Objective To explore among a diverse range of smokers and recent ex-smokers, particularly those from disadvantaged groups, how nicotine-containing products, particularly electronic cigarettes (e-cigarettes), are understood and experienced.
Methods Qualitative study of 64 smokers and ex-smokers in Central Scotland. Twelve focus groups and 11 individual interviews were carried out with a range of purposively selected groups.
Results Nicotine replacement therapies and e-cigarettes were regarded as being very different products. Nicotine replacement therapies were viewed as medical products for smokers who want to quit, while e-cigarettes emerged as an ambiguous product whose meanings are still being negotiated. Participants’ attitudes and intentions about smoking and quitting were especially important in shaping their understanding of these products. Four main interpretations of e-cigarettes were identified: a more satisfying replacement for smoking, an ambiguous but potentially useful device, a less desirable cigarette and a threat to smoking cessation. The acceptability of continued nicotine addiction and the similarity of e-cigarettes to conventional cigarettes were central themes on which participants held conflicting views. There was considerable uncertainty among participants around the constituents and safety of e-cigarettes.
Conclusions Different groups of smokers bring diverse expectations, requirements and concerns to their evaluations and therefore to the potential use of nicotine-containing products. The ambiguity around e-cigarettes in public health debates and medical practice is reflected in the positions and concerns of smokers. There is a need for both clear, up-to-date trustworthy information about their benefits and risks, and stronger regulation.
- Electronic nicotine delivery devices
- Harm Reduction
Statistics from Altmetric.com
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.
Debate over electronic cigarettes or ‘e-cigarettes’i has intensified in International Public Health Policy.1 Rapid increases in sales have been reported in many developed countries over the past 5 years.2–4 E-cigarettes have been hailed as a potentially life-saving tobacco harm reduction tool;5 however, concerns have been raised. Despite a general consensus among tobacco control advocates that e-cigarettes are likely to be much less harmful to health than smoking tobacco,6 ,7 there remain uncertainties about safety, long-term effects and efficacy for smoking cessation.8 Negative public health scenarios are that smokers may use e-cigarettes to maintain rather than reduce their smoking—using them at times they cannot smoke—or that non-smokers (particularly adolescents) will start using them and progress to smoking tobacco.9 Such concerns are intensified by the marketing of e-cigarettes, especially as lifestyle accessories, and by the renormalisation of smoking behaviours due to the similarity of some e-cigarettes with conventional cigarettes.10 Nevertheless, there is a lack of evidence about how the contemporary practice of ‘vaping’ (as e-cigarette use is sometimes known) is evolving. In this context of uncertainty and lack of consensus, it is crucial to understand how smokers view and are using this new technology.
Research on e-cigarettes has focused on these devices’ nicotine delivery characteristics, effectiveness for smoking reduction and cessation, and health and safety issues.8 ,10–16 Studies have also begun to outline patterns of use. Surveys in the USA and the UK report that awareness and use have risen sharply over the past 5 years.3 ,4 ,17 In the UK, a national 2014 survey found that 95% of adult smokers were aware of e-cigarettes, around half had tried them and about a fifth were regular users.18 Common findings from surveys examining use and attitudes are that most smokers believe that e-cigarettes are healthier than tobacco cigarettes, and use e-cigarettes in similar ways to nicotine replacement therapy (NRT), mostly to quit or reduce smoking.2 ,3 ,19–23 There has, however, been little qualitative research on this topic and those studies have focused on committed e-cigarette users and/or were undertaken when e-cigarettes were less prevalent.22 ,24 Little is known about the meanings this contested new technology has for smokers, and how they understand and negotiate the risks and benefits of using an e-cigarette.
In the UK there is fairly strong support for e-cigarettes among tobacco control advocates; minimal regulation (eg, on advertising and age of sale); and increasing use, availability and visibility of e-cigarettes (eg, news coverage, television advertising, e-cigarette specialist shops and displays in newsagents). The qualitative study reported here explored how nicotine-containing products (NCPs), particularly e-cigarettes, are understood and experienced by smokers and recent ex-smokers, asking what understanding do smokers and ex-smokers have of the risks and benefits of different NCPs, and how do these understandings shape their attitude towards and experiences of using the different products. The study included participants with a range of exposure to and experiences with e-cigarettes and focused on disadvantaged smokers, such as those with low socioeconomic status or mental health issues. They have the highest smoking rates but are least likely to quit; harm reduction approaches may be of particular benefit for some of these smokers.25–27 The study's focus on the experience of smokers and recent quitters improves the evidence base and includes voices rarely heard in policy debates.
Interviews of 12 focus groups and 11 individuals were conducted with purposively selected smoker groups. Focus groups were chosen to stimulate discussion of unfamiliar ideas and products and allow participants to draw on a range of experiences and challenge conceptualisations, while interviews enabled exploration of individuals’ understandings in the context of their smoking history and practices. Sampling focused on recruiting different groups who may benefit most from tobacco harm reduction approaches. Young adults (16–25 years) were also included as they have low quit rates and may be particularly interested in novel technologies such as e-cigarettes.
Smokers and recent ex-smokers (quit in previous 12 months) were recruited from community and interest groups serving disadvantaged areas of central Scotland, including National Health Service (NHS) stop smoking groups, employment and retraining programmes for young adults who are not in employment, education or training, support groups for young and/or vulnerable parents, or older adults in need of social support, and a community resource centre for people with mental health problems. Six interview participants were recruited via an advertisement on UK classifieds website ‘Gumtree’. We chose pre-existing groups in order to aid recruitment and stimulate more natural discussion in our focus groups.28 ,29 Our groups were constellated around shared experience (eg, quitting smoking, parenthood, mental health issues) rather than on demographic characteristics, although most groups were fairly homogeneous in age (eg, young adult, mid-life, older adults). Most groups comprised those who knew each other previously, but were not tight-knit circles of friends; they tended to meet regularly, for a limited period of time. Recruitment material explained that the study was exploring ‘people's views and experiences with products that might be used instead of smoking, such as nicotine replacement therapies or electronic cigarettes’, and a £10 gift voucher was offered. Participants were provided an information sheet and consent form and offered the opportunity to ask questions; consent forms were signed. Focus groups were hosted in community venues where participants ordinarily met; interviews took place in locations convenient for participants. The data were gathered primarily by CR between September 2013 and February 2014. Ethics approval was obtained from the Research Ethics Committee of the Centre for Population Health Sciences, University of Edinburgh.
Focus group topic guides were used flexibly. Discussion was initiated by asking what sorts of products participants had heard of. Pictures and examples of different products were then used as prompts to explore experiences with products, price and sources of information. Examples of the three main types of e-cigarettes—disposable, rechargeable and refillable—with a variety of packaging were used. The first two types look and feel like conventional cigarettes and tend to be cheaper initially; the refillable devices are usually larger and more expensive, although cheaper to run. Questions explored the uses, advantages and disadvantages of products and views on regulation. Interview topic guides followed a similar pattern, but started off exploring the interviewee's smoking history and previous attempts to change or stop smoking.
Focus groups and interviews were recorded, transcribed verbatim and imported into NVivo V.10 to facilitate data management. Repeat readings of transcripts were undertaken to develop codes for thematic analysis.30 Codes were then systematically compared in order to identify cross-cutting themes and highlight common experiences, as well as differing views. Particular attention was paid to how participants categorised products, how they thought these should be used, how they talked about risks and benefits, and whether this differed between groups. Themes were discussed between coauthors. Where quotations are used in the Results section, participants are identified by whether they took part in a focus group or interview and an identifier (eg, FG01/Int05), gender (F=female/M=male), age (in years) and smoking status (S=smoker/E=ex-smoker). See tables 1 and 2 below for details about participants and groups.
Most participants viewed their smoking as a form of addiction; however, the ‘habit’ or ‘psychological’ aspect of smoking was strongly emphasised. Many emphasised the role an individual's ‘mindset’ or ‘willpower’ played in quitting smoking and this shaped participants’ views on what NCPs could achieve. Many reported that smoking helped them cope with stress, particularly those with mental health problems. Notwithstanding these commonalities, participants varied as to how they felt about their smoking and quitting in ways that are important for understanding their attitudes towards NCPs (see figure 1 for this ‘Smoker Spectrum’). At one end of the spectrum were those who had been unhappy about their smoking, often for health reasons, and had quit smoking. Then there were those who were dissatisfied with their smoking and were planning to/in the process of quitting, and feeling reasonably confident about this. In the middle were those who were somewhat concerned about their smoking, but had no immediate intentions to stop. Towards the other end were two different groups, those for whom smoking was perceived as playing an important role in relieving stress or anxiety so could not think about quitting at the moment, and those who enjoyed smoking and had no interest in quitting—often young adult smokers.
An ambiguous space between smoking and quitting
Most participants were familiar with a range of NRTs and had some knowledge of e-cigarettes; almost all had tried one or two NRTs. Around half had tried an e-cigarette and eight had used them more long term. For most participants, NRT and e-cigarettes belonged to different categories. NRTs were viewed as medical products for smokers who want to quit. Participants had been prescribed NRT by their general practitioner or smoking cessation advisor, or had bought from a chemist. Common shortcomings of NRT included not seeming ‘to make any difference’ and being expensive. Specific off-putting elements were also reported, for example, NRT gum tasting ‘disgusting’. Sold by trusted retailers, such as pharmacies and prescribed by doctors, NRTs were generally viewed as safe and trusted but not very effective.
In contrast, for e-cigarettes there was uncertainty over their intended purpose and correct use. Participants had predominantly come across e-cigarettes locally: on display in newsagents or supermarkets, promoted in shopping centres, e-cigarette-specific shops, seeing people using them, or through friends/acquaintances who had tried them. Perceived as less obviously about quitting smoking than NRT, e-cigarettes were characterised as occupying an ambiguous space in between smoking and quitting:
The ones that are Nicorette, you would do that if you just wanted to stop smoking and that's it, but the e-cigs, like, you want to stop smoking, but you still want to…have something. (Int03-F-31-S)
Language around e-cigarettes was also in flux, drawing on smoking terminology with the products described as “e-cigs”, “electronic fags”, and more commonly, later on in the study, as ‘vaporisers’; and use of them as ‘using’, ‘smoking’, ‘taking a draw’, ‘puffing’ or, occasionally, ‘vaping’. Regarding the cost, some participants commented that the initial outlay for a reusable/refillable e-cigarette was high; others talked about saving money compared with smoking tobacco.
Interpretations of e-cigarettes
Although there was agreement that e-cigarettes did not fit the category of smoking cessation aid, what sort of product they were was uncertain and contested. Four main interpretations of e-cigarettes were identified: a more satisfying replacement for smoking; an ambiguous but potentially useful device; a less desirable cigarette; and a threat to smoking cessation. These interpretations broadly map onto the participants’ position on the ‘Smoker Spectrum’ (see figure 1 for how they intersect). While these categories were not discrete—participants sometimes combined elements of them in their views—they highlight key positions taken on e-cigarettes and the perceived role of NCPs more broadly.
A more satisfying replacement for smoking
Generally, the participants who were most interested in using, or who were already using, e-cigarettes were concerned about the impact of smoking on their health but saw themselves as addicted and previously had, and/or thought they would, find it very difficult to stop smoking. This included most of those with mental health problems. This group saw e-cigarettes as a substitute for smoking or as useful in cutting down the number of cigarettes they smoked.
These participants thought e-cigarettes were better for their health and this was a key reason discussed for switching. E-cigarettes were considered more satisfying than NRT because of their similarity to smoking, that is, inhaling the vapour, getting a similar ‘hit’ (figure 1) and mimicking the ‘hand to mouth’ action or ritual of smoking. This similarity created ambiguity over whether using e-cigarettes constituted stopping or continuing smoking. A participant who had switched to using e-cigarettes reflected: “I don't feel like I've stopped smoking, I just feel like I smoke them instead” (Int02-F-47-E). E-cigarettes’ potential to save money compared with smoking was also commonly discussed. This group generally saw continued addiction to nicotine as unproblematic if it helped stop smoking.
Downsides to using e-cigarettes were also mentioned by this group, including worries around the safety of products, knowing what they contain and trusting retailers. There were doubts about e-cigarettes’ ability to substitute fully for smoking in what they experienced as relieving stress. For example, when asked why she had switched back from e-cigarettes to tobacco, one participant explained: “Because […] there's a wee bit too much stress in my life at the moment that I had to go back on the cigarettes” (FG08-F-47-S).
An ambiguous, but potentially useful device
Participants whose construal of e-cigarettes fell into this category were a more diverse group, potentially interested in trying e-cigarettes or using them again. They were thinking about making a change to their smoking, but had no immediate intentions to stop. Some thought they might use e-cigarettes in the short term to wean themselves off smoking; others saw them as a cheaper alternative. They considered similar benefits to the previous group: health; possibly easier to switch to because of their similarity to smoking; and saving money. They also raised several uncertainties about these products (figure 1). One issue, common across these different groups, centred on how to use e-cigarettes, and its possible over-use:
I had one of those [e-cigarettes]… You didn't know when to stop. At least with a cigarette you get to the end of it and you stub it out and that's you for the next however long. But with that you could just sit and keep puffing away. (FG1-M-36-E)
Some were unsure how to choose the most appropriate product, talking about a lack of guidance on their effectiveness and there being too much choice. Other uncertainties included self-consciousness about using e-cigarettes in public, particularly among women; whether e-cigarettes’ similarity to smoking might make quitting nicotine altogether harder; and concerns about the safety of these products and what they contain.
‘I would rather smoke a fag’: a less desirable cigarette
Finally, there were two distinct groups who did not interpret e-cigarettes as a useful technology: they fell at opposite ends of the smoker spectrum. The first, while curious about e-cigarettes for their novelty value and interested in different packaging and flavours, were happy smoking and did not see the point of switching to an e-cigarette. These smokers were relatively unconcerned about the health effects of smoking, not currently interested in quitting, and tended to be the youngest participants. There was also some confusion among these participants about whether e-cigarettes are ‘healthier’ than smoking, as box 1 highlights.
Focus group (FG) discussion: “What's the point of smoking that?”
M3, 20-S: Oh, I dinnae like those ones, because they dinnae look like fags [cigarettes]. I only like the ones that look like fags.
M1, 18-S: They're minging [disgusting], but.
M3, 20-S: I just like fags. I just like the taste of fag. […]
M4, 18-S: I've not tried them [Vapouriser]. I tasted the E-lite and it was alright, it tasted like a real fag, but it's heavy as fuck. You walk about like that… it's like metal. I wouldn't use that.
Moderator: Why not?
M1, 18-S: What's the point of smoking that? It's not healthy for you. What's the point? Those fags are just the same, they're not healthy, you might as well just smoke fags.
M3, 20-S: Those ones are alright, man.
M1, 18-S: They're not healthy.
M3, 20-S: They've got tar and carbon monoxide in them.
M1, 18-S: You're still smoking nicotine, but.
M3, 20-S: You're still smoking nicotine, but you're not smoking tar and you're not making your lungs… you're not making your lungs get covered in tar. […]
‘Slippery slope’: a threat to smoking cessation
The second group, which comprised recent ex-smokers who were concerned about the health effects of smoking, viewed e-cigarettes as too similar to smoking. They commonly stressed the importance of willpower and the need to ‘break the habit’ in quitting smoking. Of major concern was the possibility of getting addicted to a replacement product or continued addiction in general. Several participants described a friend or acquaintance who had become ‘addicted to’ a NCP or used it for a longer time than was judged appropriate. Concerns often focused specifically on nicotine, at times linked to uncertainty about whether nicotine is harmful. For others, these concerns were part of a broader discomfort about not being dependent and losing control. A related issue was that e-cigarettes were not a big enough step away from smoking and therefore relapse to smoking tobacco might be easier. This group were, therefore, distrustful of products that were similar to cigarettes:
[…] putting them in packets like that [Skycig] makes them look as if you're still a smoker, it's very much replacing an awful lot of that paraphernalia round about smoking, which isn't encouraging people to stop really, it's encouraging people to try and pretend that they've stopped. (FG3-M-44-S)
New ex-smokers were particularly focused on establishing and maintaining abstinence from tobacco (and nicotine).
The health risks of smoking were particularly salient for some smoking cessation group members who brought up smoking-related diseases or health concerns they were experiencing. They positioned NCPs as short-term tools to address this: longer term use and e-cigarettes’ similarity to smoking challenged this shared narrative. Box 2 illustrates the concerns raised about use of e-cigarettes by this group of participants.
Focus group (FG) discussion: addiction as a risk
M2, 44-S: As part of our cutting down, bought the electronic cigarettes, but the problem is that you sit and puff and puff with them and 10 min later you have a fag [cigarette]… [Agreement]
F2, 56-E: Because you're still puffing, you're still physically…
M2, 44-S: That's what [Cessation advisor] said: it's important to break the habit […]
M1, 50-E: And it was half-hearted, it felt half-hearted having the e-cigarette […] it was like because we weren't stopping you would have one of them and then you would have a real cigarette. […]
F1, 51-E: Somebody I know has replaced cigarettes with e-cigarettes, she's been on e-cigarettes for 3 years…
M2, 44-S: It's still better than smoking…
F1: She's doing it in her work, she's in the back shop, because she's not smoking, she's outside, she's got it in her hand 24/7. So, has she really, psychologically stopped? No, I don't think she could give it up.
Moderator: So, would you be worried about that?
F1, 51-E: To me, she's still a smoker, psychologically, she's still a smoker. She may not be getting the bad effects from the cigarettes, tobacco and that, but she's getting the nicotine, she's still feeding her habit.
(FG3-smoking cessation group)
Safety and trust: a cross-cutting issue
Although most participants positioned e-cigarettes as ‘safer’ or ‘healthier for you’ than smoking, a key cross-cutting concern centred on the safety and health effects of e-cigarettes, for example, whether nicotine was harmful or what was inside, as the response from an e-cigarette user illustrates:
The only thing that worries me is not really knowing what those chemicals, ‘cause you are breathing them in, not really knowing, (1) what they are, and (2), because […] I bought like four of them [refill bottles], for all my friends, and they were all cinnamon but they were all different colours. So, I mean, you don't even know who's mixing them, or what's actually in them, or is one stronger than the other. (Int02-F-47-E)
The conversation below from an cessation group at the opposite end of the Smoker Spectrum raises similar points:
M2: I'd be worried about what is exactly in any of the replacements. […] This has got more warnings on it than a cigarette packet [Reading out warnings on refill bottle].
F1: Maybe if Boots [a UK pharmacy chain] did one or something you might trust it more, but all these…we've never even heard of this company. So I don't know, it just seems a bit…
Some participants compared the uncertainty around e-cigarettes unfavourably to the certainty of knowledge about the damaging health effects of smoking:
Obviously there's not been many tests run on these things, that's why I'm saying I'm sceptical, I'm going, no… I'm all right with my tobacco, thanks very much. I've been smoking that for the past 20 years. I know it's doing me damage as cigarettes do. (FG8-M-50-S)
Concerns about e-cigarettes were often linked to matters of oversight: who, if anyone, is monitoring whether products are harmful to health and whether or not a trusted company is selling them. Some participants linked their worries to e-cigarettes being ‘unregulated’. A few mentioned products being manufactured in other countries as a reason for mistrust; others that promotion of products in shopping malls or on sale in discount retailers or at markets made them wary. Participants discussed the fact that (at the time data were collected) e-cigarettes could not be obtained on prescription or from chemists as a reason for misgivings.
E-cigarettes emerged from participants’ talk as an ambiguous product—occupying a space between smoking and quitting. Participants’ understandings reflect much of the public discourse on e-cigarettes, particularly news media and marketing.9 ,31 Attitudes and intentions about smoking and quitting were important in shaping participants’ understanding of products. While some smokers do consider e-cigarettes to be a valuable tool in stopping or reducing smoking; those wanting to quit but thinking they would find it difficult were most likely to perceive significant benefits from using e-cigarettes. Conversely, ex-smokers, particularly those using NHS stop smoking services, commonly found e-cigarettes threatening to their beliefs about quitting and any new non-smoking identity and did not see a role for them.
The acceptability of continued nicotine addiction and the similarity of e-cigarettes to conventional cigarettes were central themes on which participants held conflicting views depending on their position on the Smoker Spectrum. The key attraction for more dependent participants was e-cigarettes’ similarity to conventional cigarettes, and the performative and sensory elements of smoking. For those towards the other end of the spectrum this similarity was perceived as increasing the risk of relapse as e-cigarettes would not break those aspects of their smoking habit. While the former group seemed unworried about ongoing nicotine addiction, others found dependence itself to be a concern. These ambiguities reflect key tensions within public health policy debates;32 although a study of this type cannot address the question of population harm reduction.
There was considerable uncertainty among participants around the safety, health effects and regulatory oversight of e-cigarettes. For some, while smoking was a taken-for-granted health risk, the uncertainties about e-cigarettes loomed large. Some of these concerns echo misperceptions about nicotine,33 ,34 while others reflect the confusing information about e-cigarettes that smokers are currently faced with.
As a qualitative study undertaken within a particular geographic context, the findings cannot be generalised more widely. Moreover, this is a fast-moving topic and it is only possible to provide a snapshot of views at a particular time. Despite these limitations, the study gives a particular insight into the sort of meanings and concepts smokers use when assessing e-cigarettes. The findings underline that different groups of smokers may bring diverse expectations, requirements and concerns to their evaluations of NCPs. As Hitchman et al35 emphasised, it is crucial that this diversity is foregrounded in policy discussions about e-cigarette products and users. Moreover, the cross-cutting concerns about safety highlight the need for accessible, clear, up-to-date and impartial information about e-cigarettes, which communicates benefits, risks and current uncertainties to health professionals and the public.
The ambiguity around e-cigarettes in public health debates, especially unease about promoting an addictive, unlicensed product and disagreement over whether smokers ought to aim to reduce harm or become abstinent, is mirrored in the positions and concerns of smokers. Moreover, participants’ multifaceted understandings of risk and harm are highlighted; physical health was discussed as one aspect of a complicated set of considerations, including general well-being, mental health, finance and social aspects such as norms and identity. It is necessary, therefore, to engage with smokers’ own understandings and terminology in discussions about products, as well as to consider whether harm reduction or abstinence is the desired end point for individuals. Future research might characterise in more depth the key types of e-cigarette users (eg, current/ex-user; short-term /long term, dual/exclusive use; use explicitly for quitting smoking), and also types of e-cigarettes used (eg, cigalikes, vapourisers, ‘third generation’ products), as well as interrogating and adding more depth to our smoker spectrum.
In this context, it is too early to make definitive recommendations about the use of e-cigarettes. Recent guidance to the Scottish and English NHS has, broadly, taken an appropriately cautious line where e-cigarette use is neither endorsed nor discouraged but advice given.36–38 Stronger regulation is required so that smokers can be confident in their choices and healthcare professionals in the advice they give; in particular, standards for the safety and efficacy of products, and restrictions on marketing messages and images would be appropriate. The recent revision of the European Union (EU) Tobacco Products Directive,39 which comes into force in 2016, will regulate e-cigarettes as either consumer or medicinal products depending on how much nicotine they contain and therefore may allow for the existence of products that will be attractive to different user groups (ie, depending on whether they are looking for a lifestyle product or a smoking cessation aid). However, it also has the potential to confuse users about the quality and safety standards of the products they buy.
What this paper adds
Electronic cigarettes are a highly contested new technology which have received considerable attention in public health policy and media debates. These may have an important contribution to make to tobacco harm reduction, but significant concerns have been raised about their role in tobacco control. However, little is known about the meanings that electronic cigarettes have for smokers or how they understand and assess the risks and benefits of using these. This is the first UK study to explore qualitatively among a diverse range of smokers and recent ex-smokers how electronic cigarettes are understood and experienced.
The findings highlight that different groups of smokers bring diverse expectations, requirements and concerns to their evaluations, and therefore the potential use of electronic cigarettes depends on their current feelings and intentions about smoking and quitting. The ambiguity around electronic cigarettes in public health debates and clinical practice is reflected in the positions and concerns of smokers.
There is a need for both clear, up-to-date, trustworthy information about the benefits and risks of electronic cigarettes, and stronger regulation.
The authors are grateful to all of the study participants who spared time to share their views with them and the various gatekeepers who helped them contact participants.
Contributors CR and AA conceived the study. All authors designed, developed the methods for, and obtained funding for the study. CR coordinated the running of the study and conducted the focus groups and interviews, with support from AA. CR and AA read transcripts and developed the analytical framework. CR drafted the manuscript. All authors contributed to the interpretation of the analysis and critically revised the manuscript.
Funding This study was funded by a Cancer Research UK (CRUK) Tobacco Advisory Group (TAG) project grant (Ref: C3721/A16479). CR and AA are members of the UK Centre for Tobacco and Alcohol Studies (UKCTAS), which is funded by the British Heart Foundation, Cancer Research UK, the Economic and Social Research Council, the Medical Research Council, and the National Institute of Health Research under the auspices of the UK Clinical Research Collaboration.
Competing interests None declared.
Ethics approval Research Ethics Committee of the Centre for Population Health Sciences, University of Edinburgh.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Additional unpublished data will be made available on the ReShare data archive which is part of the UK Data Service.
↵i E-cigarettes are battery-operated devices that produce a vapour (usually, although not always) containing nicotine, which the user inhales.