Ever use

In large surveys, use of ENDS was low but increasing. Only 1% of US adults surveyed in 2009 had tried ENDS.58 Prevalence of use among the general US adult population was higher but still minimal (2%–3%) when assessed in 2010 in four national surveys with probability samples.58–60 ,67 In all of these studies, more current smokers had tried ENDS than former smokers or never smokers.59 ,60 ,67 Rates of use in the USA continued to rise in 2011 (6% overall) with the same gradient pattern by smoking status (1% of never smokers, 7% of former smokers and 21% of current smokers).60 Demographic correlates of use varied across studies. When these studies limited their samples to only smokers, ENDS use was unrelated to history of quit attempts in two studies,58 ,59 but smokers in one study who intended to quit in the next 6 months were more likely to have tried ENDS than smokers with no intention to quit.59

Multiple studies included only current and former smokers in their samples. Across the four countries surveyed by ITC, 8% of current and former smokers had ever tried ENDS.61 Daily heavy smokers had the highest use and long-term quitters had the lowest use. ENDS users were not more likely to have quit smoking since the previous wave of the ITC survey than non-users. Overall, 20% of adult US smokers had tried ENDS when surveyed as part of a 2011 probability panel.68 Unsuccessful quitters were more likely to have tried ENDS than those who had never tried to quit. In another probability panel of US smokers, 10% of cigarette-only smokers had tried ENDS, but 24% of dual cigar and cigarette users had done so.69 Current smokers in the Legacy Longitudinal Smoker Cohort were more likely to have tried ENDS than former smokers (6% vs 3%, respectively).59 Li and colleagues found that 7% of current smokers and recent quitters in New Zealand in 2011 had ever purchased ENDS (a proxy for use).70 Finally, in the most recent survey of ENDS use in 2012, 22% of current smokers in the UK had ever tried ENDS, compared with 4% of former smokers and <1% of never smokers.62 In many of these studies of current and former smokers, women61 ,68 and younger participants59 ,61 ,62 ,68 ,70 had higher rates of use than men and older participants. In some studies, ENDS use was not associated with quit attempts59 ,70 or quit intentions.59 ,61 ,68

In surveys with probability samples, use of ENDS by adolescents and young adults varied considerably by region and year, from less than 1% (US male adolescents in 2011 and Korean adolescents in 2008)63 ,66 to 21% (Polish high school and university students in 2010–2011).64 In other surveys with probability sampling, 5% of college students in North Carolina71 and 7% of young adults in the Midwestern US had tried ENDS.65 In general, the higher rate of ENDS use among Polish youth compared with US youth may relate, in part, to higher population-wide rates of tobacco use in Poland than in the USA.72 ,73 Across studies of youth, men,63–65 ,71 smokers63–65 ,71 and those with important others (friends, family or partners) who smoked64 ,65 were often more likely to have tried ENDS than their counterparts. In at least two studies, the relationship between ever use of ENDS and smoking status should be interpreted with caution due to the very low prevalence of smoking in the sample.63 ,66

Other reported rates of ever use of ENDS are difficult to interpret because of the nature of their samples. For example, 85% of a convenience sample of adults surveyed by Etter and Bullen had used ENDS, but the majority of their participants were recruited through online ENDS forums.44 Among callers to seven tobacco quitlines who responded to a follow-up survey (35% response rate), 31% had ever tried ENDS, and users were less likely to have quit smoking since their initial call to the quitline than non-users.74

Current use

Adults consistently reported low current use (ie, in the past 30 days). Around 1% of respondents were current ENDS users in three 2010 US national, probability-based surveys.58 ,59 ,67 As with ever use of ENDS, current smokers were more likely to be current ENDS users than either former or never smokers.58 ,59 ,62 In surveys limited to current and former smokers, rates varied from 3% (across four countries in the 2010–2011 ITC survey)61 to 8% (USA in 2011).68 In a convenience sample of callers to tobacco quitlines, 9% of current and former smokers reported that they currently used ENDS some days or every day.74

Youth also reported low current use. Only 1% of young adults in the Midwestern USA65 and 2% of North Carolina college students71 were current ENDS users in 2010–2011 and 2009, respectively. Possibly reflecting the overall higher rates of smoking in Poland compared with the USA, a higher percentage of high school and university students (7%) were current ENDS users.64

Dual use

In population-based surveys, most current (or past 30 days) smokers were not current (or past 30 days) ENDS users. In two 2010 probability samples of US adults, 4%59 and 6%58 of current smokers had used ENDS in the past 30 days. More than 11% of those who were current users of more than one tobacco product (eg, cigarettes, cigars, snuff, hookah) had used ENDS in the past month.58 In another probability sample, 11% of Polish youth and young adults who were current smokers had used ENDS in the past 30 days.64 In a large survey with UK adults based on an opt-in survey panel, 3% of daily smokers in 2010 and 7% of daily smokers in 2012 used ENDS.62

Dual use of ENDS with regular cigarettes was fairly common in convenience samples. In surveys with convenience samples of dedicated ENDS users, 12%–34% of ENDS users were current smokers.42 ,44 ,46 ,47 Of 179 ENDS users, 6% used hookah, snuff or some other non-cigarette tobacco product.47 However, among a sample of people who had bought ENDS 6 months earlier, 35% of current ENDS users did not smoke cigarettes, suggesting up to 65% dual use.48 Finally, in three prospective trials with convenience samples, dual use of ENDS and regular cigarettes appeared to be common, with some of the smokers who reduced their consumption of cigarettes continuing to use ENDS at the end of the study.75–77

Amount and duration of use

Daily use among ENDS users was common43–47 ,55 in all but two studies.48 ,74 It is difficult to further quantify the amount of use because, unlike regular smoking which can be measured by the number of cigarettes smoked, ENDS use has no clear metric. An individual does not usually ‘vape’ an entire cartridge of one ENDS in a single sitting. Some studies quantified use by estimating puffs per day (range 120–236),42–45 while others reported the number of bouts of use per day (median of 20 per day46 or 67% use more than 15 times per day).47 Measurements of the number of e-liquid cartridges (range 0–4)75–77 or millilitre of e-liquid used per day (range 3–5 mL)42 ,55 are difficult to interpret because cartridges leak, vary in strength both within and across brands, and require different levels of vacuum to inhale.3 ,12 ,78 Another metric for quantifying use is puff duration. Two studies, one in a laboratory55 and one that examined 73 YouTube videos,22 found that ENDS users take longer puffs on ENDS than conventional smokers do on regular tobacco cigarettes.

Ten studies reported how long participants had been using ENDS.42–47 ,50 ,55 ,74 ,79 Estimates varied from less than 1 month of prior use for 62% of callers to state quitlines74 to a mean of 13 months of use in a convenience-based survey of experienced ENDS users (n=104) conducted in 2011.46 We are not aware of any data about the extent or amount of use of disposable ENDS, although five studies described the use of modified ENDS (sometimes called ‘mods’) or personal vapourisers that do not mimic the appearance of regular cigarettes.42 ,46 ,49 ,50 ,79

Cost

ENDS users’ experiences with the cost savings from using ENDS in lieu of regular tobacco cigarettes are inconsistent.43 ,50 In open-ended survey questions, some participants in a convenience sample survey of ENDS users (n=81) said that they found ENDS to be less expensive than cigarettes (10 comments), while others said they were too expensive (14 comments).43 Most dedicated ENDS users interviewed at a convention (n=15) found them less expensive than cigarettes.50 Finally, among Czech smokers who had tried but stopped using ENDS, 13% did so because they found ENDS to be too expensive.51

Gateway use

Among the 179 Polish ENDS users surveyed online in 2009, 25 reported that they were non-smokers when they previously began using ENDS. Of those, 20% (n=5) currently smoked cigarettes at the time of the survey.47

Health and safety

Many users report positive changes in their health after they begin using the product. In surveys, interviews and case reports, users often describe improved breathing,42 ,43 ,50 less coughing,42 ,43 ,50 fewer sore throats,43 and improvements in overall health and fitness.43 ,50 ,80 In one case report, switching from cigarettes to ENDS alleviated a patient's previously elevated white blood cell count (neutrophilia).81

Some users also report experiencing side effects from using ENDS. As of the first quarter of 2012, the FDA had received 47 reports about adverse events related to ENDS use.82 Of these, they classified eight as serious adverse events, including pneumonia and chest pain, and 39 as minor, including headache and cough. Of the 405 health effects reported by users in an online ENDS forum, 326 were negative; the most frequently reported problems were in the mouth, throat, respiratory system and neurological system.83 One case report described a patient developing lipid pneumonia,84 and another described a patient experiencing heart arrhythmia from using ENDS.85

In surveys with non-probability samples, laboratory research and other case reports, the majority of reported side effects were minor, including mouth or throat irritation/dryness,42–44 ,53 cough,47 ,80 ,86 vertigo,43 ,53 headache43 ,47 ,53 and nausea.43 ,53 In three prospective trials in which smokers tried ENDS for 6 or 12 months, there were no serious adverse events.75–77 Many of the minor side effects experienced at baseline, including cough,75–77 mouth and throat irritation,75 ,77 and headache,76 ,77 lessened considerably or resolved completely by the end of the study period.

Quitting or reducing tobacco use

Although successful quitting was generally not associated with ENDS use in large surveys,58 ,61 ,68 ,74 in convenience sample surveys, focus groups, case studies and interviews with dedicated ENDS users, they often reported that using the product helped them quit smoking42–44 46–50 ,80 ,81 ,86 or significantly reduce tobacco use,42 ,44 ,48 often despite being heavy smokers or having failed quit attempts in the past.43 ,44 ,46 ,48–50 ,80 ,81 ,86 Unlike quitting smoking, reducing smoking may not represent a positive public health outcome, given that it may indicate dual use of ENDS and regular cigarettes.

Only three longitudinal studies have examined smokers’ use of ENDS to quit smoking. Two of the three prospective trials were uncontrolled. In the first, a 12-month trial with 14 patients being treated for schizophrenia, seven of 14 participants reduced their smoking by at least 50% and two others quit smoking entirely.76 In the second, a 6-month prospective trial of 40 smokers, 13 were lost to follow-up, 13 reduced their cigarette consumption by at least 50% and an additional nine participants quit smoking entirely.75 Another prospective trial randomly assigned 300 smokers to use either ENDS with nicotine or ENDS without nicotine.77 At the end of the 12-month period, 11% of smokers using ENDS with nicotine had quit and 10% reduced their cigarette consumption by at least 50%, while 4% of the non-nicotine group had quit and 12% had reduced their consumption. More than a third were lost to follow-up. The differences in cessation between groups were not statistically significant. The results of these trials should be interpreted with caution given that only one randomised participants to conditions (and it did not include a comparison condition with an alternative quit aid), and all three relied on convenience samples in a limited geographical setting.

Restrictions on smoking

The extent to which smokers use ENDS to avoid smoking restrictions was not clear. About a third (36%) of ENDS users in one survey said that they frequently used ENDS in places where smoking was banned.42 In contrast, in another survey of ENDS enthusiasts (n=104) recruited from a convention, 90% said they were able to use where smoking was banned, although they did not clarify how often they did so.46 In a third survey, a substantial number of daily ENDS users from a variety of countries reported using their ENDS at work (71%) or in cafes, restaurants or bars (43%), but it is difficult to interpret these results with respect to avoiding smoking restrictions given that they vary by country.44

Satisfaction

Satisfaction with ENDS that contained nicotine was moderate in most laboratory studies53 ,56 ,57 ,79 and very high in surveys of committed ENDS users.42–44 ,49 ,50 Users often mentioned taste and flavour. For example, more than 90% of users surveyed by Etter and Bullen liked the taste of ENDS.44 Smokers who used ENDS in prospective trials had mixed reactions75 ,77 as did many smokers interviewed in Prauge.51 Finally, in five studies, ENDS users expressed concerns about the quality of ENDS they used, including leaking cartridges or broken components.43 ,44 ,50 ,51 ,75 Some stopped using ENDS because of problems with the devices.44 ,51

Similarity to regular cigarettes

Studies showed little agreement about how much users of ENDS thought they look, feel or taste like cigarettes, as well as whether similarity to cigarettes was a benefit or a drawback. In small focus groups with former smokers (n=11), users mentioned that they liked how using ENDS mimicked the feel of smoking cigarettes, and that they swapped regular cigarettes for ENDS as part of the same daily routines (eg, used after a meal).49 The similarity between the products also made it easier to switch from one to the other. Other ENDS users recruited at a convention (n=15) noted that their desire for ENDS to mimic regular cigarettes had changed over time; although they began using ENDS that looked and felt like cigarettes, most transitioned to using personal vapourisers that did not look like cigarettes.50 In a large convenience sample survey, over a half of the participants said they used ENDS ‘in a similar manner’ as cigarettes.42 A small number of users stopped using ENDS because they did not have the same flavour,43 but others preferred the flavour of ENDS to regular cigarettes.46 During bouts of use of ENDS as part of lab studies (n=20 and n=32), participants’ ratings of ‘mild as own brand’56 ,57 and ‘taste like own brand’57 increased as they continued to use the product. In direct comparisons, about two-thirds of users in separate convenience sample surveys rated ENDS as equally or more satisfying than cigarettes.42 ,47

Withdrawal symptoms, desire to smoke and cravings

ENDS typically provided some relief of smokers’ nicotine cravings and withdrawal symptoms. In six lab studies, participants who had been tobacco abstinent for 2–12 h reported that using nicotine-containing ENDS reduced their desire to smoke or cravings during their inlaboratory use session,53 ,56 ,57 ,79 ,87 ,88 although this was not true in one study.54 In some cases, this reduction was shown to be greater for nicotine-containing ENDS than for non-nicotine ENDS53 ,87 ,88 or for just holding unlit regular cigarettes or ENDS.56 ,88 Interestingly, this reduction in desire to smoke or lessening of cravings occurred even in some cases where objectively measured nicotine uptake was low or modest.53 ,56 Evidence for the alleviation of specific withdrawal symptoms in these lab studies was inconsistent.53 ,56 ,57 ,79 ,87 ,88

Dedicated ENDS users frequently reported that using ENDS successfully reduced their cravings to smoke and some withdrawal symptoms.42–44 ,46 ,49 ,50 For example, experienced vapers interviewed at the Midwest Vapefest ‘routinely described relief of nicotine cravings within 5 minutes of vaping’ and said they could comfortably go long periods of time between bouts of use without experiencing withdrawal symptoms.50 However, in a large online survey with current and former users, 33% of users said they stopped using because ENDS did not reduce their cravings.44 Finally, in the three prospective trials in Italy that followed smokers who began using ENDS for 6–12 months, participants experienced few or no withdrawal symptoms.75–77

Cost

ENDS users’ beliefs about the cost savings from using ENDS in lieu of regular tobacco cigarettes are inconsistent. In multiple convenience sample surveys from the USA and other countries, a small per cent of users said they first tried or used ENDS for cost savings,42 ,43 ,47 ,74 although a much higher per cent reported this reason in another convenience sample survey.44 More than half (53%) of UK smokers, including a mix of users and non-users, believed that ENDS might be too expensive.62

Gateway use

One study documented beliefs about ENDS as gateways to use of tobacco products. Young adult smokers and non-smokers in focus groups in Minnesota, USA, believed that ENDS and other novel tobacco products, including snus and dissolvable tobacco, might appeal to non-smokers who have ‘always wanted to know the feeling of a cigarette’.89 They felt that these products could lead non-smokers to become smokers.

Health and safety

Many users believe that ENDS are healthier than regular cigarettes for themselves42–44 ,46 ,47 ,49 ,50 or for others,46 and they use ENDS for this reason. For example, of 179 Polish adult ENDS users in a convenience sample, 82% believed that ENDS were less dangerous than cigarettes, and an additional 15% believed that ENDS were ‘absolutely safe’.47 Typically, only a handful of users are concerned about the potential negative health effects or toxicity of ENDS.43 ,44

Respondents in surveys that include non-users generally indicate slightly less confidence in the healthfulness of ENDS. In three probability sample surveys of adult current and former smokers, 70%–85% of those who were aware of ENDS believed they were less harmful than regular cigarettes.59 ,61 In a non-probability survey of adult smokers in the UK, 71% held this belief, although 21% still felt that ENDS might not be safe enough.62 Only a third of adult New Zealand smokers believed that ENDS were less harmful than regular cigarettes.70

In multiple studies of students and young adults, 23%–55% believed that ENDS were safer than regular cigarettes.64 ,65 ,71 In focus groups, young adults who had never tried ENDS expressed mixed beliefs about whether ENDS were equivalent to or less harmful than regular cigarettes.89

Examining Twitter accounts related to smoking cessation, Prochaska and colleagues also found a range of beliefs about the healthfulness of ENDS, including tweets with health warnings as well as tweets touting health benefits.90

Quitting or reducing tobacco use

The majority of ENDS users believe that ENDS can help people quit or reduce smoking, and they often use ENDS themselves for this reason.42–44 ,46 ,47 ,49 ,61 ,62 ,74 ,80 Two surveys with probability sampling described beliefs about the cessation properties of ENDS. Among Midwestern young adults (ages 20–28), almost half (45%) of those who had heard of ENDS agreed that they can help people quit smoking.65 A third of New Zealand smokers believed that ENDS could help smokers quit, and 58% said they would be willing to try ENDS for that reason.70

In two studies in which researchers provided smokers with ENDS (both n=40), these smokers later said that they would recommend ENDS to friends or family who wished to quit smoking.53 ,75 Some commercial and personal Twitter accounts also promoted ENDS as a quit tool.90 Finally, in focus groups of young adult non-users (n=66), participants expressed differing opinions about whether ENDS could be used as a cessation device, and some spontaneously recounted anecdotes about people they knew who quit smoking using ENDS.89

Restrictions on smoking

ENDS users have conflicting beliefs about using ENDS to avoid smoking restrictions. In some surveys, only a small per cent of users describe this as a motivation.42 ,43 ,47 ,74 However, in other surveys, more than 40% of respondents said they used ENDS for this reason.46 ,61 ,62

In small focus groups, non-users noted that an advantage of ENDS and other novel tobacco products (snus, dissolvable tobacco) is the ability to get around smoking bans and use them in places where one cannot smoke.89

Satisfaction

Some vapers use ENDS for the pleasure of the experience.43 Smokers who have not tried ENDS had mixed opinions about their potential satisfaction. About one third believed that ENDS might taste unpleasant.62

Similarity to regular cigarettes

Some smokers and users liked that ENDS resembled or felt like regular cigarettes, while others considered this a drawback.42 ,43 ,62 ,74 Certain elements of the vaping and smoking experiences were clearly different. Because ENDS are more complex than cigarettes, interviewed users (n=15) noted that, unlike cigarettes, they required a learning curve to use properly.50 In focus groups, some young adult smokers mentioned that the social experience of smoking might not be replicated with ENDS.89

Withdrawal symptoms, desire to smoke and cravings

Beliefs about the addictive properties of ENDS vary. About a quarter of Midwestern young adults, most of whom were non-users, believed that ENDS are less addictive than regular cigarettes.65 In contrast, in an internet-based survey of a convenience sample of Polish ENDS users, 60% believed that ENDS were less addictive than regular cigarettes, and an additional 7% believed that ENDS were not addictive at all.47 However, more than a half believed they were addicted to ENDS.

Very few (8%) ever users in another online survey said they were afraid of becoming addicted to ENDS, although 4% of the sample stated that they used ENDS because they were unable to stop using them.44 More than half (60%) of UK smokers, only some of whom had used ENDS, believed that ENDS might satisfy the desire to smoke.62 Indeed, some vapers used ENDS to relieve their cravings or alleviate their withdrawal symptoms.43 ,44 ,46 ,50 ,74

Other beliefs

Three other important themes emerged in the literature. First, concerns about personal appearance (eg, preventing yellow teeth) or odour (eg, clothes not smelling like smoke) sometimes motivated interest in or use of ENDS.43 ,44 ,47 ,49 ,50 ,62 ,75 ,89 Second, ENDS users felt a sense of camaraderie with one another; they gathered at vaping conventions46 ,50 and in online forums where they shared information, recommendations and personal experiences.43 ,49 ,50 However, a small minority of ENDS users were concerned about the social acceptability of ENDS use and felt embarrassed about using the product.42 ,51 University students, few of whom had tried ENDS, viewed ENDS use as more socially acceptable than smoking.52 Third, some ENDS enthusiasts were concerned that the product will be banned.43 ,44 ,50 We did not find any arguments by users that ENDS should be specifically exempted from smoke-free indoor air laws.