Table 1

Study characteristics related to design of study, setting, number of participants, mean age, gender, inclusion and exclusion criteria, and follow-up.

Author, yearDesign of studyLocationNo.* participantsMean ageNo. male (%)Inclusion criteriaExclusion criteriaFollow-up (months)
Randomized controlled trials
Adriaens, 201430Parallel
Leuven, Belgium50ENDS1: 44.7
ENDS2: 46.0
ENDS and e-liquid**: 40.3
21 (43.7)Being a smoker for at least three years; smoking a minimum of 10 factory-made cigarettes per day and not having the intention to quit smoking in the near future, but willing to try out a less unhealthy alternativeSelf-reported diabetes; severe allergies; asthma or other respiratory diseases; psychiatric problems; dependence on chemicals other than nicotine, pregnancy; breast feeding; high blood pressure; cardiovascular disease; currently using any kind of smoking cessation therapy and prior use of an e-cigarette8
Bullen, 201331–36Parallel
New Zealand65716 mg ENDS: 43.6
21 mg patches NRT: 40.4
ENNDS: 43.2
252 (38.3)Aged 18 years or older; had smoked ten or more cigarettes per day for the past year; wanted to stop smoking; and could provide consentPregnant and breastfeeding women; people using cessation drugs or in an existing cessation programme; those reporting heart attack, stroke, or severe angina in the previous two weeks; and those with poorly controlled medical disorders, allergies, or other chemical dependence6
Caponnetto, 201325Parallel
Catania, Italy3007.2 mg ENDS: 45.9
7.2 mg ENDS+5.4 mg ENDS: 43.9
ENNDS: 42.2
190 (63.3)Smoke 10 factory made cigarettes per day (cig/day) for at least the past five years; age 18–70 years; in good general health; not currently attempting to quit smoking or wishing to do so in the next 30 days; committed to follow the trial proceduresSymptomatic cardiovascular disease; symptomatic respiratory disease; regular psychotropic medication use; current or past history of alcohol abuse; use of smokeless tobacco or nicotine replacement therapy, and pregnancy or breastfeeding12
Cohort studies
Al-Delaimy, 201537CohortCalifornia, US628Not reported478 (47.8)Residents of California; aged 18 to 59 years who had smoked at least 100 cigarettes during their lifetime and are current smokersParticipants who reported that they “might use e-cig” or changed their reporting at follow-up, as they did not represent a definitive group of users or never-users e-cig and might overlap with both12
Biener, 201538CohortDallas and Indianapolis areas, US1374Not reported383 (55.2)Adults smokers residing in the Dallas and Indianapolis metropolitan areas, who had been interviewed by telephone and gave permission to be re-contactedAnyone over 65 years old36
Brose, 201540–42CohortWeb-based, United Kingdom3891***ENDS
Among daily users: 45.7
Among non-daily users: 45.2
No ENDSα: 45.7
2,015 (49.6)Members were invited by e-mail to participate in an online study about smoking and who answered a screening question about their past-year smoking statusBaseline pipe or cigar smokers, and follow-up pipe or cigar smokers or unsure about smoking status12
Hajek 201546CohortEurope100ENDS: 41.8
No ENDS: 39
57 (57)All smokers joining the UK Stop Smoking Services in addition to the standard treatment (weekly support and stop smoking medications including NRT and varenicline).No exclusion criteria4 weeksβ
Harrington 201546CohortUS97946.0****525 (53.6)Hospitalized cigarette smokers at a tertiary care medical center; self-identified smoker who smoked at least one puff in previous 30 days; English speaking and reading; over age 18 and; cognitively and physically able to participate in studyPregnant6
Manzoli, 201543CohortAbruzzo and Lazio region, Italy1355ENDS only:
Tobacco cigarettes only: 44.2
Dual smoking: 44.3
757 (55.9)Aged between 30 and 75 years; smoker of e-cig (inhaling at least 50 puffs per week) containing nicotine since six or more months (E-cig only group); smoker of at least one traditional cigarette per day since six or more months (traditional cigarettes only group); smoker of both electronic and traditional cigarettes (at least one per day) since six or more months (mixed Group)Illicit drug use, breastfeeding or pregnancy, major depression or other psychiatric conditions, severe allergies, active antihypertensive medication, angina pectoris, past episodes of major cardiovascular diseases (myocardial infarction, stroke/TIA, congestive heart failure, COPD, cancer of the lung, esophagus, larynx, oral cavity, bladder, pancreas, kidney, stomach, cervix, and myeloid leukemia12
Borderud, 201439CohortNew York, US1074ENDS use+ behavioral and pharmacological treatment: 56.3
No ENDS+behavioral and pharmacological treatment: 55.6
467 (43.5)Patients with cancer referred to a tobacco cessation program who provided data on their recent (past 30 days) e-cig useNo exclusion criteria6 to 12
Prochaska 201444CohortUS95639.0****478
Adult daily smokers (at least 5 cigarettes/day with serious mental illness at four psychiatric hospitals in the San Francisco Bay AreaNon-English speaking; medical contraindications to NRT use (pregnancy, recent myocardial infarction); and lack of capacity to consent as determined by a 3-item screener of study purpose, risks, and benefits18
Vickerman 201345CohortUS2,758Used ENDS one month or more: 48.1
Used ENDS less than one month: 45.3
No ENDS: 49.6
913 (36.9)Participants from six state quitlines who registered for tobacco cessation services. Adult tobacco users, consented to evaluation follow-up, spoke English, provided a valid phone number, and completed at least one intervention callNo exclusion criteria7
  • no.: number; e-cig: e-cigarettes; ENDS: Electronic nicotine delivery system; ENNDS: electronic non-nicotine delivery systems; RCT: randomized controlled trial; US: United States; ENDS1 and ENDS2: the e-cig groups received the e-cig and four bottles of e-liquid at session 1 (group e-cig1 received the “Joyetech eGo-C” and group e-cig2 received the “Kanger T2-CC”); at session 2, participants' empty bottles were replenished up to again four bottles and at session 3, they were allowed to keep the remaining bottles.

  • *Randomized or at baseline

  • **For the first two months control group consisted of no e-cigarettes use. After that period, the participants of control group received the e-cig and e-liquid. ENDS1=“Joyetech eGo-C” e-cig and ENDS2=“Kanger T2-CC” e-cig.

  • ***The 4117 were reported in a publication that focused on baseline characteristics, not on the use of e-cigarettes and changes in smoking behavior, so the remaining 53 participants are irrelevant to this review.

  • ****Mean age of the overall population.

  • αThe comparator comprises of current non-users of e-cig, which included never-users and those who had previously tried but were not using at the moment.

  • βHajek 2015 was the only study that entered in the review due to meet the criteria for adverse events.

  • But only 2,476 asnwered the question “Have you ever used e-cigarettes, electronic, or vapor cigarettes?”