As of 2022, electronic nicotine delivery system (ENDS, including e-cigarettes or vapes) use was more prevalent than cigarette use from adolescence into the early 20s, and from the mid-20s to early 30s, prevalences were nearly identical (Bandi et al., 2021, Boakye et al., 2022, Erhabor et al., 2023, Meza et al., 2023). Since ENDS were introduced in 2007, both young adults with a history of smoking and those without have tried these products, some establishing habitual use and others using ENDS briefly (Bold et al., 2018, Harrell et al., 2021). Those who try ENDS for the first time do so for a variety of reasons including smoking cessation, advantages of ENDS over traditional cigarettes, the variety of flavors available, and curiosity (Romijnders et al., 2018). Despite a growing awareness of the reasons youth and young adults have for trying ENDS, little is known about whether these reasons are associated with ENDS use after initiation, or with continued use of cigarettes. If some reasons predict heavy or prolonged cigarette or ENDS use, they might be used to identify at-risk young adults. Cigarette and ENDS use are closely intertwined (Hiler et al., 2020, Leavens et al., 2019), yet research has also not examined how cigarette use prior to trying ENDS relates to reasons for trying ENDS. In the current study, we examined the interplay between cigarette use history, reasons for trying ENDS, and subsequent cigarette and ENDS use to explore the possibility that reasons for trying ENDS might indicate risk for future cigarette and ENDS use.

Among young adults who already use cigarettes, the most commonly-reported reason for initiating ENDS use is to quit or cut down on the use of cigarettes (Patel et al., 2016, Romijnders et al., 2018). Indeed, the marketing of ENDS emphasizes the benefits of switching from cigarettes to ENDS, with nearly 90 % of advertisements for ENDS comparing the devices to traditional cigarettes (Padon et al., 2017). However, the evidence as to whether adults who use ENDS are successful at quitting or cutting down their cigarette use is mixed. Recent clinical trials have compared assigning patients to use ENDS against various comparators (Eisenberg et al., 2020, Hajek et al., 2019, Walker et al., 2020), with each comparison finding some support for the utility of ENDS as a cigarette quitting tool under clinical supervision. Research with community samples, however, has largely found that adults who use ENDS are less likely to quit cigarettes, and may even use more nicotine after starting ENDS (Barrington-Trimis et al., 2018, Chaffee et al, 2018, Kosterman et al., 2021). A 2020 narrative review of correlational research from longitudinal cohort studies found that adults who used ENDS were not more likely to quit cigarettes, with adults who use ENDS frequently being less likely to quit than adults who do not use ENDS (Epstein et al., 2021, Hanewinkel and Isensee, 2015, Patil et al., 2020). This discrepancy in findings between clinical and community-based studies might be due to pre-existing differences in cigarette use for youth and young adults who try ENDS outside the context of a treatment study. Whereas randomization ensures that participants in a treatment study are matched on their pre-existing cigarette use, people who try ENDS on their own might already have more established patterns of cigarette use and desire to quit. More research on connections between prior smoking patterns and using ENDS to quit smoking is needed to understand the true consequences of using ENDS to quit.

Other commonly reported reasons for trying ENDS include the appeal and variety of available flavors and trying ENDS out of curiosity. Despite flavor regulations for certain types of ENDS, the majority of products come in many flavors, including fruit flavors (e.g., apple, mango) that differ greatly from the flavor of cigarettes (Lee et al., 2017). Existing young adult data suggest that when young adults try ENDS for the first time, they tend to use a flavored product (Harrell et al., 2017). Flavored ENDS are perceived as less harmful than non-flavored ENDS, in spite of a lack of research on the safety profile of flavored vs. non-flavored ENDS (Feirman et al., 2016). Some youth and adults also report trying ENDS out of curiosity (Pepper et al., 2014). What has remained relatively unexplored is how patterns of nicotine use, both before and after ENDS initiation, relate to reasons for trying ENDS.

Young adults with different smoking histories might have different reasons for trying ENDS; however, few prior studies have investigated differences in reasons by smoking status. We are aware of three studies (Patel et al., 2016, Pepper et al., 2014, Rutten et al., 2015) that have examined this question in cross-sectional online surveys, finding those who currently smoke cigarettes and those with a history of smoking to be more likely to report using ENDS to quit and out of curiosity than those who have never smoked. These three studies assessed prior smoking status at the same time as reasons for ENDS use and thus are reliant on retrospective self-report to determine smoking status. These studies also examined general adult samples, and do not present results for young adults. It is important to understand nicotine use in young adulthood, as patterns of use established at this time may persist into adulthood.

Reasons for trying ENDS may also predict future ENDS and cigarette use. Rutten et al. (2015) found that adults who reported using ENDS to quit cigarettes were more likely to report using ENDS recently. Saddleson et al. (2016) found that college students who were used ENDS daily were more likely to report using ENDS to quit than those who did not. These cross-sectional studies are unable to establish temporal ordering between reasons for ENDS use and later nicotine use. They may also be subject to confirmation bias and social desirability, in that people who use ENDS might be motivated to believe ENDS use contributed to quitting or reducing cigarette use. Longitudinal studies are needed to understand how motivations for ENDS use relate to subsequent cigarette and ENDS use to inform prevention programs.

The current study aimed to understand bidirectional links between reasons for trying ENDS and nicotine use by examining reasons relative to a) history of smoking prior to trying ENDS and b) use of cigarettes and ENDS 3 years after reasons were reported (see Fig. 1). In a large community longitudinal study of young adults that collected data at multiple waves throughout youth and young adulthood, we first examined links between smoking history and reasons for trying ENDS, hypothesizing that young adults who currently smoke would be most likely to try ENDS to quit cigarettes and to try a safer alternative, compared to young adults who never or infrequently smoke. Next, we examined whether reasons for trying ENDS were associated with subsequent cigarette and ENDS use measured 3 years later. We hypothesized that those who tried ENDS out of curiosity would be less likely to use ENDS 3 years later than those who did not. As evidence has been found for using ENDS to quit as both a risk and a protective factor for cigarette and ENDS use, we did not have a directional hypothesis related to quitting and later cigarette and ENDS use.