1. Introduction

The weight of current scientific evidence about electronic nicotine delivery systems (ENDS) suggests that these products can be a substantially less harmful, though not harmless, alternative source of nicotine for cigarette smokers with potential for population harm reduction under the right conditions (McNeill et al., 2018; National Academies of Sciences, Engineering, and Medicine, 2018; Royal College of Physicians, 2016). For ENDS to achieve population health improvement, smokers who would not have otherwise quit smoking would need to completely substitute their smoking with ENDS, optimally in transition to complete tobacco and nicotine abstinence, at levels that counter any concomitant increases in youth and young adult nicotine and tobacco use caused by ENDS (Levy et al., 2017; Warner and Mendez, 2018). Most smokers who use ENDS report using them to quit or reduce smoking, and a recent randomized trial found that a second-generation ENDS was more efficacious than nicotine replacement therapy under advantageous circumstances where trial participants were provided a newer generation ENDS, cessation counseling, and instruction and guidance on using the provided ENDS (Hajek et al., 2019; Simonavicius et al., 2017; Yong et al., 2019). Studies of U.S. smokers’ use of ENDS under real-world conditions have generated inconsistent findings regarding their effectiveness for quitting smoking (Giovenco and Delnevo, 2018; Halpern et al., 2018; Levy et al., 2018; Rigotti et al., 2018; Sweet et al., 2019; Weaver et al., 2018; Zhu et al., 2017).

While much focus has been on the dual use of cigarettes and ENDS, the smokers who have tried or used but discontinued ENDS while continuing to smoke has been referred to as “a missed opportunity for harm reduction” (Simonavicius et al., 2017). Although fewer in number compared to dual users, approximately one-quarter of US adult smokers in 2015 had tried or used but discontinued ENDS while continuing to smoke (Weaver et al., 2017). In recent longitudinal research, more than one-third of dual users at baseline had discontinued using ENDS while continuing to smoke within one year and more than one-half had done so within two years (Kasza et al., 2018; Manzoli et al., 2017; Weaver et al., 2018). In a 2016 survey of British smokers, the most common reasons given for discontinuing ENDS were that they did not sufficiently mimic the feel of smoking or reduce cravings to smoke (Simonavicius et al., 2017). Two US surveys conducted in 2013–2014 found that one-third of smokers who discontinued ENDS indicated they were too expensive or did not feel “like smoking cigarettes”, while substantial proportions also referred to their taste, concerns about health risks, and malfunction or poor function as reasons (Biener et al., 2015; Biener and Hargraves, 2015). A more recent, multi-country study that included U.S. participants reported the top reasons given by smokers for discontinuing ENDS centered around dissatisfaction with ENDS, particularly with relieving cravings to smoke or helping them quit smoking (Yong et al., 2019). Since these studies were conducted, the ENDS market and regulatory landscapes have continued to evolve (Huang et al., 2019a; Rigotti, 2018). These changes, as well as the intense public scrutiny of ENDS in the U.S., over the past couple years could have led to shifts in reasons for non-use.

Smokers who want to quit smoking but have not tried ENDS also warrant examination. Most smokers express regret having ever started smoking and want to quit, but nearly 40% of smokers have not tried ENDS despite their marketing and promotion as an alternative to smoking (Pechacek et al., 2017; Weaver et al., 2017). To the extent that ENDS can be effective for achieving complete smoking abstinence, factors that reduce their appeal to and inhibit their uptake by a substantial segment of adult smokers could limit their population harm reduction potential. One possible explanation is the growing perception among smokers that using ENDS is equally or more harmful than smoking cigarettes (Huang et al., 2019b; Majeed et al., 2017; Nyman et al., 2019). In the UK, which has observed lower prevalence but similar trends in this perception, the modal reason given by smokers for not trying ENDS in 2016 was concerns about their safety (27%), followed closely by not wanting to substitute one addiction for another (25%) and doubts about their effectiveness for quitting or cutting down their smoking (22%) (Action on Smoking and Health, 2016; Wilson et al., 2019).

Continued monitoring is needed of smokers’ reasons for the disuse of ENDS, which may be changing as a result of market evolution and the intense and highly public, polarized discussions around ENDS. Understanding the smoking and ENDS use characteristics, perceptions, and intentions to use ENDS in the future of smokers who have tried or used but discontinued ENDS or who have chosen not to use ENDS while continuing to smoke and their reasons for doing so could inform efforts to achieve their harm reduction potential. For instance, targeted education campaigns could inform smokers who cite concerns about the safety of ENDS as their reason for not trying or for discontinuing ENDS use and perceive them to be as harmful as or more harmful than smoking cigarettes about the current evidence on the relative harm of ENDS relative to cigarettes. And data about these smokers’ openness and intentions for future use of ENDS provide useful information about the extent to which their decision to not use ENDS could be malleable to external factors. Accordingly, the objectives of this study are to examine: (a) smoking and ENDS use characteristics, perceptions (such as perceived harm and, for former users, perceived enjoyment), and future use intentions among those smokers who have either not tried or discontinued using ENDS; (b) the reasons a segment of smokers give for discontinuing ENDS, overall and by extent of their prior ENDS use (experimental vs. regular), type of ENDS, and flavor; and (c) the reasons given by smokers for not trying ENDS, overall and by smoking quit intentions, age, and perceived harm of ENDS.

2. Methods

3. Results

4. Discussion

The findings of this study provide important, more recent insights into the reasons U.S. smokers give for their discontinuance or never use of ENDS and have implications for policies and regulations aimed at optimizing their potential for harm reduction. In this study, more than 70% of current smokers had either never used or discontinued using ENDS while continuing to smoke. While the question whether these smokers represent a missed opportunity for harm reduction depends on whether ENDS are effective for quitting, the reasons these smokers provided may indicate why previous studies have not found ENDS to be effective for quitting under real-world use conditions (Halpern et al., 2018; Rigotti et al., 2018; Sweet et al., 2019; Weaver et al., 2018).

Not satisfactorily replicating the “feel” of smoking or reducing their cravings to smoke were the primary reasons that 37% of current smokers who formerly used ENDS gave for discontinuing them, particularly by smokers who had used rechargeable, non-refillable system ENDS. Indeed, more than 75% of these smokers reported that using ENDS was less enjoyable than smoking cigarettes. These reasons were also commonly reported by UK smokers, a multinational sample that included some US smokers, and earlier studies of US smokers and are consistent with research indicating that ENDS generally have not delivered nicotine comparably to cigarettes (Action on Smoking and Health, 2016; Biener et al., 2015; Farsalinos et al., 2018; Hajek et al., 2017; Yong et al., 2019). In contrast to two earlier US-based studies (Biener et al., 2015; Biener and Hargraves, 2015), the current study did not find cost or malfunction to be dominant reasons. Although curiosity was also a prevalent reason, it was mostly endorsed by smokers who only used ENDS experimentally – most of these former ENDS users – or smokers who had used non-rechargeable ENDS (the least used device type). A UK survey also reported curiosity has the second most endorsed reason for no longer using ENDS (Action on Smoking and Health, 2016). Non-rechargeable (disposable) ENDS typically have a cigarette-like appearance, are generally sold where smokers would purchase cigarettes, and have lower upfront costs than rechargeable e-cigarettes, which might make them more attractive to smokers who are merely curious to try them (Braak et al., 2019; Grana et al., 2014; Liber et al., 2017; Sussman and Barker, 2017). Smokers who had used ENDS regularly, on the other hand, were more likely than experimental former users to endorse that they were using them too often as reasons for their discontinuation. Disposable and rechargeable, closed-system ENDS are likely to be easier to use, but they were less likely to provide comparable delivery of nicotine relative to rechargeable, refillable systems (Farsalinos et al., 2018; Hajek et al., 2017). Smokers who had used these ENDS regularly may have had to use them more frequently than they had to smoke cigarettes in order to satisfy their cravings. However, this is likely to change with the rising use of JUUL and other similar ENDS that use nicotine-salts and higher nicotine concentrations that deliver nicotine comparable to the refillable ENDS and cigarettes such that smokers may no longer need to use these newer ENDS more frequently to satisfy their cravings (Goniewicz et al., 2018; Huang et al., 2019a; Talih et al., 2019). These former regular ENDS users may also have been using ENDS in situations in which they could not smoke cigarettes. To a lesser extent, though at levels twice that of UK smokers, concerns about their safety were also reported (Simonavicius et al., 2017). Less than 40% of former regular ENDS users and less than 30% of former experimental ENDS users believed ENDS were less harmful than smoking cigarettes. The difference with UK smokers may stem from more prevalent perceptions in the US that ENDS are equally or more harmful than cigarettes and differences in media coverage and messaging from public health and medical organizations in the two countries (Huang et al., 2019b; Wackowski et al., 2019; Wilson et al., 2019). That 33% of former users who had used regularly would probably or definitely try ENDS soon (51% would probably or definitely try if offered by a best friend) indicates that this group has not completely rejected ENDS and is open to future use. Former experimental users were less open to trying ENDS in the future (14% said they would probably or definitely try soon), though at least one-third would probably or definitely try them if offered by a friend.

Whereas current smokers who had formerly used ENDS largely cited reasons of inadequate craving reduction or incomparability to smoking for their discontinuation, the larger segment of current smokers who have never used ENDS cited different reasons for non-use, namely concerns about substituting one addictive product for another, perceived ineffectiveness for quitting smoking, and concerns about their safety. Indeed, these smokers were less likely to perceive ENDS as less harmful than smoking and more likely to be uncertain about the relative harms than former, regular ENDS users. In addition, most of these smokers perceived nicotine as definitely harmful to adults, which might explain their reluctance to substitute one addictive product (ENDS) for another (cigarettes) and concerns about the safety of ENDS. That smokers with stronger quit intentions were also more likely to cite as a reason that they were using other methods for quitting smoking might suggest that they perceived ENDS to be less effective and/or less safe relative to other quit approaches and may have a stronger motivation to cease their nicotine addiction. While these smokers have no direct experience using ENDS, their perceptions of their safety (or lack of) could be explained by the media coverage and public health messaging on ENDS (Wackowski et al., 2018, 2015). Similarly, the medical and public health organizations have been cautious, if not resistant, to endorse ENDS for smoking cessation as the US-based research on their effectiveness has been mixed, if not generally negative; and this too has received extensive media coverage (Bhatnagar et al., 2019; Douglas et al., 2018; National Academies of Sciences, Engineering, and Medicine, 2018). Concerns about substituting one addiction for another was the most commonly endorsed reason for not trying ENDS. Perhaps for these smokers, particularly those with greater quit intentions, the best approach may be to help them quit rather than encourage them to switch to ENDS. The perceived financial cost of ENDS was also cited as a reason for not using them. While the long-term costs of ENDS are generally lower than smoking, their initial costs are often greater (Cantrell et al., 2018; Wang et al., 2018). Taxation and other policies that increase the cost to purchase ENDS may deter their use among smokers who have not yet used them (Huang et al., 2018).

Role of funding source

This work was supported by the U.S. National Institute on Drug Abuse, National Institutes of Health (NIH) and the Food and Drug Administration (FDA) Center for Tobacco Products (CTP) (grant number P50DA036128). The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH or the Food and Drug Administration. The funding agencies had no involvement in the study design; collection, analysis and interpretation of the data; writing of this report; or in the decision to submit the article for publication.

Contributors

All authors contributed to the design of the study and interpretation of the data. SW developed the analysis plan, and JH performed the data analysis. SW wrote the first draft and all authors contributed to revision of the paper and approve the submitted version.