At the heart of the debate over e-cigarettes is the extent to which the potential benefits of making available a product that may help people who smoke to quit might be outweighed by several potential risks. Risks identified to date include uptake by never smokers, gateway effects, dangers associated with dual use, discouragement from smoking cessation, relapse to or resumption of smoking, renormalisation of tobacco use, 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
People who use e-cigarettes (vapes) report mixed reasons for vaping. People who have never smoked who vape generally report doing so out of curiosity or for fun. For these people, there is no question that vaping increases harm compared with not vaping, and the central question for public health is the extent to which vaping leads to nicotine addiction, short- and long-term health harms, and, even more concerningly, subsequent uptake of smoking.
People who already smoke who use e-cigarettes commonly report vaping 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 person who smokes eventually quitting tobacco.5 That is, whether use of e-cigarettes increases or decreases
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 people who smoke long term in Australia will die from smoking, quitting prior to age 45 reduces mortality risk close to that of people who have never smoked.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 people who smoke—at least in the first instance—would be to attempt to quit without continuing use of nicotine.
While the relationship between vaping and smoking uptake is clear, the question of causation continues to be debated. E-cigarette use could be a marker in young people who would have gone on to smoke regardless; that is, the relationship between vaping and smoking could be explained by other variables, such as social—environmental factors, or a common genetic vulnerability.33,34,41-46 Research in the US,47 China,48 and Australia49 does demonstrate that adolescents who are susceptible to smoking are significantly more likely to report e-cigarette use; however, several studies have also noted smoking uptake among e-cigarette users who would generally be considered least at risk of smoking.50-55 E-cigarette use is associated with an increase in smoking, even among adolescents not susceptible to smoking, and even when studies control for a range of factors associated with smoking uptake.52
Several factors appear to affect the strength of the relationship between vaping and smoking uptake among young people. Compared with older teenagers, onset of e-cigarette use at a younger age appears to be associated with increased odds of smoking.14,56-58 The relationship between e-cigarette use and smoking uptake may also be stronger among boys than girls.59,60 As noted above, e-cigarette use is more common among people susceptible to cigarette smoking.47-49,61 Other studies have found that factors such as more frequent vaping,62 higher nicotine content,10 device type,63 mental health symptoms,64,65 White race (compared with Black),66,67 and middle socioeconomic status (compared to low),66 increase the likelihood of transitioning from e-cigarette use to cigarette/dual use. Use of e-cigarettes among youth and young adults may increase consumption of conventional cigarettes and duration of smoking.9,68,69
The relationship between vaping and smoking appears to be bi-directional, such that smoking increases the risk of e-cigarette use, and e-cigarette use increases the risk of smoking.40,70-75 In addition to cigarette smoking, e-cigarette susceptibility and use may also predict uptake of other types of tobacco products,19,76,77 as well as marijuana, alcohol, and other drug use over time.29,78-89 Such relationships may also be bidirectional, with vaping predicting uptake of other drugs.90
Several possible mechanisms of how e-cigarette use could act as a ‘gateway’ to smoking have been proposed.91,92 Vaping among peers, friends and family members may normalise nicotine use, and is related to positive attitudes and susceptibility to smoking.93,94 Another explanation is that vaping could reduce psychological boundaries that operate in defining oneself as either a ‘smoker’ or a ‘non-smoker’. E-cigarette users are able to practise and become accustomed to the behaviours and rituals associated with smoking without the risk or stigma of tobacco smoke, potentially facilitating the transition into a role that would otherwise have been resisted. A third explanation is more biological and involves the effects of nicotine on the brain. Animal and human studies suggest that nicotine is a ‘gateway’ drug, such that nicotine use may lead to particular changes in the brain that prime and enhance responses to subsequent drugs. These effects appear to be even stronger among adolescents.95 Vaping can expose young people to very high levels of nicotine, and nicotine use among adolescents can lead to rapid addiction and impact the developing brain (see Section 18.6.2). Nicotine addiction and its associated changes in the adolescent brain could therefore facilitate smoking experimentation and uptake.39,50 Consistent with this theory, use of e-cigarettes with higher concentrations of nicotine has a stronger association to later cigarette use.10,96
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.97 They note that increases in use of non-cigarette tobacco/nicotine products has increased substantially in the US97 and UK,98 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.99-101 Another contended 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.102 Critics of diversion theory however 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.103,104 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. Several US studies conclude that there was a slower decline in current cigarette smoking among young people following the introduction of e-cigarettes, suggesting that e-cigarettes are not acting as a substitute for cigarettes.105,106 Recent studies in Australia and New Zealand have similarly found that the rate of decline in smoking among young people slowed markedly after the emergence of vaping.107,108
Some researchers have argued that any gateway effect of vaping to smoking is likely to only have a small impact on youth smoking prevalence at the population level.109 A recent cohort study in the US examined the risk of smoking initiation after vaping and additionally, the risk of smoking becoming an established, regular habit. In line with the gateway theory, it found that ever e-cigarette users were about twice as likely, and current users about 4.5 times as likely, to report subsequent established smoking (defined as 100 cigarettes or more in the respondent’s lifetime and smoking currently). This represented non-significant ‘adjusted risk differences’ (calculated as risk with e-cigarette use minus risk without e-cigarette use, adjusted for covariates) of 0.60 percentage points for ever users and 1.79 percentage points for current users.110 Nonetheless, with very recent large increases in vaping among young people in many countries, even small increases in the absolute risk of smoking will translate to thousands of additional young people smoking as a result of vaping. Any changes in the prevalence of smoking among young people—and whether these changes could potentially renormalise tobacco use among adolescents—are likely to be intensely studied over the coming years.
A number of studies have found that people who smoke who use e-cigarettes are more likely to attempt to quit conventional cigarettes,116-126 though one meta-analysis found conflicting results depending on whether the studies were retrospective (which showed increased quit attempts) or prospective (which showed no differences). The authors call for more robust research that can better establish causality.127 Users of e-cigarettes may be more motivated to quit smoking than those who do not use them,10 with research showing that dual users who predominantly vaped (compared with those who predominantly smoked) were more likely to report using e-cigarettes as a cessation aid.128 Though, use of e-cigarettes among people who smoke unmotivated to quit may also prompt quitting thoughts and behaviours.129,130 Research in the US found no association between use of e-cigarettes and attempts to quit smoking among teenagers,131 while among adults, use of e-cigarettes to quit smoking was associated with more frequent quit attempts among people who had tried but failed to quit.126 A longitudinal study in Mexico found that while people who vape were more likely to try and quit smoking, they were no more likely to sustain abstinence.132
The use of e-cigarettes as a cessation aid has increased over time in Australia, and they are now one of the most popular products for people trying to quit smoking.133 Clinical guidelines state that health professionals may consider recommending therapeutic vapes for smoking cessation when a person has been unable to quit using first-line therapies (a combination of behavioural support and registered smoking cessation medicines).134 Major reviews of the effectiveness of e-cigarettes as a cessation aid have been published since 2018 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),135 and the US Surgeon General.136 Overall these major reviews have generally concluded that the use of e-cigarettes containing nicotine may be associated with increased smoking cessation. A systematic review and meta-analysis commissioned by the Australian government and published in 2022 that was considered by Australia’s National Health and Medical Research Council11 concluded that there is ‘limited 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.137
Several systematic reviews and meta-analyses of clinical trials (which provide the highest level of evidence) have examined the effectiveness of e-cigarettes for cessation,36,138-141,104,105 most of which conclude that users of e-cigarettes were more likely to successfully quit than users of NRT36,139,140,142,143 and than those in control conditions (e.g., usual care, counselling, or non-nicotine e-cigarettes).36,139,140,144 RCTs published since these reviews have concluded that nicotine e-cigarettes both in combination with counselling145,146 and ‘unguided’147 may promote smoking cessation. Though several studies have found that among people who smoke receiving behavioural cessation interventions, self-selected use of e-cigarettes (i.e., e-cigarettes were not being studied but were used by some participants) could potentially undermine successful cessation.148,149 This may vary depending on the person’s reasons for vaping, with one secondary analysis of a digital intervention finding that those who vaped but had stopped at follow-up were more successful in quitting smoking than those who did not use e-cigarettes at all. Quitting vaping was more common among those using e-cigarettes as a cessation tool, while continued use was more common among those who reported vaping in smokefree areas.150
The most recent in a series of Cochrane reviews that examine e-cigarettes for smoking cessation was published in 2025, and concluded that there was high certainty evidence that users of nicotine e-cigarettes were more likely to successfully quit than those who used NRT,151 though critiques of the Cochrane review argue that the limited number and methodical issues of included studies do not warrant the strength of its conclusion (i.e., high certainty evidence).152,153 A review of the design of studies examining e-cigarettes for smoking cessation found that such studies vary widely in their duration and samples, and often lack robust compliance measures (e.g. biochemical verification of use status). It also notes inadequate assessment of participant motivation.154 Another Cochrane review of the evidence on all of the major pharmacotherapies for smoking cessation published in 2023 found that the benefits of nicotine e-cigarettes were comparable to those of varenicline and cytisine (see Section 7.16) and likely similar to combination NRT.155 A subsequent RCT also found that nicotine e-cigarettes are equally effective as varenicline for smoking cessation.156 Initial economic analyses also suggest that the provision of e-cigarettes alongside behavioural support may be a cost effective strategy for smoking cessation.157
Some have argued that the increased risk of prolonged dual use among those assigned to e-cigarettes in clinical trials has not been adequately acknowledged or reported.152,158,159 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,160 the long-term health risks of which are largely unknown (see Section 18.6). Authors of one review suggest that that e-cigarettes could be considered on a prescription basis with clinical supervision, and after considering potential benefits as well as risks such as these.161
Population groups identified in national strategies as priorities for reducing smoking prevalence include those that have much higher smoking rates (e.g. people with lower levels of income or education and those with mental illness), or for whom smoking causes unique or disproportionate harms (e.g. people who are pregnant)—see InDepth 9A. Early studies have begun investigating the feasibility of e-cigarettes for smoking cessation among these groups; for example, people experiencing homelessness.162,163
Given the disproportionate burden of smoking-related harm experienced by people with mental illness, some researchers164-167 and organisations168 have advocated the use of e-cigarettes as a smoking reduction or cessation aid for people with mental disorders (see Section 18.6.10 for a discussion of the relationship between vaping and mental health). Some preliminary evidence suggests that vaping may be a helpful smoking cessation aid for people with psychiatric disorders.169-172 An Australian trial comparing nicotine vapes and NRT for smoking cessation among people experiencing social disadvantage who were willing to quit smoking concluded that vapes were more effective.173 A limitation of the trial was that participants only had the choice of either fast-acting NRT lozenges or gum; they were not offered a combination of fast- and slow-acting NRT, a treatment regime known to be more effective in supporting cessation (see Section 7.16). Another Australian trial that did compare combination NRT with e-cigarettes among people with substance use disorders, both combined with Quitline counselling, found promising cessation rates with no differences in effectiveness between the two products.170
A number of recent studies have examined the efficacy of e-cigarettes as a cessation aid during pregnancy (for a discussion of their safety, see Section 18.6.1). An RCT in the US suggests that the timing of e-cigarette uptake may affect smoking cessation. It found that those e-cigarette users who had started vaping before pregnancy had a higher smoking abstinence rate in late pregnancy than NRT users, while new e-cigarette users had a similar smoking abstinence rate to NRT users.174 An RCT in England and Scotland found that e-cigarettes appeared to be more effective than NRT in helping pregnant people who smoke to quit; however treatment adherence and validated abstinence were low.175,176 Longitudinal research in England found that e-cigarette use during pregnancy may be associated with a lower likelihood of returning to smoking postpartum.177
Guidelines in some countries support the use of e-cigarettes as a cessation aid during pregnancy as a last resort for those unwilling or unable to use other medications.178 Due to insufficient information on their effects on foetal development and obstetric outcomes, Australian guidelines do not recommended e-cigarettes as a smoking cessation aid for people who are pregnant or breastfeeding.179
A number of studies have attempted to assess whether some patterns of use of e-cigarettes may be more helpful in assisting users achieve smoking cessation than others. Studies generally find that sustained and frequent e-cigarette users are more likely to reduce cigarette consumption180 or successfully quit119,136,161,181-198 than those who use the products short-term or intermittently. Infrequent e-cigarette users may be less likely to quit, with research showing an association between non-daily use and both lower motivation to quit181 and lower rates of successful cessation.161,184,189,195,199,200 This may be partly explained by research showing that dual users who vape more frequently are more likely than those who vape less frequently to cite quitting or reducing smoking as a reason for vaping.128,201
A recent systematic review of the role of flavours in quitting found low certainty evidence that there is no association between use of flavoured vapes and increased quit intentions or attempts compared to tobacco-flavoured vapes. It also found very low certainty evidence that using non-tobacco flavours did not increase quitting success compared to using tobacco/unflavoured vapes, nor did use of non-menthol and non-tobacco flavours compared to tobacco and menthol-flavoured vapes.202 A secondary analysis of the Cochrane review of e-cigarettes for smoking cessation similarly did not find any clear evidence of an association between flavours and cessation, though noted the paucity of data.203 An update of this review in 2025 reached the same conclusion.204 Use of disposable e-cigarettes may be associated with a lower likelihood of quit attempts and successful cessation compared with other product types.190,191,205,206 Studies have also begun examining the effectiveness of combining e-cigarettes with cessation medications, with some small studies suggesting this approach shows promise.207-209
A number of population-level studies published in recent years have explored the association between e-cigarette use and quit rates in the ‘real world’ (i.e., outside of clinical trials).188,210-213 That is, whether declines in smoking prevalence in some countries can be attributed to the increasing use of e-cigarettes. Initial reviews of research up to 2019 did not find evidence that e-cigarettes increase quitting at the population level.161,214 Several more recent studies in England have suggested that e‐cigarette use is associated with increased rates of successful quit attempts and/or overall quit rates,8,212,215-217 particularly among middle-aged and younger people.218 Cross-sectional research in Australia,219,220 New Zealand,221 the US,222 Germany,223 and in the EU224 has found an association between e-cigarette use and smoking cessation, though research in Italy has not.225 Research in Ireland found that while in 2015 dual use was strongly associated with higher odds of quit intentions and attempts compared to tobacco-only use, in 2023 the relationship between dual use and quitting intentions had substantially diminished, and there was no longer an association between dual use and quit attempts.226
Initial evidence from the longitudinal PATH study in the US found that e-cigarette use was not associated with increased cessation among adults who smoke compared with non-e-cigarette users227-230 or compared with users of NRT or cessation medications.229,231 More recent analyses have found that while rates of quitting were no higher among e-cigarette users in earlier survey years (before 2016), between 2018/19 and 2021 rates of quitting were significantly higher among people who vaped. The authors speculate that increases in frequency of use and changes in product features may account for these differences over time.232,233 Additional cohort studies looking at recent waves have found that daily vaping was associated with increased odds of abstinence among people using e-cigarettes to quit smoking.234,235 However, another analysis of PATH data found that while daily vaping was associated with cessation in unadjusted analyses, once a range of confounders were adjusted for, there was no significant difference in smoking cessation among people who smoked and vaped daily, compared with people who smoked and did not vape. Cessation was significantly lower among people who smoked who vaped non-daily compared with not at all.199
Longitudinal research in Aotearoa New Zealand found that those who vaped were just as likely to transition to smoking as those who smoked were to transition to vaping. The authors suggest that declining smoking prevalence is better explained by other factors such as public education campaigns and increased tobacco taxes.236 Another US PATH study examined transitions between tobacco and e-cigarettes. Among those who smoked, an estimated 2.1 million people transitioned to exclusive vaping or quit smoking by using e-cigarettes (‘beneficial’ transitions), while an estimated 4.6 million people who had never smoked took up vaping or moved from exclusive vaping to smoking (‘harmful’ transitions). That is, for every beneficial transition, there were approximately 2.15 harmful transitions.237 Research in Taiwan238 and the US239 also notes that e-cigarette use does not appear to be associated with smoking cessation among adolescents.
Given the higher likelihood of long-term e-cigarette use among those who use the products as a smoking cessation aid,240 it is important to examine whether such use prevents or facilitates relapse to smoking. Research in England shows an increase over time in the uptake of vaping after successful smoking cessation (i.e. vaping that was not attributable to having used e-cigarettes to quit smoking), including among those who had quit many years earlier.241 Data from the ITC Four Country study showed no differences in relapse in 2018 between ex-smokers who were vaping in 2016 compared to those who were not vaping.242 However, longitudinal studies in France,211 the US,243-248 and the UK249 have found an increased risk of relapse among people who have quit smoking who use e-cigarettes. Some studies have noted differences in relapse risk depending on frequency of vaping and smoking history, with the risk appearing to be higher among long-term quitters than among those who have recently stopped smoking211 and among intermittent users compared with those who vape daily.249,250
A systematic review and meta-analysis published in 2021 found evidence that that people who had quit smoking who use e-cigarettes have more than twice the odds of relapse compared with those who have not used e-cigarettes.13 Another similarly concluded that people who had quit who used e-cigarettes—particularly long-term ex-smokers—had an increased risk of relapse to smoking compared with non-e-cigarette users.251 A further recent industry-funded review concluded that findings on the risk of smoking relapse among ex-smokers who use e-cigarettes are mixed and inconsistent.252 A secondary analysis of studies from a Cochrane review examined longer-term (six months or more) smoking abstinence and relapse following use of e-cigarettes and similarly found contradictory results.253 One study using longitudinal US PATH data suggests that differences in how relapse is defined may affect conclusions, with people who vape appearing to be more likely to ‘slip’ (report any smoking in the past year) but no more likely to relapse (report more recent or frequent smoking).254
Studies examining the effects of quitting e-cigarettes on smoking have produced mixed findings. One study using PATH data in the US found a possible risk of relapse among ex-smokers in the short-term following cessation of e-cigarettes,255 suggesting that NRT may be beneficial to support people who have quit smoking who are attempting to quit vaping. In contrast, a secondary analysis of data from an RCT examining vaping cessation found that quitting e-cigarettes was associated with smoking cessation, even though smoking was not a focus of the trial.256
Reduced daily consumption of conventional cigarettes in users of e-cigarettes have been noted in many studies,124,165,180,242,257-261 and reviews;142,262,263 with some authors suggesting that vaping may play an important role in reducing harm among people who smoke who belong to population groups disproportionately affected by smoking (e.g., low socioeconomic status groups).264,265 However, it will be important to continue examining whether reduced cigarette consumption among those who both vape and smoke increases their chances of smoking cessation.
Even following substantial reductions in cigarette consumption, evidence suggests that the health benefits of reduced consumption are limited. Although people who smoke 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.266 Several large cohort studies have found that people who smoke who reduce their consumption do not significantly reduce their risk of premature death.267,268 Smoking just 1–4 cigarettes per day significantly increases a person’s risk of dying from smoking-related disease.269 The 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.
A number of studies have shown that dual use of NRT and cigarettes can help alleviate the issue of compensation,270-272 leading some to advocate long-term use of NRT in combination with cutting down as a harm reduction strategy.273,274 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.117,266,275 Further, physiological factors beyond compensation are also relevant to the extent to which risk reduces with reduced consumption. Even low levels of exposure to tobacco smoke cause profound changes in cardiovascular function (See Section 3.36 for further detail).
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 people who smoke to by-pass smokefree regulations,282 and this is a commonly cited reason for vaping.283,284 Other people who smoke 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.4,5,285 However, many people who smoke are unsuccessful in transitioning fully from smoking to vaping, despite initial intentions to quit smoking.283
Research has found that continued dual use is a relatively common pattern among adults,286-289 including young adults,290 and studies in the US have shown that among dual users, most predominantly smoke (rather than heavy or light use of both, or predominant vaping).128,291 Recent evidence from the UK found that the most common pattern of dual use was daily use of both products.292 Completely switching from dual use to exclusive vaping appears to be relatively uncommon,293 with several longitudinal studies finding that the majority of dual users transitioned over time to either continued dual use or exclusive smoking.247,287,294-296 A systematic review similarly found that most dual users reverted to exclusive smoking over time.289 Findings from the US PATH study showed that while a larger proportion of dual users transitioned to exclusive vaping in later compared with earlier waves, it was still lower than the proportion who transitioned to exclusive smoking. Further, uptake of dual use among people who smoke was very low, limiting the public health impact of any beneficial trends.297 The increased risk of dual use has been flagged as a concern in clinical trials among people who smoke who are allocated to e-cigarettes.298
While a reduction in health risks seems likely for people who smoke who completely substitute tobacco cigarettes for e-cigarettes,299,300 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 people who smoke 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 people who smoke who continue to smoke at a reduced rate.267,268,301 However, there is no available evidence whether or not long-term e-cigarette use among people who smoke changes morbidity or mortality compared with those who only smoke tobacco cigarettes.9 Exposure to various toxicants may also vary with the patterns of use; i.e., among dual users who predominantly smoke compared with those who predominantly vape.302 Use of e-cigarettes has the potential to introduce independent or additive health risks.10,303 Targeted smoking cessation interventions for dual users have been developed with the understanding that most without such interventions will continue to smoke304—see Section 18.11.
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