Table 2.

Surveys and studies evaluating cigarette reduction or smoking cessation

Reference	Study design and population	Summary of results	Limitations of study
Etter32	Internet survey of 81 ever-users of e-cigs; 37% dual cigarette and e-cig users	Reasons for e-cig use were to quit smoking (53%), health (49%), cost (26%), freedom to use in smoke-free places (21%), and to avoid disturbing others (20%)	Self-selected sample of internet users
Siegel et al33	Online survey of all first-time purchasers of particular e-cigs over 2-week period; 222 respondents (response rate 4.5%)	Reported six-month point prevalence of smoking abstinence of 31%; 66.8% reported a reduction in cigarette smoking	Low response rate; only 1 brand; self-reported abstinence rate
Etter and Bullen34	Self-selected Internet survey of 3587 visitors to e-cigarette websites; 70% former smokers; Of current smokers 60% responded ‘trying to quit’ and 84% ‘trying to reduce’	Reasons for e-cig use were: less perceived toxicity (84%), to quit smoking or avoid relapsing (77%), tobacco craving (79%), withdrawal symptoms (67%), and decreased cost (57%)	Self-selected sample; respondents may have adjusted answers to justify opinions on cessation or safety
Bullen et al35	40 e-cig-naive smokers randomized to use nicotine-containing e-cig, nicotine-free e-cig, Nicorette nicotine inhaler, or usual cigarette	Smoking desire and withdrawal symptoms were most effectively alleviated after the usual cigarette but the 16 mg e-cig and the Nicorette inhaler had similar results and both of these were more effective than the placebo e-cig	Small sample size; limited to smokers not intending to quit; subjects e-cig naïve
Popova and Ling36	Survey of 1836 current or recently (<2 years) former smokers	Of the smokers, 38% had tried an alternative tobacco product, most commonly e-cigarettes. Use of alternative tobacco products was associated with making a quit attempt but not with successful quitting	Internet survey; all results self-reported; unable to link use of specific product(s) with cessation
Goniewicz et al37	On-line recruiting of Polish e-cig users; 179 of 203 survey completers provided usable data	Self-reported results: 66% had quit smoking; additional 25% reported <5 cigarettes per day (CPD); 82% believed e-cigs ‘not completely safe but better than cigarettes’. 60% believed e-cigs addictive but less than cigarettes.	Internet survey; subjects recruited from on-line groups; not a general population; self-reported results
Polosa et al38	Six-month pilot study of 7.4 mg nicotine e-cigs; 40 subjects not interested in quitting; CC smoking allowed though use of e-cigs encouraged; subjects completed diary	67.5% completed the program. Thirteen of 40 subjects had self-reported 50% reduction in CPD at 24 weeks. Nine subjects (22.5%) self-reported quitting by the end of the study; six of them were still using the e-cigs. eCO measured to verify reduction or abstinence	Small study; no control arm; 32.5% did not come to final follow-up visit; self-reported results; technical difficulty with e-cig (older product)
Polosa et al19	24-month prospective observational continuation of above study; e-cigs not provided after first 6 months but subjects could purchase	23 completed all follow-up visits. At 24 months, >50% reduction in CPD was self-reported in 11 of the 40 participants, with a median decrease from 24 to 4 CPD. Smoking abstinence was self-reported in 5 of 40 participants. eCO measured to verify reduction or abstinence. No serious AEs reported; predominant complaints were mouth and throat irritation and dry cough; withdrawal symptoms uncommon	Same as above; 42.5% failed to attend final follow-up visit; assessment of withdrawal symptoms not rigorous; cannot make direct comparison with other cessation products
Caponnetto et al39	12-month prospective trial; 300 smokers not intending to quit received e-cigs (cartridges contained 7.2 mg, 5.4 mg, or 0 mg nicotine); study product provided for 12 weeks; double-blind, controlled, randomized	75% of the subjects returned at week 12, 70.3% at week 24, and 61% at week 52. No significant changes in heart rate, blood pressure, or weight were found over the study duration. Smokers in all three groups reduced diary (self)-recorded CPD by more than 50%; this was associated with reduction in measured eCO levels and was not related to cartridge nicotine content. The subject-reported abstinence rate at 52 weeks was 8.7%. Of the quitters, 26.9% reported still using e-cigarettes; no significant AEs	Cannot compare with other cessation programs since subjects not intending to quit; self-reported results; 40% did not attend final follow-up visit; technical issues with e-cig (older model product)
Caponnetto et al40	14 smokers with schizophrenia; 52 week follow-up; study product provided for 12 weeks; maximum 4 cartridges/day	Sustained 50% reduction in self-reported CPD (14 to 7). Two of 14 self-reported sustained abstinence at 52 weeks. eCO measured to verify reduction or abstinence. AEs included nausea, throat irritation, headache, and dry cough	Small uncontrolled study; assessment of withdrawal symptoms not rigorous
Bullen et al41	657 adult smokers wanting to quit were given nicotine e-cigs, patch, or placebo e-cigs; product was supplied for 13 weeks; subjects were followed for 6 months	Self-reported abstinence rates at 6 months were 7.3% for nicotine e-cig users, 5.8% for patch users, and 4.1% for placebo e-cig users; eCO measured to verify abstinence; no difference in AEs	Study size not optimal for statistical analysis; more dropouts in patch group; low abstinence rates possibly due to inadequate nicotine replacement
Farsalinos et al42	Personal interviews of 111 former smokers who completely switched to e-cigs for >1 month	81% used e-cig with >15 mg/mL nicotine; few non-serious AEs (cough, throat irritation) Self-reported abstinence verified by blood carboxyhaemoglobin	May not reflect general population; majority male subjects

AE, adverse event; CC, conventional cigarette; eCO, exhaled carbon monoxide; e-cig, electronic cigarette.