Are ENDS effective for smoking cessation?
The evidence for ENDS as aids to smoking cessation remains murky (Table 118-22). There is a paucity of randomized controlled clinical trials (RCTs) investigating ENDS for smoking cessation or reduction, and it is difficult to quantify the amount of nicotine used in ENDS because of the variety of delivery systems and cartridges. In a recent Cochrane review, those using ENDS to quit smoking were more likely to be abstinent from combustible cigarettes at 6 months vs those using nicotine-free ENDS (relative risk = 2.29; 95% CI, 1.05 to 4.96), but there was no significant difference in quit rates compared with nicotine patches.23 However, the confidence in this finding was rated as low because of the limited number of RCTs. Of note, the authors found 15 ongoing RCTs at the time of publication that might be eligible for later evaluation.
Non-RCTs reveal mixed data. Positive results include 1 study with an odds ratio of 6.07 to quit for intensive ENDS users vs non-users,24 and another with dual users of combustible and electronic cigarettes having a 46% quit rate at 1 year.25 Additionally, in a pilot study providing ENDS to 14 patients with schizophrenia who had no previous desire to quit smoking, authors noted a reduction in the number of cigarettes smoked per day by 50% in one-half of participants and abstinence in 14% of participants at 52 weeks.26 Studies with neutral or negative results include those showing ENDS users to be current combustible tobacco smokers, and use of ENDS not predicting smoking cessation.4,27 Data also are mixed regarding the use of ENDS as a harm reduction strategy. One study found that ENDS decreased cigarette consumption, but did not increase the likelihood of quitting,28 while another reported that daily use of ENDS increased the odds of reducing smoking by as much as 2.5 times compared with non-use of such aids.29 In a 24-month prospective cohort study following tobacco users, there was no difference in the number of cigarettes smoked per day in those who started the trial as users of combustible cigarettes alone vs combustible cigarettes plus ENDS users.30 Interestingly, those who started the study as combustible cigarette users and switched to ENDS and those who had continued dual use throughout the 24 months smoked fewer combustible cigarettes per day than those who never tried ENDS or quit during the study period.
Health effects
To better understand the adverse health effects of ENDS, one must consider potential short- and long-term consequences (Table 2). In the short-term, ENDS have been found to increase markers of inflammation and oxidative stress acutely as evidenced by in vivo laboratory studies.31,32 ENDS also have been linked to upper respiratory irritation, in part, because of the transformation of glycerin in the nicotine cartridge to acrolein upon combustion.33 Even 5 minutes of ad lib E-cig use has been found to significantly increase airflow resistance during pulmonary function tests34—changes that have been shown to precede more persistent alterations in peak expiratory flow, such as those seen in chronic obstructive pulmonary disease. The more common patient-reported side effects include:
- daytime cough (27%)
- phlegm production (25%)
- headache (21%)
- dry mouth/throat (20%)
- vertigo, headache, or nausea (9%).35,36
A RCT investigating efficacy of E-cigs vs nicotine patches vs denicotinized E-cigs found no difference among the groups in the number of reported adverse events.18 Interestingly, another RCT found a decrease in adverse events, such as dry cough, mouth irritation, throat irritation, shortness of breath, and headache, compared with baseline in combustible cigarette smokers who used regular or denicotinized E-cigs.19
Although no studies have directly investigated long-term health consequences of ENDS because of their relative novelty, one can extrapolate potential harmful long-term effects based on knowledge of the products’ chemical constituents. For example, propylene glycol can degrade into propylene oxide, a class 2B carcinogen.37 Other potential carcinogens in the aerosol include formaldehyde and acetaldehyde. On a broader scale, many of the particulates have been shown to cause systemic inflammation, which is thought to increase cardiovascular and respiratory disease and death.38 Flavorings in ENDS include a variety of components including, but not limited to, aldehydes, which are irritants, and other additives that have been associated with respiratory disease.39
Second-hand exposure. There are no long-term studies of second-hand vapor exposure, but similar to long-term health on primary users, one can glean some observations from the literature. It is promising that compared with cigarettes, ENDS lack sidestream smoke and the vapor has not been found to contain carbon monoxide.40 Some research has demonstrated that the size and spray of fine particles in the aerosol is as large or larger than combustible cigarettes.41 Formaldehyde, acetaldehyde, isoprene, and acetic acid have been found in ENDS vapor.40 Interestingly, a simulated café study found elevated nicotine, glycerine, hydrocarbon, and other materials classified as carcinogens in the air.42
Although it is popularly thought that ENDS are less toxic than tobacco cigarettes, there is not enough evidence to estimate precisely as to how much less toxic or the consequences of use. ENDS are increasingly popular and are being used by never smokers who should be educated on the potential harm that ENDS pose.