use carries its own health risks, including inflammation, oxidative stress, and other deleterious effects on the lungs and airways (Chatterjee et al., 2019, Reinikovaite et al., 2018). The concurrent use of CC and ENDS may create a unique biologic environment for the onset and progression of illness and disease, particularly regarding cardiopulmonary health (Wang et al., 2018), and has been associated with increased risk of heart disease that is greater than the risk associated with either product used in isolation (Alzahrani et al., 2018, Osei et al., 2019). It is important to note, however, most (71.1%) IEDU desire to quit both products (Rostron et al., 2016). Previous studies have shown that individuals using CC experience success in ending CC use by switching to ENDS completely (Kasza et al., 2021). However, there is risk of continued use of both. Longitudinal work has found 89% of individuals who smoke CC who become dual ENDS users remain IEDU a year after initial assessment (Etter & Bullen, 2014) and more than one-fourth remain an IEDU two to three years after initial assessment (Osibogun et al., 2022, Osibogun et al., 2020). Additionally, discontinuation of CC and ENDS is rare, with only 7–11% of IEDU reporting comprehensive cessation (Coleman et al., 2019, Osibogun et al., 2022, Weaver et al., 2018). Despite a high level of interest in quitting both and low success in doing so, little work has examined factors related to the quit process among IEDU. This limitation in the current evidence is unfortunate given recent calls to focus on ENDS cessation (Sikka et al., 2021).

Clinically relevant factors associated with quit behavior among IEDU include individual differences in dependence, perceptions of quitting, and negative affective vulnerabilities, such as anxiety sensitivity (AS), emotional dysregulation, anxiety, and depression. Higher nicotine dependence has been identified as a robust predictor of unsuccessful quit attempts among individuals who use CC exclusively. (Cosci et al., 2011). By extension, increased nicotine or ENDS dependence may interfere with quitting both products among IEDU. For example, given that higher (Strong et al., 2017) or comparable (Sweet et al., 2019) levels of nicotine dependence is reported by IEDU relative to individuals who exclusively use CC, presumably due to notably high levels of nicotine (up to 60 mg/ml) found in more recent generations of ENDs (Kesimer, 2019), dependence may be a critical factor to examine in the context of quit behavior. Further, evidence indicates adult IEDU have more severe nicotine use and less success in their quit efforts than those exclusively engaging in CC or ENDS, including more years of using nicotine and more unsuccessful attempts to quit (Giovenco and Delnevo, 2018, Maglia et al., 2018, Peltier et al., 2020). As a result, IEDU may be more apt to report greater perceived barriers for quitting CC and ENDS and thus, they are more likely to have less quit success. Finally, negative affective states are known risk factors for quit difficulty across substances (Fatseas et al., 2018, Zale et al., 2016). IEDU often experience negative affect symptoms (Masaki et al., 2022), which, along with related vulnerability processes like AS and emotion dysregulation, contribute to worse cessation outcomes (Masaki et al., 2022). To date, however, no work has explored these factors within a framework to evaluate the nuanced approach to comprehensive cessation among IEDU.

The present study sought to understand differences in CC and ENDS dependence, perceived barriers for cessation across both products, and the constellation of negative affective vulnerabilities and states (i.e., AS, emotional dysregulation, anxiety, and depression) across (1) IEDU who never attempted to quit either product, (2) IEDU who reported an unsuccessful CC attempt in their lifetime, and (3) IEDU who reported an unsuccessful attempt to quit both products in their lifetime. It was hypothesized IEDU who reported an unsuccessful attempt in their lifetime to quit both CC and ENDS would report stronger CC and ENDS dependence and more perceived barriers for cessation for both products relative to the other two groups. Additionally, it was hypothesized IEDU who reported an unsuccessful attempt to quit both products would report elevated negative affective vulnerabilities as indicated by AS, emotional dysregulation, and depression and anxiety symptoms. Lastly, IEDU who attempted to quit CC only are hypothesized to report increased negative affective vulnerability symptoms compared to IEDU who never attempted to quit either product.