To our knowledge, no studies have compared indicators of prior or current dependence on smoking, or likelihood of relapse, among former smokers who vape versus those who do not vape. Data for this study come from the 2016 International Tobacco Control Four Country Smoking and Vaping Wave 1 Survey (4CV1). We used indicators of cigarette smoking dependence shown to be predictive of smoking cessation (time to first cigarette, usual daily cigarette consumption and perceived addiction to smoking) 26 - 28 , or relapse (self‐efficacy in remaining quit and urges to smoke) 29 , 30 . The sample was limited to former smokers (i.e., ever daily smokers) who had quit in the previous 2 years. The research questions addressed: (1) do recent former smokers who currently vape nicotine daily (vapers) differ from former smokers who do not currently vape (non‐vapers) in time to first cigarette and usual cigarette consumption when they were smoking reported retrospectively; and (2) do vapers differ from non‐vapers, when surveyed, on perceived addiction to smoking, urges to smoke and confidence in their ability to stay quit?

In a recent trial involving smokers attending specialist behavioural support cessation services 15 , smokers were randomized to use either NVP or NRT. Those using NVP were approximately twice as likely to remain cigarette‐abstinent than NRT. It was also found that the percentage of participants who continued their NVP use was greater than the rate of continued NRT use. This pattern of findings points to the importance of continued NVP use in ameliorating withdrawal symptoms, and possibly in maintaining positive effects previously obtained from smoking. These findings are consistent with other studies that have examined the relation between cigarette smoking craving/dependence and vaping. For example, greater reductions in craving to smoke have been found among vapers than NRT users 16 , 17 despite, in the latter study, roughly similar nicotine intake to cigarette smoking among both groups 18 . The psychoactive effects of some NVPs 19 may also sustain NVP use after switching. Several studies have examined dependence on vaping versus prior dependence on smoking 9 , 20 - 23 , or dependence in vapers compared with similar samples of smokers 24 , 25 , consistently finding lower vaping dependence.

It has been proposed that many smokers switch to vaping because their addiction to nicotine makes this their only viable route out of smoking. Former smokers who vape report retrospectively that they had smoked for a longer duration and had higher consumption and dependence compared with a similar sample of smokers 8 . Vaping appears to address both nicotine withdrawal and some of the learned behavioural aspects of smoking that make giving up cigarettes difficult for smokers. For example, studies have found that satisfaction or enjoyment from vaping were associated with not smoking and continued vaping or intentions to continue vaping 9 - 11 . In addition, qualitative research studies report that NVPs provide a substitute for many of the physical, behavioural and social aspects previously enjoyed from smoking 12 , 13 , and that vaping might interrupt the known pathway between lapse and relapse 14 .

Given the enormous health risks posed by cigarette smoking, it seems clear that switching completely to non‐combustible nicotine products will reduce health risks compared with continued smoking 1 - 3 . In many countries, nicotine vaping has become a popular method used by smokers to stop smoking cigarettes 4 , 5 . In other words, vaping has meant that some smokers are stopping smoking by switching completely to nicotine vaping products (NVP), similar to how some smokers stop by switching to nicotine replacement therapies (NRT), such as gum or lozenge 6 , 7 .

In relation to objective (1) based on prior literature, we would expect that vapers would be more likely to have been more dependent smokers prior to quitting, i.e., smoked within 5 minutes of waking and had higher cigarette consumption when smoking. In relation to objective (2) based on prior literature, we would expect vapers to have fewer urges to smoke. Given the lack of prior literature we were unsure whether vapers and non‐vapers would differ in relation to perceived addiction to smoking and confidence in ability to stay quit at the time of the survey. In relation to covariates, we predicted that former smokers who had been quit for a longer time would have reported lower retrospective measures of smoking dependence, lower perceived addiction to smoking and urges to smoke and higher confidence in ability to stay quit.

We estimated weighted logistic regression models using SUDAAN version 11.0.1 to examine the association between vaping status, and each of the two retrospective, and three current, predictors controlling for all covariates listed above. We carried out a sensitivity analysis by removing the AU CCV sample. Don't know/refused responses were coded as missing. All cases with missing data were excluded from the analysis, using casewise deletion. There were 36 missing cases for TTFC analysis, five for cigarette consumption analysis, 44 for perceived addiction analysis, two for urges to smoke analysis, and one for confidence in remaining quit analysis. There were nine missing cases for ethnicity, 11 for education and no missing data on the other covariates.

The measure used was based on the Strength of Urges to Smoke Scale, found by Fidler and colleagues 35 to be the strongest predictor from a number of dependence measures included at baseline, of success of subsequent quit attempts. We combined their two questions into one, with six possible responses. Thus, for all former smokers, urges to smoke were assessed: ‘In general, how strong have urges to smoke been in the last 24 hours: I have not felt the urge to smoke in the last 24 hours, slight, moderate, strong, very strong, extremely strong, refused, don't know’? We modelled the odds of having any urges (slight/moderate/strong/very/extremely strong to smoke) versus no urges, given the preponderance of reporting no urges to smoke in the last 24 hours, with don't know/refused excluded.

This measure is from the Cigarette Dependence Scales 5 and 12 27 , and the only one from these Scales in a recent study to predict smoking cessation in addition to HSI 34 . The measure used here was adapted to be in line with other ITC questions and asked of all former smokers: ‘Do you consider yourself addicted to cigarettes: not at all, yes—somewhat addicted, yes—very addicted, refused, don't know’? We modelled the odds of being ‘very addicted’ versus otherwise, with don't know/refused coded as missing and excluded.

This measure is taken from the FTCD 32 and together with TTFC forms the HSI, which accounts for much of the predictive validity of the FTCD 33 . All former smokers were asked: ‘Now thinking about the months before you quit smoking [and were not vaping regularly], on average, how many cigarettes did you smoke?’. Respondents could answer with cigarettes/day or cigarettes/week and cigarettes/day was derived for all, which was then classified into two categories, ≤ 10 cigarettes/day and > 10 cigarettes/day (given that usual daily cigarette consumption among smokers in 2016 in England averaged 11 cigarettes).

This measure is taken from the Fagerstrom Test for Cigarette Dependence (FTCD 32 ) and Heaviness of Smoking Index (HSI 33 ), and it has been shown to have the greatest validity of the FTCD and HSI measures for smoking cessation and relapse 26 . All former smokers were asked: ‘Thinking about when you used to smoke, how soon after waking did you usually smoke your first cigarette?’, with the response completed in minutes or hours as appropriate. The distribution of time to first cigarette data were skewed, and for the analysis these were classified as a binary outcome; we modelled odds of first cigarette within 5 minutes versus more than 5 minutes.

Vaping nicotine was assessed using the question: ‘What is the strength of the e‐liquid you currently use most? No nicotine, 0 mg/ml; 1–4 mg/ml (0.1–0.4%); 5–8 mg/ml (0.5–0.8%); 9–14 mg/ml (0.9–1.4%); 15–20 mg/ml (1.5–2.0%); 21–24 mg/ml (2.1–2.4%); 25 mg/ml (2.5%) or more); refused; don't know’. For those responding ‘refused’ or ‘don't know’, they were asked: ‘Can you tell us the rated strength of the e‐liquid you [use most]/[last used] (often written on the package or cartridges)? No nicotine; low/light; medium/regular’. All those responding ‘no nicotine’ or ‘refused/don't know’, followed by ‘no nicotine’, were excluded. Thus, the two analytical samples were former smokers who were ever daily smokers, who currently vaped nicotine daily (vapers) or who currently did not vape (non‐vapers).

In this study, we were interested in examining whether former smokers who were substituting their nicotine from combustible cigarettes through regular daily vaping differed from those who were not vaping. As a result, we excluded from our analyses current vapers who did not vape daily or who vaped a non‐nicotine containing product. Current daily vapers were identified according to whether those that responded ‘daily’ to the following question: ‘How often, if at all, do you currently use e‐cigarettes/vaping devices (i.e., vape)? Current non‐vapers were identified as those who responded ‘not at all’, and they were also asked if they had ever vaped and if so, how frequently.

Data are from the ITC 4CV1 Survey collected in 2016 from four countries: Australia (AU), Canada (CA), England (EN) and the United States (US). Methodological details are available via the ITC website ( http://www.itcproject.org/methods ) and in Thompson et al . 31 . In brief, the 4CV1 sample retained participants from the original ITC 4C Survey (conducted 2002–15) who met eligibility criteria and recruited new participants who were current smokers or vapers or who had quit smoking within the last 2 years from country‐specific panels. In CA, EN and US there was oversampling of those aged 18–24 years and/or those with experience of vaping, but this was performed in a way that allowed us to weight the samples back to reference representative surveys. In addition, a supplementary dedicated vaper sample was recruited in AU from on‐line vaper forums and vape stores [Australian Cancer Council Victoria (CCV) sample]. We included this sample in our analyses in order to have a large enough sample of former smokers overall, and particularly from AU, where NVPs are effectively banned from retail sale. The data were weighted to be representative of former smokers in CA, US and EN irrespective of whether or not they vaped; for AU, non‐vapers had an initial weight to make them representative of AU former smokers, but vapers were given a weight to make them representative of current vapers in AU (irrespective of whether or not respondents were from the CCV sample).

Vapers were significantly more likely to report feeling extremely confident in their ability to stay quit (62.1%, 95% CI = 52.5%, 70.9%, n = 317) compared with non‐vapers (36.6%, 95% CI = 1.6%, 41.9%, n = 240) (Wald F = 17.43, P < 0.001) (Supporting information, Table S2 ). This relationship remained significant after controlling for other measures (aOR = 3.22, 95% CI = 1.86, 5.59, χ 2 = 17.36, P < 0.001) (Table 2 ). Additionally, among all former smokers, those who had quit less than 1 year ago were significantly less likely to feel extremely confident than those quitting 1–2 years ago; and those of moderate education were more likely to feel extremely confident than those of high education. Those in the Australian vaper sample were more likely to feel confident in staying quit than respondents from the other sample sources.

By contrast, 27.7% (95% CI = 18.9%, 38.7%, n = 68) of vapers reported experiencing any urges to smoke in the last 24 hours at the time of the survey, compared with 38.8% (95% CI = 37.7%, 44.3%, n = 244) of non‐vapers (Wald F = 3.87, P = 0.049) (Supporting information, Table S2 ). This relationship was no longer significant in the multivariable analysis (aOR = 0.86, 95% CI = 0.44, 1.65, χ 2 = 0.21, P = 0.643) (Table 2 ). Additionally, among all former smokers, time since quitting was a significant predictor, with those quitting in the last 12 months being significantly more likely than those quitting 1–2 years ago to report experiencing any urges to smoke, as were white former smokers compared to non‐white former smokers, and those aged 55+ years compared to 25–39‐year‐olds. Similarly, those in AU versus those in the US and EN, and those from other sources compared with the AU CCV, were significantly more likely to report experiencing any urges to quit in the last 24 hours.

Among vapers, 41.3% (95% CI = 31.4%, 52.0%, n = 174) perceived themselves to be still very addicted to smoking at the time of the survey compared with 26.2% (95% CI = 21.6%, 31.4%, n = 157) of non‐vapers (Wald F = 5.95, P = 0.015) (Supporting information, Table S2 ). This relationship remained after adjusting for covariates (aOR = 2.89, 95% CI = 1.58, 5.30, χ 2 = 11.87, P < 0.001) (Table 2 ). Additionally, among all former smokers, those who had quit in the last 3 months were more likely to report feeling very addicted compared to those who had quit 1–2 years ago, as were older (55+) compared to younger age groups, and white former smokers compared to non‐white former smokers.

Among vapers, 74.4% (95% CI = 64.5, 82.5, n = 368) reported that they used to smoke more than 10 cigarettes/day compared to 47.2% (95% CI = 41.9, 52.6, n = 318) of non‐vapers (Wald F = 22.37, P < 0.001) (Supporting information, Table S2 ). This difference remained after adjusting for covariates (aOR = 4.39, 95% CI = 2.22, 8.68), χ 2 = 18.18, P < 0.001) (Table 2 ). Additionally, among all former smokers, those who had quit less than 1 year ago were less likely to report that they smoked more than 10 cigarettes/day compared to those who had quit 1–2 years ago; similarly, those aged less than 40 versus those aged 55+, those with high versus moderate education, males versus females and those of non‐white ethnicity versus white ethnicity were less likely to report smoking more than 10 cigarettes/day (Table 2 ).

Among vapers, 34.3% [95% confidence interval (CI) = 25.6, 44.3, n = 138] reported that they used to smoke within 5 minutes of waking compared to 15.9% (95% CI = 12.2, 20.6, n = 84) of non‐vapers (Wald F = 11.26, P < 0.001) (Supporting information, Table S2 ). This difference remained after adjusting for covariates [adjusted odds ratio (aOR) = 3.74, 95% CI = 1.99, 7.03, χ 2 = 16.92, P < 0.001] (Table 2 ). Additionally, among all former smokers, those who had quit 4–12 months ago were less likely to report that they used to smoke within 5 minutes of waking compared to those who had quit 1–2 years ago, and 40–54‐year‐olds were more likely to report having smoked within 5 minutes of waking compared to those aged 55+ (Table 2 ).

Of the 1070 former ever daily smokers, 245 were from Canada (CA), 171 United States (US), 261 England (EN) and 393 Australia (AU) (Suppor ting information, Table S1 ). Overall, 440 (41.1%) were classified as daily nicotine vapers (vapers) and 630 (58.9%) were current non‐vapers. Of the 1070 former smokers, 54% were male, 90% white ethnicity, 49% high income and a fifth (20%) had quit in the last 3 months, 39% 4–12 months ago and 40% 1–2 years ago. There were significant differences between vapers and non‐vapers on country and sample source, but not socio‐demographics (Table 1 ). While just under half of the vapers (44.5%) had quit 4–12 months ago, compared with 34.1% non‐vapers, the differences in time since quitting across the two groups were not statistically significant. Among the non‐vapers, 24.8% ( n = 166) had previously been at least weekly vapers, 17.9% (107) had vaped only occasionally, 8.3% (51) had vaped only once and 49.0% (306) had never vaped. The regression models were based on 1009 to 1051 respondents when taking into account missing data.

Figure 1 gives an overview of the analytical sample. We began with the core sample of 13 099 participants and excluded 8201 daily and 2666 non‐daily smokers, 80 non‐smokers, 804 former smokers who had stopped smoking more than 2 years ago (because they were not assessed on cigarette smoking dependence measures), 175 who smoked less than daily before quitting, 70 former smokers who vaped less than daily, 28 who reported that they did not vape nicotine and five who responded don't know/refused to the nicotine strength questions. This resulted in an analytical sample of 1070 former smokers who had ever smoked daily.

Discussion

When comparing retrospective reports of time to first cigarette and usual daily cigarette consumption between former smokers who vape daily and non‐vapers, significantly more vapers reported that they used to smoke within 5 minutes of waking and smoked more than 10 cigarettes per day, compared with non‐vapers. Vapers were also significantly more likely to perceive that they were still very addicted to smoking (at the time of the survey) compared with non‐vapers, although there was no difference in reporting any urges to smoke. Furthermore, vapers were more likely to report feeling extremely confident in their ability to remain a non‐smoker than non‐vapers. There were few country differences in these measures. As might be expected, the longer respondents were quit the less likely they were to report any urges to smoke in the last 24 hours, the less addicted they saw themselves as being and the more confident they were in staying quit. Curiously, however, those who had quit for less than 1 year were less likely to have smoked more than 10 cigarettes per day, and those who had quit from 4 to 12 months less likely to report previously having smoked within 5 minutes of waking, compared with those who had quit for 1–2 years.

Our finding of retrospective reports of higher dependence among former smokers who vape, compared with those not currently vaping, is novel, but consistent with studies that reported higher retrospective smoking dependence among vapers than dependence in continuing smokers 8. Similarly, in convenience samples of former smokers 17, vapers had a higher smoker identity (agreement with the statement ‘Smoking is a part of me’) than NRT users. However, we were surprised at the relatively high proportion of our sample who perceived still being very addicted to smoking among both vapers (41%) and non‐vapers (26%), especially because approximately 80% of the sample reported quitting smoking more than 4 months ago. There is little literature on this, but just over 50% of smokers who had maintained abstinence for more than 4 years reported some occasional craving for cigarettes 38, and dreaming about smoking was apparent one year after quitting in another study 39.

There are two possible explanations for these findings which cannot be distinguished, given the cross‐sectional nature of the study. First, in line with our finding of higher reported prior dependence on smoking among vapers than non‐vapers, it could be that those former smokers who were daily nicotine vaping at the time of our survey had been a more highly dependent group of smokers. Secondly, that vaping was providing more potent cues for smoking than among the non‐vapers, or vapers were exposed to more friends/family who smoked or vaped, and this maintained their desire for cigarettes. Indeed, qualitative research has found that some people were turned off by the similarity of smoking to vaping, as by replicating the hand‐to‐mouth action of a cigarette too closely, vaping was therefore not breaking the psychological habit of smoking 12. In our study, however, despite higher perceived current dependence on smoking among vapers, there was no difference in the likelihood of reporting any current urges to smoke, suggesting that rather than cueing smoking, vaping might be helping to ameliorate urges, which are known to predict relapse after 1 month of cessation 29. Additionally, vapers were significantly more likely to feel extremely confident in remaining quit than non‐vapers, even after controlling for duration of abstinence, and this self‐efficacy measure has been shown to be protective of relapse 29. In totality, therefore, our findings favour the first explanation, that in our sample the daily vapers had been a more highly dependent group than the non‐vapers, which would support the suggestion that vaping might be offering a novel route out of smoking for this group of smokers, albeit maintaining their nicotine addiction. Our findings should be used to inform longitudinal studies to investigate these relationships prospectively.

One other implication of our findings is that if those who vape after quitting were more dependent before quitting, then we should not be comparing quit rates as a function of use of vaping in population studies, as this study provides evidence suggesting that vapers are distinctly different on factors known to influence cessation success.

The mechanisms behind any effect of NVP for supporting more addicted smokers require elucidation. Vaping may be playing a role in ways other than simply nicotine substitution across the complex relapse trajectory 40. While dependence has been shown to be a predictor of relapse to smoking, recent studies have demonstrated that it is only predictive in the first few weeks of quitting 29, 41, 42, whereas other factors such as urges to smoke, self‐efficacy and friends’ smoking have greater predictive value in later stages of quitting 29, 42. Our findings support other research suggesting that NVP help to combat urges to prevent relapse to smoking 15, but also suggest that NVP may increase smokers’ confidence that they can remain quit. This is possibly because vaping is mimicking aspects of smoking, including positive aspects, in a way that NRT does not 12, 13. There is little research on self‐efficacy and NRT use post‐quitting, although one study found no significant increase in self‐efficacy with NRT use after the quit attempt 43. The most recent Cochrane review for relapse prevention 44 found some evidence for extended use of varenicline but not for NRT, although NRT appeared to be useful for those who had quit without support. A prior review 45 also found that NRT use can be effective in preventing relapse following a period of abstinence. Given that NVP use is increasing among long‐term ex‐smokers over time compared with NRT use, at least in England 46, relapse prevention studies comparing vaping and NRT are warranted. Furthermore, studies of NVP over long‐term abstinence are required, building on the recent randomized controlled trial evidence in which more quitters continued to vape than continued to use NRT longer‐term 15.

This study has important limitations. The methodology for the 4CV1 data 31 relied on commercial databases, only some of which were sourced from probability samples, and we also included an Australian supplementary dedicated vaper sample from which the majority of the vapers in the current study were sourced. We tested whether sample source significantly affected the results and found it did not, although confidence in quitting was significantly greater among the Australian supplementary sample after controlling for other variables. In addition, we included only daily vapers who vape with nicotine, so our findings might not apply to occasional vapers or those who do not vape with nicotine. Because the data analysed in this paper are cross‐sectional, with two measures being retrospective, we cannot separate cause and effect nor can we be confident of the accuracy of the retrospective reported measure, as current vaping status might influence respondents’ recall of their prior dependence, and these findings were not as expected in relation to time since quitting. Finally, sample sizes were insufficient to explore whether any former smokers had used NVP on their last quit attempt and compare this between the two groups. However, this is the first study to compare different groups of former smokers, using the same retrospective and current measures of smoking dependence, as well as confidence in remaining quit.