The analyses presented here assessed the predictors of self-reported past-30-day abstinence from smoking in 3 consecutive surveys at months 6, 9, and 12. in a sample of adult smokers who purchased a JSK. In the evaluable sample, 21.6% reported such repeated point prevalence switching away from smoking. While considerably lower than the single point-prevalence switching rates of 47% – 51% at those months, this is a substantial proportion of these smokers, particularly considering that half them were not ready to quit smoking when they first purchased a JSK (Table 1). Also, even among those not ready to quit at baseline, 18% reported RPPS over the last 6 months of the following year. The data also indicate that over three-quarters of those who achieved RPPS during months 6 to 12 had already switched away from smoking at month 3, suggesting that switching was often more prolonged than was captured by the RPPS end-point used here.
As expected, individuals with a lighter smoking history (lower baseline smoking frequency, quantity, duration, and dependence) were more likely to achieve RPPS, consistent with predictors of clinical smoking cessation.[38–42] Studies on switching with ENDS also showed similar results: lighter and less dependent smokers at baseline were more likely to report complete cigarette abstinence and reduced their cigarette consumption more greatly. As heavier smokers may take longer to achieve complete switching, further follow-up beyond the initial first year would be informative.
Interestingly, the strongest predictors of subsequent RPPS reflected how participants were using and reacting to JUUL. Those who at 3 months were using JUUL daily and using it more times per day, who scored higher on JUUL dependence, and who reported greater reinforcing effects from using JUUL were more likely to subsequently achieve RPPS. Similarly, even among those who were already switched at month 6, daily use of JUUL and greater perceived reinforcing effects increased the odds of maintaining the switched status at months 9 and 12. These findings are consistent with prior studies that have similarly reported that daily ENDS use is associated with switching.[15–20, 44] Previous research has shown that switchers (i.e., former smokers who are currently using ENDS) report that the subjective sensations from ENDS were important in their transition from cigarette smoking to exclusive ENDS use. Indeed, users’ subjective responses on ENDS, such as reduction in cigarette craving and ENDS liking, were associated with higher odds of switching and greater smoking reduction.[24, 45] The present finding extends that association to RPPS, consistent with the hypothesized role of ENDS to displace cigarette smoking.[46, 47]
Collectively, the present findings suggest the role of ENDS/JUUL use, and its potential to substitute for cigarettes, as an important factor in switching away from smoking. This is consistent with the conceptualization of ENDS as substitutes for cigarettes, and with Abrams et al.’s conceptual model, which emphasizes that ENDS need to provide satisfaction sufficient to promote and reinforce use in order to compete with cigarettes and facilitate switching (see also Gray et al.). The importance of ‘abuse liability’ of ENDS in facilitating smokers’ switching has been similarly recognized by the Food and Drug Administration’s Center for Tobacco Products.
It was notable that among the participants who did not achieve RPPS, but who had switched at one or more follow-ups at 6, 9, and 12 months, reported much-reduced cigarette consumption, with over 80% reporting reductions of at least 50%. Some of these participants may have been getting close to achieving abstinence at all three time points. The substantial reductions in cigarette consumption observed in those who did not achieve RPPS are consistent with Selya et al.’s report that most ADJUSST participants who were engaged in dual-use had reduced their cigarette consumption by at least 50%, a degree of reduction that has been associated with very substantial reductions in exposures to smoking-related toxicants,[8, 10] and has been associated with reductions in disease risk, particularly for cancer.[7, 9, 10]
Although cigarette- and JUUL-related variables were the strongest predictors of RPPS, two demographic factors also emerged as predictors in adjusted models. Married smokers were more likely to achieve RPPS. This association has also been observed in smoking cessation, and likely reflects the availability of social support and other psychosocial resources. Consistent with Kim et al.’s observations from ADJUSST, non-Hispanic Asian smokers were slightly less likely to achieve RPPS, even after controlling for other variables. It is not clear why this is so, and this is a topic worthy of further research.
This study has several limitations that should be taken into account. The ADJUSST study had no control group or randomization, precluding strong causal inferences. Nevertheless, the consistent associations of greater JUUL use and JUUL reinforcement with RPPS suggest that JUUL use may play a role in RPPS. The scope of this study was limited to cigarette smoking and JUUL use behaviors, and it did not capture the use of noncigarette tobacco products (i.e., cigar, cigarillo, hookah, etc.) at baseline or follow-up.
RPPS was defined based on self-report, without biochemical verification, consistent with other observational studies on switching.[13–17] As in many longitudinal surveys, some participants did not complete all follow-up surveys, resulting in missing data. In some cases, missing data made it impossible to establish participants’ RPPS status over all three follow-ups. While there is a possibility of selective drop-out (i.e., those who switched continued responding while those who returned to smoking stopped responding to the survey), analyses of survey response in ADJUSST suggests that the potential for bias from differential response rates was limited. Nevertheless, it remains a limitation.
While a similar definition has been used to assess multi-year sustained switching with PATH data by Kalkhoran and colleagues, RPPS does not necessarily imply continuous abstinence over the 6-month period. Conversely, even the reports of smoking at a follow-up do not necessarily imply a full return to smoking, as even reporting one puff of smoking in the month preceding any of the three assessments assigned the participants in the ‘non-RPPS’ group. A dynamic analysis of more detailed trajectories might provide useful additional insight.
Participants were recruited based on their purchase of JSK, so may not necessarily represent the general population of cigarette smokers or even all ENDS users, which are often defined on the basis of any use in the past 30 days, and thus including experimental triers. Purchase of a JSK likely indicates a degree of commitment to JUUL use, and this may help explain higher rates of complete switching at 12 months, compared to other studies.[13–17] The study also followed smokers from their first JSK purchase, so may better capture trajectories over time. Many longitudinal studies start with many ENDS users who are dual users at baseline and therefore may omit smokers who already have successfully switched and overrepresent those unable to switch.
This study focused on users of JUUL, a particular pod-based nicotine-salt ENDS product, and it is not clear how results might apply to other ENDS, which are highly heterogeneous in nicotine delivery and other factors. Some studies have reported that JUUL can deliver nicotine in a manner similar to cigarettes,[50, 51] which has been suggested as an important feature of ENDS that facilitates smokers to switch.[46, 50, 51] Thus, the generalizability of the findings to the range of other ENDS products is unknown.
The study also had multiple strengths. This study extended follow-up analyses from a single time-point to RPPS over a six-month period. We analyzed a large sample of baseline smokers who had just purchased JUUL, addressing the limitations of some previous studies, including small sample sizes. The participants represent real-world adopters of ENDS, and were followed forward from their initial purchase, making the results of this study more readily interpretable in terms of smokers’ trajectories, and perhaps more applicable to real-world use. The analyses included details of smoking history and JUUL use patterns that enabled informative predictive models.