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Vaping and e-cigarettes

Vaping and e-cigarettes
Literature review current through: Jan 2024.
This topic last updated: Oct 04, 2023.

INTRODUCTION — Electronic cigarettes (e-cigarettes) are battery-operated devices that heat a liquid usually containing nicotine, producing an aerosol that the user inhales (figure 1) [1]. E-cigarettes entered the market in 2003 in China and entered the United States and European markets in 2006 [2]. In many areas, e-cigarettes entered the market as consumer products without government regulation. Initially produced by small companies, tobacco companies have bought some of these companies and are developing these products [3]. They are available both online and in traditional retail outlets.

There is uncertainty about the long-term health effects of e-cigarettes and whether they will help individual tobacco users to stop smoking [4-7]. There are also public health concerns, including concerns about the effect of e-cigarettes on smoking prevalence and their potential use by children as a gateway to nicotine dependence and subsequent combustible tobacco product use [8].

This topic will provide an overview of e-cigarettes, including information about devices, use, components, adverse health effects, use in smoking cessation, impact on public health, as well as suggestions for patient counseling. An overview of smoking cessation and pharmacotherapies and behavioral therapies for smoking cessation are discussed in detail in the following topic reviews:

(See "Overview of smoking cessation management in adults".)

(See "Pharmacotherapy for smoking cessation in adults".)

(See "Behavioral approaches to smoking cessation".)

(See "Prevention of smoking and vaping initiation in children and adolescents", section on 'Vaping nicotine'.)

(See "Tobacco and nicotine use in pregnancy: Cessation strategies and treatment options".)

(See "Cigarette and tobacco products in pregnancy: Impact on pregnancy and the neonate".)

ELECTRONIC NICOTINE DELIVERY SYSTEMS

E-cigarette devices — E-cigarettes are a type of electronic nicotine delivery system (ENDS) consisting of a cartridge containing a liquid, an atomizer (vaporization chamber with a heating element), and a battery (figure 1) [9].

The user activates the atomizer either by inhaling or by pressing a button, depending on the device characteristics. The atomizer then heats and aerosolizes the liquid in the cartridge, creating an aerosol that emulates but is not tobacco smoke. This process simulates the experience of smoking a conventional cigarette, but no combustion occurs. The term "vaping" is used to distinguish the process from smoking a conventional cigarette. The term “dripping” is used to describe a technique in which a couple of drops of the liquid in the e-cigarette cartridge are dripped directly onto the atomizer’s heating element to create a cloud of aerosol that can be inhaled [10].

E-cigarettes originally were designed to resemble conventional cigarettes, but e-cigarette technology is rapidly evolving. Newer versions resemble cigarettes less and feature rechargeable batteries as well as heating elements and refillable cartridges that can deliver higher concentrations of nicotine (figure 2) [1].

First-generation products – First-generation e-cigarettes mimic the shape and size of conventional cigarettes and may be referred to as "cigalikes." They are neither rechargeable nor refillable and are discarded after they stop producing aerosol.

Second-generation products – Second-generation e-cigarettes are larger than conventional cigarettes and are either pen-style (medium size) or tank-style (large size). Both feature rechargeable batteries that may have a switch or electronic circuits that allow users to regulate the frequency and length of puffs or the power delivery to the atomizer. The cartridges in second-generation e-cigarettes are refillable and allow the user to adjust the contents of the e-cigarette liquid.

Third-generation products – Third-generation e-cigarettes are similar to second-generation devices but allow for more custom modifications [1]. They are known as "personalized vaporizers." There are a range of options for cartridges and atomizers; some devices allow the user to adjust the resistance of the atomizer, which produces higher heating temperatures. Users can also pair different atomizers with high-capacity batteries to increase aerosol production and battery life.

Fourth-generation products – “Pod-mod devices” are a type of e-cigarette that has been increasing in popularity among adolescents [11]. These rechargeable devices have replaceable cartridges that contain nicotine and flavorings. A popular brand is JUUL, a device that resembles a USB flash drive. JUUL’s small size and discreet appearance make it easy for the device use to go unnoticed in school settings. JUUL devices can deliver higher concentrations of nicotine without throat irritation because they contain nicotine in a form that is less irritating to the throat.

Novel devices – Similar to first-generation products, these small, often brightly colored devices are non-rechargeable and disposable, and they are available in many flavors (eg, fruit, candy, mint) [12-14].

E-cigarette liquid components — Unlike conventional cigarettes, which burn tobacco and generate smoke, e-cigarettes have a cartridge containing a liquid (sometimes referred to as "vape juice," "e-juice," or "e-liquid"). The liquid is heated to produce an aerosol the user inhales [1]. Nicotine e-cigarettes contain nicotine and other constituents, some with carcinogenic potential [1,15-18]:

Nicotine – The nicotine content of e-cigarettes and liquids varies and usually ranges from none (nicotine-free) up to 36 mg/mL, though it can be higher [1,19]. Common nicotine concentrations of e-cigarette liquids are 6 mg/mL, 12 mg/mL, 18 mg/mL, or 24 mg/mL. Some e-cigarette liquids contain nicotine salts, in which nicotine is combined with an acid [20]. Use of nicotine salts may have a different sensation in a user’s throat [20].

Propylene glycol/glycerol – Propylene glycol or glycerol are humectants that are the main components of most e-cigarette liquids; some products may use ethylene glycol [21].

Flavorings – E-cigarettes may have added characterizing flavors. More than 7000 flavors are available, including candy, fruit, soda, and alcohol flavors [22]. Flavorings may increase the attractiveness of e-cigarettes to youths, especially those who do not already smoke [23].

Metals such as tin, lead, nickel, chromium, manganese, and arsenic have been found in some e-cigarette liquids and aerosol [24,25]. Other compounds detected include tobacco-specific nitrosamines, carbonyl compounds, metals, volatile organic compounds, and phenolic compounds [1,18,26,27]. Vaping devices can be used to aerosolize tetrahydrocannabinol (THC) or cannabinoid (CBD) oils.

Heat-not-burn tobacco products — Another type of heating device is used in heat-not-burn (HNB) tobacco products. The device heats tobacco to a much lower temperature than that of a conventional tobacco cigarette. In July 2020, the US Food and Drug Administration (FDA) approved the manufacturer’s request to market these devices with the claim that they reduce exposure to tobacco toxins [28]. HNB products are described separately. (See "Patterns of tobacco use", section on 'Heat-not-burn tobacco products'.)

PREVALENCE AND PATTERNS OF USE

Prevalence

Adults – The National Health Interview Survey (NHIS), which provides nationally representative estimates of e-cigarette use among adults in the United States, showed an overall increase in the prevalence of current e-cigarette use among adults between 2014 to 2019 (from 3.7 to 4.9 percent), with a transient decline in 2020 to 3.7 percent [29-32] and rebound in 2021 to 4.5 percent [33]. The prevalence of current e-cigarette use is highest among young adults (ages 18 to 24 years), having increased from 7.6 to 11.0 percent between 2018 and 2021. The prevalence of e-cigarette use declines with increasing age [33].

Youth – Between 2013 and 2019, national surveys of middle and high school students in the United States revealed an upward trend in tobacco use in the past 30 days (the measure used to define current use among adolescents), with the greatest increase being in e-cigarette use (figure 3 and figure 4) [23,34-36].

However, the National Youth Tobacco Survey (NYTS) reported a subsequent large decline in e-cigarette use among United States adolescents [14,36,37]. From 2019 to 2021, e-cigarette use declined from 28 to 11.3 percent among high school students and from 11 to 2.8 percent among middle school students, a timing that coincided with the coronavirus disease 2019 (COVID-19) pandemic. The 2022 NYTS reported a partial rebound in e-cigarette use, with 14.1 percent of high school students and 3.3 percent of middle school students reporting current use [38]. Although some of the observed prevalence trends in e-cigarette use during 2021 and 2022 may be attributable to changes in survey methodology, the size of the decline over consecutive years likely reflects some true decrease in prevalence.

Patterns of use — E-cigarette use (ever or current use) is more common among younger age groups, males, and non-Hispanic White adults [32,39-41].

Youth e-cigarette users generally do not use the product daily [42-44]. As an example, in the 2022 NYTS, daily e-cigarette use was reported by only 4.2 percent of high school students and 1.0 percent of middle school students, representing less than one-third of high school and middle school students reporting any current use [14].

Most current adult users of e-cigarettes have smoked conventional cigarettes [39,41]. Although the prevalence of e-cigarette use among those who currently smoke remained stable from 2014 to 2018, it increased among adults who previously smoked. As an example, in a NHIS survey of young adults who previously smoked, current e-cigarette use increased from 10.4 to 36.5 percent from 2014 to 2018 [30]. Similarly, current e-cigarette use among all adults who previously smoked increased from 4.2 to 5.5 percent [29] from 2017 to 2018.

Adults who recently quit smoking are more likely to use e-cigarettes regularly than those who formerly smoked [45].

In contrast, e-cigarette use is uncommon among adults who have never smoked cigarettes. As an example, among adults who had never smoked cigarettes, only 6.5 percent had ever used e-cigarettes and 1.1 percent currently used them [39]. Similarly, in the United Kingdom in 2015, an estimated 1.7 percent of those who had never smoked were current e-cigarette users [46]. However, among United States young adults, current e-cigarette use in those who never smoked increased from 2014 to 2018 (from 1.5 to 4.6 percent) [30].

Studies indicate that most e-cigarette users perceive these products to be a tool to quit conventional cigarettes or to reduce their risk of tobacco-related disease [41,47,48]. For example, in a survey of 2501 United States adults who smoke, there was a greater interest in using e-cigarettes for the purpose of smoking cessation or reduction than for novelty or to cope with smoking restrictions [49].

ADVERSE HEALTH EFFECTS — Potential adverse effects of e-cigarettes are related to exposure to nicotine as well as to other aerosol components produced by the devices and risks of the actual device.

Nicotine exposure — Nicotine exposure from e-cigarette use, as with cigarette smoking, increases heart rate and produces measurable levels of blood cotinine, a nicotine metabolite [50]. (See "Cardiovascular effects of nicotine", section on 'Smoking and cardiovascular risk'.)

The amount of nicotine delivered and the level of nicotine in the blood varies depending on nicotine concentration in the e-cigarette liquid, other components in the e-cigarette liquid, user experience, puffing intensity, device characteristics, and vaping technique [51]. Experienced e-cigarette users tend to take longer puffs and use the device more intensively compared with novice users [52]. As a consequence, they have higher blood nicotine levels that more closely resemble the levels achieved by smoking conventional cigarettes [1,50,53-55]. In less-experienced users, however, the nicotine delivered by e-cigarettes is consistently lower than nicotine delivered by conventional cigarettes [56,57].

Data on the health consequences of chronic nicotine exposure alone in the absence of cigarette smoking are available from studies of chronic users of nicotine replacement products. These data do not suggest that chronic nicotine exposure increases long-term cardiopulmonary or cancer risk. (See "Cardiovascular effects of nicotine", section on 'Safety of nicotine replacement therapy'.)

Aerosol (also known as vapor) exposure — Commercially manufactured e-cigarettes do not expose the user to many of the constituents of cigarette smoke (eg, tars, oxidant gases, and carbon monoxide) that are responsible for many of the tobacco-attributable diseases [58]. However, most manufactured e-cigarettes do contain a number of potentially toxic chemical substances [1]. Furthermore, people may refill empty e-cigarette cartridges with various substances and carriers that may increase risk of harm when heated for inhalation.

In 2019, the Centers for Disease Control and Prevention (CDC) reported over two thousand suspected cases of severe lung illnesses (e-cigarette, or vaping, product use associated lung injury [EVALI]) linked to the use of e-cigarette devices to aerosolize substances for inhalation [59-64]. In the majority of cases, tetrahydrocannabinol (THC) had been inhaled within three months of symptom onset; many patients had also inhaled nicotine, and some patients had inhaled only nicotine [62]. Refilled e-cigarette cartridges obtained via informal or illicit sources and contaminated with vitamin E acetate appear to be most strongly associated with EVALI cases, and vitamin E acetate has been detected in bronchoalveolar lavage fluid samples obtained from affected patients [60,61,65]. EVALI is discussed in greater detail elsewhere. (See "E-cigarette or vaping product use-associated lung injury (EVALI)".)

E-cigarette use has also been associated with the development of acute eosinophilic pneumonia. (See "Idiopathic acute eosinophilic pneumonia", section on 'Etiology'.)

Prior to the emergence of EVALI, most experts believed that inhaling e-cigarette aerosol was less likely to be harmful (acutely or chronically) than inhaling cigarette smoke [1,2,66]. The consequences of chronic e-cigarette aerosol inhalation are largely unknown, and levels of toxic and carcinogenic compounds may vary depending on the e-cigarette liquid components and device used [67]. Little is known about the overall safety or the carcinogenic effects of propylene glycol or glycerol when heated and aerosolized. At high temperatures, propylene glycol decomposes and may form propylene oxide, a probable human carcinogen [68]. Glycerol produces the toxin acrolein, though the levels produced are lower than conventional cigarettes [15]. Both propylene glycol and glycerol decompose to form the carcinogens formaldehyde and acetaldehyde, with levels depending on the voltage of the battery used in the e-cigarette [67,69].

Other carcinogenic compounds have been found in e-cigarettes, but in trace amounts that are much lower than levels found in conventional cigarettes. These include tobacco-specific nitrosamines (TSNAs), carbonyl compounds, metals, volatile organic compounds (VOCs), and phenolic compounds [1,18,26,27]. A small observational study found that users of e-cigarettes for at least six months (who did not smoke conventional cigarettes) had substantially lower urinary and salivary concentrations of TSNAs and VOCs than did those who smoked conventional cigarettes [54]. It is not known whether the particles in e-cigarette aerosol have any toxicity. (See "Secondhand smoke exposure: Effects in adults" and "Secondhand smoke exposure: Effects in children", section on 'Is exposure to e-cigarette vapor harmful?'.)

The long-term cardiovascular risks of e-cigarette use are unknown but are thought to be substantially lower than the risks of smoking [70]. Aerosol constituents that may influence this risk include nicotine, oxidizing chemicals, particulate matter, and acrolein [71]. A small observational study found that e-cigarette use for at least one year was associated with factors that have been correlated with increased cardiovascular risk: increased oxidative stress and a shift toward sympathetic predominance in cardiac autonomic balance [72]. By contrast, another small study found that, compared with a sham control or non-nicotine e-cigarette, acute exposure to an e-cigarette containing nicotine was not associated with increased oxidative stress but was associated with increased cardiac sympathetic nerve activity [73]. A randomized control trial found that those who switched from conventional to e-cigarettes had improvement in endothelial function and vascular stiffness within one month [74].

The use of nicotine containing e-cigarettes may cause a mild, short-term increase in blood pressure [73,75], although the long-term effects on blood pressure are unclear. (See "Smoking and hypertension", section on 'E-cigarettes and blood pressure'.)

Although limited evidence on the effects of e-cigarette aerosol suggests that changes in airway respiratory function are much smaller than those associated with conventional cigarettes, there may be an association with cough and asthma symptoms, particularly among adolescents [1,6]. In one survey of over 45,000 students (mean age 14.6 years) in Hong Kong, e-cigarette use was associated with respiratory symptoms (cough or phlegm), regardless of cigarette smoking status [76]. Similarly, in a survey of 11th- and 12th-grade students in California, there was an association between self-reported chronic bronchitic symptoms (chronic cough, phlegm, or bronchitis within the past year) and current or past e-cigarette use that remained after adjustment for cigarette smoking or secondhand smoke exposure; the risk increased with frequency of current e-cigarette use [77]. Among adults, there is some evidence of an association between e-cigarette use and respiratory symptoms, although the risk appears to be lower than that with cigarette smoking [78,79].

The effect of inhaling flavorings on respiratory function is also uncertain [80]. Some studies have found a link between cytotoxicity and certain flavorings used in e-cigarette liquids, especially sweet and cinnamon flavors [81-85]. Specifically, diacetyl, a chemical associated with respiratory diseases, has been found in sweet-flavored e-cigarettes [86]. Cherry-flavored e-cigarettes have been found to contain benzaldehyde, a compound that has been associated with respiratory irritation [87].

No observational data examining the long-term risk of cancer from e-cigarettes exist; however, the risk of cancer is likely to be much lower in adults who use e-cigarettes than in those who smoke conventional cigarettes [1,70,88].

Risks of devices — E-cigarette devices have been reported to cause burns, explosive injuries, and chemical injuries [70,89-92].

Several reviews have identified emergency department visits for burns from electronic nicotine delivery systems (ENDS) due to device malfunction either while stored (eg, in a pocket) or during use, resulting in burns to the thigh, groin, face, and/or hand [92,93].

In addition, exposure to e-cigarette liquid via oral or parenteral ingestion, or through skin contact, can also cause harm, particularly to young children. Such exposure may commonly cause nausea, vomiting, lethargy, and tachycardia and may even result in seizures, anoxic brain injury, lactic acidosis, and death. (See "Nicotine poisoning (e-cigarettes, tobacco products, plants, and pesticides)".)

CONCERNS RELATED TO YOUTH AND NONSMOKERS — For adolescents and others who are not established cigarette smokers, the primary focus is on the potential risks of e-cigarette use. Non-smokers are not using e-cigarettes to help them stop using conventional cigarettes, so there is no mitigating harm-reduction. Concerns about the risks of e-cigarettes are accentuated by the rapidly increasing prevalence of e-cigarette use among youth in the United States (figure 3 and figure 4), with many adolescents reporting very frequent use, including during the school day. (See 'Prevalence' above.)

Specific concerns about e-cigarette use by youth include:

Nicotine dependence – Use of e-cigarettes raises the risk of establishing nicotine dependence in novice users, which could ultimately lead to combustible tobacco use. This potential gateway effect is suggested by observations that e-cigarette use often precedes conventional cigarette use [94-99]. As examples:

A systematic review and meta-analysis of longitudinal studies among 17,389 adolescents and young adults aged 14 to 30 years showed that, compared with e-cigarette never users, ever users had a higher probability of initiating cigarette smoking (31 versus 8 percent, pooled adjusted odds ratio [OR] 3.50 [95% CI, 2.38-5.16]) [97,100].

In a prospective study of ninth-grade students, an association was seen between use of e-cigarettes and other forms of tobacco and use of conventional cigarettes. After adjusting for other risk factors for smoking, baseline e-cigarette use was associated with a greater likelihood of using any combustible tobacco product (OR 2.7, 95% CI 2.0-3.7), including conventional cigarettes (OR 2.7, 95% CI 1.7-4.0), cigars (OR 4.9, 95% CI 3.4-7.0), and hookahs (OR 3.3, 95% CI 2.3-4.6) [94].

Some of these findings may be related to the association between the predisposition of an adolescent or young adult to smoke conventional cigarettes and their predisposition to smoke e-cigarettes. However, analysis of psychosocial risk factors suggests that many youth who use e-cigarettes are unlikely to have initiated tobacco smoking with cigarettes [101].

Adverse effects – E-cigarette use raises the risk of adverse effects (eg, respiratory symptoms), some of which have been reported particularly among youth [76,77,102]. (See 'Aerosol (also known as vapor) exposure' above and "E-cigarette or vaping product use-associated lung injury (EVALI)".)

In addition, one internet survey of adolescents and young adults found that dual use of cigarettes and e-cigarettes may be associated with an increased risk of self-reported infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the agent that causes COVID-19 [103].

Normalizing smoking behavior – E-cigarette use may normalize smoking behavior, which might contribute to conventional cigarette use. (See 'Renormalization of smoking behavior' below.)

The long-term effects of nicotine exposure through e-cigarette use only, including the effects of e-cigarette use during pregnancy, are not known. (See "Cigarette and tobacco products in pregnancy: Impact on pregnancy and the neonate".)

Given the concerns that e-cigarette use may be a gateway to nicotine dependence among adolescents, many public health authorities have recommended restricting e-cigarette marketing and advertising to youth and banning flavorings, similar to strategies used to reduce tobacco use by youth [104-107]. (See 'Regulatory status' below and "Prevention of smoking and vaping initiation in children and adolescents", section on 'Advertising and media influence'.)

There is ample evidence that e-cigarettes have been marketed using many of the strategies previously used by tobacco companies to market conventional cigarettes to youth [108]. For example, e-cigarettes have been commonly marketed with flavorings, which appeal to youths and are banned in conventional cigarettes for this reason [22,109]. Exposure to e-cigarette marketing has been associated with e-cigarette use among youth and young adults [110,111].

These issues are discussed in more detail separately. (See "Prevention of smoking and vaping initiation in children and adolescents", section on 'Vaping nicotine'.)

ROLE IN SMOKING CESSATION — The available clinical trial evidence suggests that e-cigarettes may be effective as smoking cessation aids, but more trials are needed to fully evaluate the safety and efficacy of e-cigarettes for smoking cessation [1,7,112,113]. E-cigarettes may be more attractive to users than other medications for smoking cessation because they look and taste more like conventional cigarettes and permit the user to continue the hand-to-mouth ritual of smoking [114]. In small studies, users of e-cigarettes reported reduced conventional cigarette cravings and nicotine withdrawal symptoms [50,53]. However, there is the theoretical concern that e-cigarettes could deter people from using smoking cessation medications with a known record of safety and efficacy [58]. The American Thoracic Society recommends using proven pharmacotherapy (ie, varenicline) rather than e-cigarettes for smoking cessation, and the US Preventive Services Task Force concludes that the evidence is insufficient to fully evaluate the benefits and harms of e-cigarettes for smoking cessation [112,115]. This is reviewed in detail elsewhere. (See "Pharmacotherapy for smoking cessation in adults".)

Some people who have stopped using conventional cigarettes (and therefore are considered to have quit) may or may not continue to use e-cigarettes [116]. However, discontinuing both conventional cigarettes and e-cigarettes is advisable in order to avoid whatever longer-term risk may be associated with e-cigarettes alone. The nature and magnitude of these risks are uncertain at this time.

Efficacy — There is increasing evidence from randomized clinical trials that e-cigarettes are effective for smoking cessation, although the long-term effectiveness and safety of e-cigarettes compared with available pharmacotherapies is uncertain based upon limited high-quality data [1,7,70,113]. In addition, most trials used earlier e-cigarette products, which may limit the generalizability of trial results; newer e-cigarette devices allow for a higher nicotine dose delivery, and these products may be more effective for smoking cessation than earlier devices [117]. Further randomized trials, specifically using later e-cigarette devices, are needed.

In published studies:

In a randomized trial including almost 900 people who smoked combustible tobacco cigarettes in the United Kingdom, e-cigarettes were more effective in smoking cessation than nicotine replacement therapy (NRT) at one year [116]. Participants were provided either an e-cigarette starter pack or nicotine replacement products of their choice for three months; all users were provided at least four weekly behavioral support sessions. Biochemically proven cigarette abstinence rates at one year were 18.0 percent in the e-cigarette user group and 9.9 percent in the NRT group (relative risk [RR] 1.83; 95% CI 1.20-2.58). Among those who were abstinent from cigarettes at one year, 80 percent of those in the e-cigarette group were still using e-cigarettes, compared with 9 percent of those in the NRT group who continued to use NRT. At one year, those in the e-cigarette group had greater declines in the incidence of cough and phlegm production compared with those in the NRT group. The safety of sustained e-cigarette use after quitting conventional cigarette smoking represents harm reduction, although whether long-term e-cigarette use among those who formerly smoked conventional cigarettes has any negative long-term health consequences is not yet known.

In a randomized trial, approximately 375 Canadian adults who smoked conventional cigarettes were assigned to receive nicotine e-cigarettes, non-nicotine e-cigarettes, or no e-cigarettes for 12 weeks; all groups received counseling [7]. At 12 weeks, self-reported smoking abstinence (point prevalence) was greater among those receiving nicotine e-cigarettes plus counseling compared with counseling alone (22 versus 9 percent); the difference became nonsignificant by 24 weeks. Interpretation of the trial results, however, is limited by methodologic issues, including early termination and underpowering to detect study group differences.

In another randomized trial including over 650 adults who smoked conventional cigarettes in New Zealand, participants were randomly assigned to nicotine-containing (16 mg) e-cigarettes, nicotine-free e-cigarettes, or 21 mg nicotine patches [118]. At six months, the biochemically verified smoking cessation rates were modest among all groups (7 versus 4 versus 6 percent, respectively), and did not differ significantly. Observed quit rates were lower than in most clinical trials, suggesting the study may have had selection bias or other methodologic issues.

In a 2021 systematic review including 61 trials (of which 34 were randomized controlled trials) and over 16,000 participants, there was moderate-certainty evidence that, among those who smoke conventional cigarettes, quit rates were higher with the use of nicotine e-cigarettes compared with NRT (RR 1.53, 95% CI 1.21-1.93), and that quit rates were higher with the use of nicotine e-cigarettes compared with non-nicotine e-cigarettes (RR 1.94, 95% CI 1.21-23.13); the certainty of all evidence was limited by imprecision [113].

Observational trials provide evidence on how these devices are being used in actual practice rather than in clinical trials. Results from observational studies are mixed [119-128]. Some studies suggest an association between e-cigarette use and smoking cessation or reduction [129]. However, multiple earlier studies have suggested that e-cigarette use is not associated with higher rates of quitting or reducing smoking [119,123,130,131].

Smoking reduction — An individual will gain the most benefit if smoking is stopped entirely. However, e-cigarettes might have the potential to reduce harm from tobacco-related diseases by replacing or reducing conventional cigarette use [132-134]. There is little evidence to support this hypothesis, and the degree to which smoking reduction must be achieved is not established.

Replacing conventional cigarettes – The primary benefit hypothesized is a reduction in the negative health consequences of conventional cigarette use for those who switch completely to e-cigarettes. This could decrease conventional smoking rates at the population level and should lead to a reduction in tobacco-attributable morbidity and mortality. Theoretically, the reduction in tobacco-attributed morbidity and mortality could be offset by any long-term adverse effects of e-cigarettes. (See 'Adverse health effects' above.)

Dual use – If e-cigarettes lead to dual use (with conventional cigarettes), the individual might still reduce their tobacco-attributable risk of chronic disease if they reduce the number of conventional cigarettes smoked. However, the relationship between the amount of conventional cigarette smoking and disease is not strictly linear for all conditions. For example, small amounts of smoke exposure can still increase risk for coronary artery disease [135]. (See "Cigarette smoking and other possible risk factors for lung cancer", section on 'Smoking reduction' and "Benefits and consequences of smoking cessation", section on 'Questionable utility of smoking reduction'.)

PUBLIC HEALTH CONCERNS — In 2019, cases of e-cigarette or vaping product use associated lung injury (EVALI) were reported. After epidemiologic investigation, evidence linked these cases primarily to vaping tetrahydrocannabinol (THC) products that had been contaminated with vitamin E acetate rather than to the use of commercially sold nicotine-containing e-cigarettes. (See "E-cigarette or vaping product use-associated lung injury (EVALI)".)

Other potential impacts of e-cigarettes on public health include concerns include e-cigarettes' appeal to youth, their potential to reverse gains in social norms about the acceptability of cigarette smoking ("renormalization"), and the risk of dependence [1,136]. However, dependence appears to be lower than for conventional tobacco cigarettes [1].

In addition, there have been increasing reports of poisoning in children related to e-cigarettes and concerns about the possible effects of secondhand exposure to the aerosol. A US Surgeon General’s report about the risks of e-cigarettes to youth highlights the importance of preventing the initiation of nicotine use by adolescents [105].

Renormalization of smoking behavior — If e-cigarettes are allowed where cigarette smoking is not, they could reverse the "de-normalization" of smoking behavior brought about by the spread of smoke-free laws [2,137]. These laws are credited with contributing to reducing smoking prevalence in the United States. Tobacco smoking could be "renormalized" and the public health gains rolled back [138]. In theory, this might discourage the frequency and success of quit attempts, encourage relapse among those who previously smoked, and increase tobacco use initiation rates among youth and young adults. At present, there is no evidence of smoking renormalization.

Nicotine poisoning — E-cigarette fluid contains highly concentrated liquid nicotine. Exploratory ingestions in young children and intentional ingestions in adolescents and adults have been associated with life-threatening toxicity and death. The clinical manifestations and initial management of nicotine poisoning are provided in a rapid overview (table 1) and discussed in detail separately. (See "Nicotine poisoning (e-cigarettes, tobacco products, plants, and pesticides)".)

Secondhand aerosol exposure — There are concerns about the potential health consequences of secondhand exposure to e-cigarette aerosol due to increases in environmental concentrations of nicotine and particulate matter [1]. However, passive exposure to e-cigarette aerosol is expected to be less toxic to bystanders than conventional cigarette smoke [1,139,140]. Aerosol released from e-cigarettes will depend on user technique, temperature, e-cigarette device, and other factors [141].

There is limited evidence on the health effects of passive e-cigarette aerosol exposure. Passive exposure to aerosol produces small increases in serum cotinine, comparable with that from passive exposure to cigarette smoke [142]. (See 'Aerosol (also known as vapor) exposure' above.)

REGULATORY STATUS — Regulation of e-cigarettes varies by country and is continually evolving. Multiple organizations have recommended more government regulation [104,106,143-146]. They have called for regulation that would treat e-cigarettes like conventional cigarettes, banning their use where conventional cigarettes are banned and subjecting e-cigarettes' content, sales, and marketing to regulatory constraints similar to those that apply to conventional cigarettes. Some have suggested that taxation for e-cigarettes should be lower than for conventional cigarettes to encourage adults who smoke conventional cigarettes to switch to e-cigarettes for harm reduction [147].

Worldwide — The World Health Organization (WHO) report on e-cigarettes suggested that regulations were needed to stop promotion of e-cigarettes to nonsmokers and young people, minimize potential health risks to users and nonusers, stop unproven health claims about e-cigarettes, and protect existing tobacco control efforts [143]. While the WHO acknowledged that additional research on e-cigarettes was needed, it also emphasized the need to restrict e-cigarette advertising and indoor use. Some groups have disagreed with the WHO report, suggesting that the risks of e-cigarettes were overstated [148,149].

United Kingdom — In the United Kingdom, the Royal College of Physicians Tobacco Advisory Group recommended a balanced regulatory approach that ensures product safety while enabling and encouraging those who smoke to use e-cigarettes instead of tobacco to reduce harm to health [150]. The report suggests that while e-cigarettes are not harmless, they are likely less harmful than conventional cigarettes [151].

United States — The US Food and Drug Administration (FDA) does not regulate e-cigarettes as medical products through the Center for Drug Evaluation and Policy (CDER), which regulates nicotine replacement products such as nicotine patches. E-cigarette manufacturers could apply to CDER for approval to market the devices as smoking cessation aids, but no manufacturer has yet done so.

Instead, the FDA regulates e-cigarettes through its Center for Tobacco Products (CTP). Initially, the 2009 Family Smoking Prevention and Tobacco Control Act granted the CTP the authority to regulate cigarettes and smokeless tobacco but not other tobacco products, including cigars and e-cigarettes [152]. In 2016, the regulation was amended to include any product "made or derived from tobacco that is intended for human consumption," including e-cigarettes that contain nicotine but not e-cigarettes that are nicotine-free [153].

FDA regulations require that e-cigarette manufacturers demonstrate that their products meet the FDA standard of providing a net public health benefit or face the possibility of being removed from the market [154]. The FDA voluntarily delayed enforcement of this standard while it developed a process for conducting these evaluations. It required manufacturers to submit an application for approval of e-cigarette products by September, 2020 [154]. In September 2021, the FDA announced that it had acted on over 90 percent of applications, issuing denials to over 900,000 flavored products due to health concerns related to their popularity among youth [155]. Subsequently, in October 2021, the FDA for the first time authorized the marketing of some electronic nicotine delivery system (ENDS) products, while noting that this ruling “does not mean these products are safe or ‘FDA approved’” [156].

The FDA also requires manufacturers, and in many cases retailers ("vape shops") where e-cigarette devices are modified and sold, to disclose the ingredients in their products and demonstrate that they are safe [157,158].

The FDA prohibits the sale of tobacco and e-cigarette products to those aged <21 years, sales in vending machines (except in adult-only venues), and distribution of free samples [159]. In addition, there are federal regulations to minimize the risk of exposure of youth to e-cigarettes, including prohibition of sales of flavored liquids (other than menthol or tobacco) in devices that use pre-filled cartridges [160,161]. Flavored e-cigarette liquids, however, are available for sale in vape shops for use in devices that have refillable tanks. In addition, this ban did not apply to flavored disposable e-cigarettes, which have become increasingly popular among youth. Among high school e-cigarette users, for example, the percentage who reported using disposable e-cigarettes increased from 2.4 percent in 2019 to 26.5 percent in 2020 [14]. The FDA has attempted to remove these flavored disposable e-cigarettes from the market but, despite this effort, many remain on the market [162,163].

A number of states and many municipalities have banned the use of e-cigarettes in areas where cigarette smoking is also completely banned (with limited exceptions in a few states), and additional states and municipalities have banned e-cigarette use in other venues [164]. E-cigarette use is also banned on airplanes [165].

Other countries — E-cigarettes have been banned in some countries [58]. In Europe, the European Parliament approved a directive that regulates nicotine-containing e-cigarettes with concentrations up to 20 mg/mL as tobacco products [166]. E-cigarettes with higher nicotine concentrations are regulated as medical devices. The directive includes regulation for the maximum amount of nicotine in e-cigarette liquids and requires child tamper-proof packaging.

COUNSELING FOR PATIENTS — In the absence of clear outcomes data on the health consequences of e-cigarette use and their efficacy for smoking cessation, evidence-based definitive recommendations cannot be made [167].

Information for counseling patients on what is known related to e-cigarettes is available from some medical societies’ documents on e-cigarettes. Policy statements from the American Cancer Society, American Heart Association, and other groups provide guidance on addressing e-cigarette use in clinical practice [144,145,168-170]. The Centers for Disease Control and Prevention (CDC) also provides guidance to clinicians and the public about electronic cigarettes [171].

For children, a report by the Surgeon General, “Know the risks, e-cigarettes and young people,” includes information sheets that clinicians may use to educate patients as well as a tip sheet for parents [105]. Information for adolescents and their caregivers about e-cigarettes is available from the CDC website, including content about health risks and other frequently asked questions and advice for caregivers on how to keep kids e-cigarette-free [172].

Given the available evidence, we discuss these points with patients in a conversation about e-cigarettes:

Recreational use of e-cigarettes should not be initiated; non-smokers should not start using or use e-cigarettes [173].

For those who smoke combustible tobacco products, a complete switch to using nicotine-containing e-cigarettes is likely to be less harmful, but the health risks of long-term e-cigarette use are not yet known. Therefore, those who switch to e-cigarettes should eventually plan to quit e-cigarette use as well, so long as that does not lead to relapse (ie, smoking combustible cigarettes). Dual use of combustible cigarettes and e-cigarettes is not likely to substantially reduce the risk of tobacco-related disease.

E-cigarette or vaping product use associated lung injury (EVALI) has been associated with vaping of tetrahydrocannabinol (THC) products contaminated by vitamin E acetate rather than commercially purchased nicotine-containing e-cigarettes. E-cigarette products should not be bought “off the street,” adulterated, or altered (ie, should not have any substances added to the commercially manufactured product) [60]. (See "E-cigarette or vaping product use-associated lung injury (EVALI)".)

For those who smoke conventional cigarettes who are interested in using e-cigarettes for smoking cessation, we also discuss the following:

No e-cigarette has been approved by the US Food and Drug Administration (FDA) for smoking cessation, and the FDA has not endorsed their safety or efficacy for smoking cessation.

People should be congratulated on their interest in smoking cessation and reminded that safe and effective treatments to help them reach that goal already exist.

Individuals should be encouraged to try the FDA-approved products first because of the lack of evidence regarding the practical effectiveness of e-cigarettes in promoting smoking cessation. Those who previously failed conventional treatments should be assessed for proper medication use and/or consider second-line therapies. (See "Pharmacotherapy for smoking cessation in adults".)

If individuals are unwilling to use FDA-approved medications for smoking cessation, it is up to the clinician's judgment whether to support the use of e-cigarettes. Smokers should be made aware of the uncertainty about their safety and efficacy as therapeutic devices. People who choose to use e-cigarettes to quit should be advised to switch completely to e-cigarettes and use them regularly as substitutes for tobacco cigarettes, rather than using e-cigarettes while continuing to smoke tobacco cigarettes.

Regardless of the method chosen, it is important for the individual to understand that their efforts to become smoke-free will continue to receive the clinician's strongest support and assistance.

The use of e-cigarettes should not be permitted in hospitals or health care facilities. Conventional cigarettes are not allowed in these venues. Nicotine replacement products, not e-cigarettes, should be used to manage nicotine withdrawal symptoms in hospitalized patients. (See "Pharmacotherapy for smoking cessation in adults", section on 'Nicotine replacement therapy' and "Pharmacotherapy for smoking cessation in adults", section on 'Hospitalized patients'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Smoking cessation, e-cigarettes, and tobacco control".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

Basics topics (see "Patient education: Vaping (The Basics)")

SUMMARY AND RECOMMENDATIONS

E-cigarette devices and liquids – Electronic cigarettes (e-cigarettes) are electronic devices that usually deliver nicotine; they consist of a cartridge containing a liquid, an atomizer (vaporization chamber with a heating element), and a battery. The user activates the atomizer, which heats the liquid and produces an aerosol (sometimes referred to as a vapor) to inhale (figure 1 and figure 2). Across all brands, the main components in nicotine e-cigarette liquids are nicotine, propylene glycol or glycerol, and flavorings. A variety of other compounds have also been identified. (See 'Electronic nicotine delivery systems' above.)

Prevalence and patterns of use – The use of e-cigarettes by adults has increased over the past decade, and while it had more significantly increased among middle and high school students, the prevalence of use among youth appears to be declining. Most adult e-cigarette users also currently smoke conventional tobacco cigarettes. A majority of e-cigarette users perceive them to be a tool to quit or reduce their smoking. (See 'Prevalence and patterns of use' above.)

Adverse health effects – Potential adverse effects of e-cigarettes are related to exposure to nicotine as well as to other aerosol components produced by the devices and risks of the actual device. No observational data examining the long-term risk of cancer from e-cigarettes exist; however, the risk is likely to be much lower in adults who use e-cigarettes than in those who smoke conventional cigarettes. (See 'Adverse health effects' above.)

In 2019, the Centers for Disease Control and Prevention (CDC) reported over two thousand cases of severe acute lung illnesses (e-cigarette, or vaping, product use associated lung injury [EVALI]) linked to the use of e-cigarette devices to aerosolize substances for inhalation. Vitamin E acetate has been linked to EVALI, although the exact cause has yet to be determined. (See 'Aerosol (also known as vapor) exposure' above and "E-cigarette or vaping product use-associated lung injury (EVALI)".)

Role of e-cigarettes in smoking cessation – For adults, the evidence that e-cigarettes are effective smoking cessation aids is growing, but the risks remain uncertain. Clinicians should encourage adults who inquire about quitting smoking to use smoking cessation aids approved by the US Food and Drug Administration (FDA), including pharmacotherapy as a first choice. For adults who have quit smoking but are using e-cigarettes, clinicians should strongly advise them not to return to smoking cigarettes but might consider offering nicotine replacement products as alternatives if the individual wishes to stop using e-cigarettes. (See 'Role in smoking cessation' above and 'Counseling for patients' above.)

Public health concerns – Public health concerns regarding e-cigarettes include EVALI as well as the potential to increase youth initiation of tobacco products (figure 3 and figure 4), renormalize tobacco use in places where cigarette smoking is not acceptable, and lead to nicotine dependence. Accidental nicotine poisoning in children has been reported. The health effects of secondhand aerosol exposure are unknown. (See 'Concerns related to youth and nonsmokers' above and 'Public health concerns' above.)

Patient counseling – Recreational use of e-cigarettes should not be initiated; non-smokers should not start using or use e-cigarettes. E-cigarette products should not be bought "off the street," adulterated, or altered (ie, should not have any substances added to the commercially manufactured product). (See 'Counseling for patients' above.)

ACKNOWLEDGMENT — The UpToDate editorial staff acknowledges Stephen Rennard, MD, and Sara Kalkhoran, MD, MAS, who contributed to an earlier version of this topic review.

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Topic 98400 Version 83.0

References

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