At the heart of the debate over e-cigarettes is the extent to which the potential benefits of making a product that may help smokers to quit might be outweighed by several potential risks. Risks identified to date include uptake by non-smokers, gateway effects, dangers associated with dual use, discouragement from smoking cessation, renormalising smoking, and allowing the tobacco industry to influence decision-making in public health (see Section 18.8 for a discussion of potential population-level risks and benefits).1-3
Consumers of e-cigarettes report mixed reasons for their use. Dual users of tobacco and e-cigarettes commonly report using e-cigarettes to try and help them cut down or quit smoking, because they perceive it as cheaper and/or healthier than smoking, or because they can vape in places that smoking is not allowed or acceptable4 (see Section 18.12). As indicated in Section 3.36, health risks associated with smoking are unlikely to be reduced by e-cigarettes if users continue to smoke. Crucial to assessing the potential public health benefits of increasing use of e-cigarettes, then, is whether such use will increase or decrease the likelihood of a smoker eventually quitting tobacco.5 That is, whether use of e-cigarettes increases or decreases
- the likelihood of smokers making quit attempts
- the likelihood of a given quit attempt being successful
- the likelihood of reducing use of cigarettes eventually leading to quitting
- the likelihood that use of e-cigarettes among ex-smokers prevents relapse.
Smoking poses a very significant risk to health both in the immediate and the longer term, but the most serious diseases emerge only with long-term use. While two of every three long term smokers in Australia will die from smoking, quitting prior to age 45 reduces mortality risk close to that of never smokers.6 Given that complete cessation of use of any nicotine product is the option associated with least harm, it follows that the optimal approach for younger smokers at least in the first instance would be to attempt to quit without continuing use of nicotine.
This section summarises research examining the relationship between e-cigarette use and smoking, including:
18.7.1 A ‘gateway effect’ to tobacco smoking among young people
Of great concern to public health experts is the growing body of research suggesting a possible relationship between e-cigarette use and the uptake and escalation of smoking among young people, particularly given evidence of increasing e-cigarette uptake among young never smokers.7 Major reviews published by Public Health England,8 the US National Academies of Sciences, Engineering, and Medicine,9 the CSIRO10 and NHMRC11 in Australia, and the Scientific Committee on Health, Environmental and Emerging Risks (SCHEER) in Europe12 have concluded that e-cigarette use increases the risk of smoking among young people. A major review and meta-analysis funded by the Australian Government Department of Health found that never smokers who used e-cigarettes had about three times the odds of smoking initiation compared with non-e-cigarette users.13 Additional longitudinal studies,14-25 and several less extensive reviews26 and meta-analyses,27-34 have similarly concluded that e-cigarette use is associated with an increased risk of cigarette smoking.
Given the consistent and robust evidence, it has become increasingly acknowledged that e-cigarette use increases the likelihood of smoking of combustible tobacco products. However, it is important to recognise while e-cigarettes influence smoking uptake, studies such as those described above cannot establish that e-cigarette use causes smoking. E-cigarette use could be a marker in young people who would have gone on to smoke regardless; it is possible that the relationship between e-cigarette use and smoking could be explained by other variables, such as social—environmental factors, or a common genetic vulnerability.28, 29, 35-40 However, several studies have noted conventional cigarette uptake among e-cigarette users who would be considered least at risk of smoking,14, 41-45 and the best-quality studies and reviews have attempted to control for underlying susceptibility. E-cigarette use is associated with an increase in smoking, even among adolescents not susceptible to smoking.43
There are several factors that may contribute to the risk of smoking uptake among e-cigarette users. Compared with older teenagers, onset of e-cigarette use at a younger age appears to be associated with increased odds of smoking.46-48 The relationship between e-cigarette use and smoking uptake may also be stronger among boys than girls.49 Australian researchers found that, among young adults who had never smoked, curiosity, willingness and intentions to smoke tobacco cigarettes were higher among young e-cigarette users than never users.50 Other studies have found that factors such as more frequent e-cigarette use,51 higher nicotine content,10 device type,52 social anxiety,53 White race (compared with Black),54, 55 and middle socioeconomic status (compared to low),54 increase the likelihood of transitioning from e-cigarette use to cigarette/dual use. Several studies have suggested that the relationship may be bi-directional, such that smoking increases the risk of e-cigarette use, and e-cigarette use increases the risk of smoking.56-59 Use of e-cigarettes among youth and young adults may increase consumption of conventional cigarettes and duration of smoking.9, 60 E-cigarette susceptibility and use may also predict uptake of other types of tobacco products,18, 61 as well as marijuana and alcohol use over time.62-68
Several possible mechanisms of how e-cigarette use may act as a ‘gateway’ to smoking have been proposed. E-cigarette use could normalise nicotine use and smoking behaviours more generally, leading to the renormalisation of smoking. It could also cause users to develop nicotine addiction,34, 41 with research showing that the use of e-cigarettes with higher concentrations of nicotine has a stronger association to later cigarette use.10, 69
In contrast to the gateway theory, some commentators have suggested that, rather than acting as a ‘gateway’, e-cigarettes may be acting as a ‘diversion’ among young people. That is, e-cigarette use partially or wholly replaces cigarette smoking, and may therefore accelerate the decline in youth cigarette smoking.70 They note that increases in use of non-cigarette tobacco/nicotine products has increased substantially in the US70 and UK,71 alongside a decline in cigarette smoking. Several studies from the US have concluded that a long-term decline in smoking prevalence among youth and young adults accelerated after e-cigarette use became more widespread, which the authors argue demonstrates that e-cigarette use has not increased youth smoking at the population level and may support the diversion theory.72-74 Another argued that data on adolescent tobacco/nicotine use from 2000 to 2019 in the US is more consistent with a diversion effect than a catalyst/gateway effect.75 However, critics of this theory argue that continued declines in smoking might alternatively be attributed to the continuing and long-term effects of current and historical comprehensive tobacco control programs.76, 77 To put it another way, declines may have been accelerating due to the cumulative and social contagion effects of previous decades of policy, and may have been steeper still without e-cigarette use. Another US study found that while the introduction of e-cigarettes was followed by a faster decline in ever use of cigarettes among young people, there was a slower decline in current cigarette smoking, which the authors argue suggests that e-cigarettes are not acting as a substitute for cigarettes.78 With very recent large increases in e-cigarette use among young people in many countries, any changes in rates of smoking among young people are likely to be intensely studied over coming months and years.
18.7.2 Effects on attempts to quit smoking
Many smokers report using e-cigarettes as a cessation aid.79, 80 In Australia in 2020, about one in five (22%) smokers or recent ex-smokers reported having used e-cigarettes in their last quit attempt, compared with 27% in Canada, 37% in England, and 22% in the US.81 A randomised controlled trial in Australia reported that e-cigarettes were chosen more frequently than nicotine replacement therapy (NRT) by trial participants (71.1% vs. 29.0%).82 Perceptions that e-cigarettes are less harmful than cigarettes also predict their use as a cessation aid.83 In England in 2018, Cancer Research UK launched an advertising campaign about the relative harms of e-cigarettes compared with tobacco, which targeted smokers aged 25–55 years and lower socio-economic groups. An evaluation of the campaign found that, compared with smokers living in regions not exposed to the campaign, exposure was associated with increased motivation to quit smoking.84
A large study in England found no clear association between e-cigarette use and prevalence of quit attempts; it also found that such use was associated with a decrease in the use of prescription NRT.85 A subsequent English study found that, compared to exclusive smoking, dual use of e-cigarettes was associated with a slightly higher prevalence of quit attempts though this was lower than for dual use of NRT.86 A number of other studies have found smokers who use e-cigarettes are more likely to attempt to quit conventional cigarettes.87-95 This may be due to greater motivation (i.e. smokers who use e-cigarettes are already more interested in quitting smoking than those who do not use them),10 though use of e-cigarettes among smokers unmotivated to quit may also prompt thoughts about quitting.96 Research in the US found no association between use of e-cigarettes and tobacco smoking quit attempts among teenagers,97 while among adults, use of e-cigarettes to quit smoking was associated with more frequent quit attempts among continuing smokers (i.e., those that had tried but failed to quit).98
18.7.3 Effects on success in quitting smoking
Major reviews of the effectiveness of e-cigarettes as a cessation aid have been published by Public Health England,8 the US National Academies of Sciences, Engineering, and Medicine,9 the NHMRC11 and CSIRO10 in Australia, the Scientific Committee on Health, Environmental and Emerging Risks (SCHEER),12 the US Preventive Services Task Force (USPSTF),99 and the US Surgeon General.100 Overall, while highlighting the limited/low quality nature of the evidence, these major reviews have generally concluded that the use of e-cigarettes containing nicotine may be associated with increased smoking cessation (with the exception of SCHEER,12 which found the evidence to be insufficient). Several meta-analyses of clinical trials (which provide the highest level of evidence) have examined the effectiveness of e-cigarettes for cessation,31, 101-104 and generally found weak evidence that users of e-cigarettes were more likely to successfully quit than users of NRT31, 102, 103 and than those in control conditions (e.g., usual care, counselling, or non-nicotine e-cigarettes).31, 102, 103 Several meta-analyses, however, have concluded that e-cigarettes do not appear to be superior to NRT.104, 105 A Cochrane review and meta-analysis published in 2021 found moderate certainty evidence that users of nicotine e-cigarettes were 1.7 times more likely to successfully quit than those who used NRT and also about 1.7 times more likely to successfully quit than those who used non-nicotine e-cigarettes.106
A systematic review and meta-analysis commissioned by the Australian government and published in 2022 was recently considered by Australia’s National Health and Medical Research Council, and a statement by the NHMRC’s CEO assessing that evidence was released on the 23rd June 2022.11 The review concluded that there is ‘limited evidence’ (graded by the NHMRC as “low certainty of evidence”) that, in the clinical context in combination with best-practice counselling and supportive care, freebase nicotine e-cigarettes may be more efficacious for long-term (i.e., >four months) smoking cessation than NRT, and than no intervention or usual care. There was insufficient evidence (graded by the NHRMC as “very low certainty evidence”) that nicotine e-cigarettes are efficacious for smoking cessation compared to non-nicotine e-cigarettes or that non-nicotine e-cigarettes are efficacious for smoking cessation. There was also insufficient evidence that nicotine e-cigarettes are efficacious outside the clinical setting.107
Based on these assessments, the NHMRC advises
“The safety, efficacy and performance of specific products and components are not known, even when they are accessed on prescription. Due to the high level of uncertainty in the evidence of efficacy of e-cigarettes for smoking cessation, smokers wishing to quit should seek further information about e-cigarettes from reliable sources, such as the relevant Commonwealth, State or Territory Health Department, their healthcare practitioner or quit services. There are several other proven safe and effective cessation aids available to try before e-cigarettes.“11
A number of studies have attempted to assess whether some patterns of use of e-cigarettes may be more helpful in helping users achieve smoking cessation than others. Sustained90 and frequent100, 108-120 e-cigarette users appear to be more likely to successfully quit than those who use the products short-term or intermittently. Infrequent e-cigarette users—who comprise the majority of users—may be less likely to quit, with research showing an association between non-daily use and both lower motivation to quit108 and lower rates of successful cessation.111, 116, 117 Analysis of the International Tobacco Control Four Country (Australia, UK, Canada and the US) Smoking and Vaping Survey 2016–2020 found that smokers who initiated daily e-cigarette use were more likely than those who didn’t initiate e-cigarette use to make a quit attempt and abstain from smoking. Non-daily vaping was not associated with any quitting behaviours.121
Some research has found support for the role of sweet/fruit flavours in quitting compared with tobacco or menthol,117, 118, 122 while others have found no differences in quit attempts between users of different flavours.123 Use of disposable e-cigarettes may also be associated with a lower likelihood of quit attempts compared with other product types.118, 119, 124
A number of population-level studies published in recent years have explored the association between e-cigarette use and quit rates.115, 125-128 Several studies in England have suggested that e‐cigarette use is associated with increased rates of successful quit attempts and overall quit rates.8, 127, 129 Cross-sectional research in Australia,130, 131 Germany,132 and in the EU133 has found an association between e-cigarette use and smoking cessation. However, findings from the ITC Four country (US, Canada, Australia, England) study suggest that dual use of cigarettes and e-cigarettes at baseline (2016) was not associated with cessation for either daily or non-daily smokers two years later.134 Research in the US found that e-cigarette use by adolescent smokers was not associated with subsequent abstinence,135 nor does it appear to be associated with increased cessation among adult smokers compared with non-e-cigarette users136-139 or compared with users of NRT or cessation medications.138, 140 A review published in 2020 concluded that while e-cigarettes appear to increase cessation when provided for free within RCTs, at the population level, e-cigarette use as a consumer product is not significantly associated with smoking cessation. The authors suggest that that e-cigarettes could be considered on a prescription basis with clinical supervision, and after considering potential risks and benefits.116 A meta-analysis published in 2022 notes that the use of e-cigarettes for cessation is more likely to lead to extended dependence on nicotine and long-term e-cigarette use,141 the long-term health risks of which are largely unknown (see Section 18.6).
18.7.4 Effects on relapse among ex-smokers
Along with considering the role of e-cigarettes in cessation attempts and success, researchers have begun to consider the relationship between vaping and relapse among ex-smokers. The ITC Four Country study found that while ex-smokers who vaped daily were more likely to perceive that they were still very addicted to smoking, compared with ex-smokers who were not vaping, vapers also reported greater confidence in remaining a non-smoker, which the authors suggest may help to reduce relapse.142 Another paper analysing data from the ITC study found no differences in relapse in 2018 between ex-smokers who were vaping in 2016 compared to those who were not vaping.134 Research in Italy found that among a sample of e-cigarette users who were all ex-smokers, almost two-thirds remained abstinent six years later.143 However, longitudinal research in France found that e-cigarette use was associated with an increase in the rate of smoking relapse among ex-smokers, although the authors note that relapse was not higher among ex-smokers who had quit in recent years.126
Several studies in the US have also suggested that e-cigarette use is associated with relapse among ex-smokers,144-147 with one study finding intermittent users may be more likely to relapse to smoking than those who vape daily.148 Longitudinal research in the US found that while dual use was association with cessation, e-cigarette use had a much stronger relationships with smoking both smoking initiation and relapse.149 Another longitudinal US study found that those who used e-cigarettes to quit smoking were more likely to relapse, though they were also more likely to try quitting again.150 Survey research in South Africa found that odds of relapse for smokers trying to quit were higher among ever, former and current e-cigarette users than never e-cigarette users.151 A systematic review and meta-analysis published in 2021 found evidence that that ex-smokers who use e-cigarettes have more than twice the odds of relapse compared with ex-smokers who have not used e-cigarettes.13 Another similarly concluded that ex-smokers who used e-cigarettes—particularly long-term ex-smokers—had an increased risk of relapse to smoking compared with non-e-cigarette users.152
18.7.5 Cutting down as a step towards quitting
Reduced daily consumption of conventional cigarettes in users of e-cigarettes have been noted in several studies,95, 153-155 and reviews;156, 157 however, this may not lead to meaningful changes in consumption at a population level.158 One study found that although dual use reduced cigarette consumption, total nicotine use and dependence increased, which could hinder the ability to quit either or both products.155 Longitudinal findings from the ITC Four Country surveys showed that among daily smokers, vaping appeared to have been helpful in reducing daily smoking to non-daily smoking, but did not improve rates of quitting.134
Even following substantial reductions in cigarette consumption, evidence suggests that the health benefits are limited. Although smokers who substantially reduce the number of cigarettes smoked per day reduce their exposure to some harmful and potentially harmful constituents, these decreases are limited and much smaller in magnitude than reductions following complete cessation.159 Several large cohort studies have found that smokers who reduce their consumption do not significantly reduce their risk of premature death.160, 161 Smoking just 1–4 cigarettes per day significantly increases a person’s risk of dying from smoking-related disease.162 This modesty of the health benefit from smoking reduction is often attributed to compensatory smoking: those who cut down tend to inhale each cigarette more deeply, and smoke more of it.159, 163 (See Section 3.36 for further detail).
A number of studies have shown that dual use of NRT and cigarettes can help alleviate the issue of compensation,164-166 leading some to advocate long-term use of NRT in combination with cutting down as a harm reduction strategy.167, 168 Researchers have suggested that it may be possible that the use of e-cigarettes while smoking could similarly reduce intake of nicotine and toxins from each cigarette. However, data on the long-term safety of e-cigarettes is lacking, and they may be less safe than existing, licenced NRT products.88
The main benefit of cutting down seems to be its role as a step toward quitting.160, 169 A 2015 review exploring the usefulness of cutting down determined that smokers who reduce the number of daily cigarettes smoked are more likely than smokers who do not cut down to attempt to quit and actually achieve smoking cessation. This is particularly the case when the quit attempt is combined with NRT.170 A 2019 Cochrane review concluded that cutting down may result in similar quit rates to going cold turkey, and that reduction‐to‐quit interventions may be more effective when pharmacotherapy is used, particularly fast‐acting NRT or varenicline.171 NRT-assisted reduction appears to be an effective intervention for achieving sustained smoking abstinence, particularly for smokers not currently intending to quit (or quit abruptly),172, 173 and is effective and cost effective compared to no quit attempt.169 E-cigarettes may similarly prove to be a useful form of NRT in combination with smoking reduction as part of ‘cutting down to quit’, but further research is needed on the efficacy of the products in this context.170 A pilot RCT in Australia that compared abrupt and gradual smoking cessation alongside the use of e-cigarettes among people receiving alcohol and other drug treatment found that while both groups found the intervention feasible and acceptable, adherence was lower in the gradual condition.174
18.7.6 Prolonged dual use of cigarettes and e-cigarettes
Dual use refers to the concurrent use of conventional tobacco products and e-cigarettes. Dual use is actively promoted by some e-cigarette manufacturers, especially those that also manufacture tobacco products, as a way for smokers to by-pass smokefree regulations,175 and this is a commonly cited reason for e-cigarette use among smokers.176, 177 Other smokers use both products as a means of cutting down the number of cigarettes they smoke each day, and/or as an intended pathway to complete smoking cessation.5, 178 However, many smokers are unsuccessful in transitioning fully from smoking to vaping, despite initial intentions to quit smoking.176 One study in England found that long-term use of e-cigarettes was similarly prevalent among current and recent ex-smokers, indicating continued dual use was a common pattern, although this was not associated with reduced motivation to quit.179 Research in the US has also found that continued dual use is a common pattern among adults,180-182 and that among dual users, most are predominant smokers (rather than heavy or light use of both, or predominant vaping). Completely switching from dual use to exclusive e-cigarette use appears to be relatively uncommon,183 with one longitudinal study finding the majority of dual users transitioned to exclusive smoking,181 and another finding that among those intending to quit, dual users were 83% less likely to transition to cessation compared with cigarette smokers only.139 Also in the US, use of e-cigarettes by young adults is associated with more rather than less frequent and intensive cigarette smoking.184 Another English study found that dual users of e-cigarettes had lower quit attempt rates than dual users of NRT,86 and an Italian study found that dual users were no more likely to quit than exclusive smokers six years later.143
While a reduction in risk seems likely for smokers who completely substitute tobacco cigarettes for e-cigarettes,185, 186 the benefits for those who continue to use some tobacco cigarettes are much less certain; as noted above, even ‘light’ cigarette smoking carries substantial health risks—see Section 3.36. Among those who exclusively smoke tobacco cigarettes, cutting down the number of cigarettes consumed may not reduce toxic exposure if smokers compensate by drawing more deeply on the cigarettes they do smoke. There is some evidence that supplementing reduced cigarette consumption with an alternative source of nicotine might reduce toxicant exposure and hence mortality among smokers who continue to smoke at a reduced rate.160, 161, 187 However, there is no available evidence whether or not long-term e-cigarette use among smokers changes morbidity or mortality compared with those who only smoke tobacco cigarettes.9 Use of e-cigarettes has the potential to introduce independent or additive health risks.10, 188 Targeted smoking cessation interventions for dual users have been developed with the understanding that most will continue to smoke.189
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