Study characteristics related to population, intervention or exposure groups, comparator, and assessed outcomes.
| Author, year | Population | No.* of participants intend to quit smoking | No.* of participants in intervention or exposure groups and comparator | Description of intervention or exposure groups | Description of comparators | Measured outcomes | Definition of quitters or abstinence |
|---|---|---|---|---|---|---|---|
| Randomized controlled trials | |||||||
| Adriaens, 201433 | Participants unwilling to quit smoking (participants from the control group kept on smoking regular tobacco cigarettes during the first eight weeks of the study) | Yes 0 No 50 | ENDS 1: 16 ENDS 2: 17 Control/ENDS: 17 | ENDS (“Joyetech eGo-C”) ENDS E-cigarettes (“Kanger T2-CC”) | ENDS and e-liquid** | Quitting, defined as eCO of 5 ppm or smaller; questionnaire self-report of reduction in cigarettes of>50% or complete quitting | No more cigarette smoking |
| Bullen, 201334–39 | Had smoked ten or more cigarettes per day for the past year, interested in quitting | Yes 657 No 0 | ENDS: 289 NRT: 295 ENNDS: 73 | 16 mg nicotine ENDS | 21 mg patches NRT ENNDS | Continuous smoking abstinence, biochemically verified (eCO measurement <10 ppm); seven day point prevalence abstinence; reduction; and adverse events | Abstinence allowing ≤5 cigarettes in total, and proportion reporting no smoking of tobacco cigarettes, not a puff, in the past 7 days |
| Caponnetto, 201325 | Smokers not intending to quit | Yes 0 No 300 | ENDS 1: 100 ENDS 2: 100 ENNDS: 100 | 7.2 mg nicotine ENDS 7.2 mg nicotine ENDS+5.4 mg nicotine ENDS | ENNDS | Self-report of reduction in cigarettes of>50%; abstinence from smoking, defined as complete self-reported abstinence from tobacco smoking - not even a puff, biochemically verified (eCO measurement ≤7 ppm); and adverse events | Complete self-reported abstinence from tobacco smoking - not even a puff |
| Cohort studies | |||||||
| Al-Delaimy, 201540 | Current smokers; regardless of whether the users were using ENDS as part of a quit attempt | Yes 415 No 542 | ENDS: 236Ψ No ENDS: 392Ψ | ENDS | No ENDS | Quit attempts; 20% reduction in monthly no. of cigarettes; and current abstinence from cigarette use | Duration of abstinence of one month or longer to be currently abstinent |
| Biener, 201529 | All respondents had reported being cigarette smokers at baseline; regardless of whether the users were using ENDS as part of a quit attempt | Yes 364β No 331€ | 1374$ | ENDS£ intermittent use ENDS£ intensive use | No ENDS (used once or twice ENDS) | Smoking cessation; and reduction in motivation to quit smoking among those who had not quit, not otherwise specified | Smoking cessation was defined as abstinence from cigarettes for at least one month |
| Brose, 201526–28 | Current smokers; regardless of whether the users were using ENDS as part of a quit attempt | Not reported | ENDS: 1507 No ENDS: 2610 | ENDS daily ENDS non-daily | No ENDS€ | Quit attemptsφ; cessationϖ; and substantial reduction defined as a reduction by at least 50% from baseline CPD to follow-up CPD | Change from being a smoker at baseline to being an ex-smoker at follow-up was coded as cessation |
| Hajek, 201546 | 69% (n=69) accepted e-cigs as part of their smoking cessation treatment | Not reported | ENDS: 69 No ENDS: 31 | ENDS was offered to all smokers in addition to the standard treatment (weekly support and stop smoking medications including NRT and varenicline) | No ENDS | Self-reported abstinence was biochemically validated by exhaled CO levels in end-expired breath using a cut-off point on 9ppm, adverse events | Self-reported abstinence from cigarettes at 4 weeks |
| Harrington, 201545 | Hospitalized cigarette smokers. All were cigarette smokers initially; regardless of whether the users were using ENDS as part of a quit attempt | Yes: 220*** No: not reported | ENDS: 171 No ENDS: 759 | ENDS | No ENDS | Quitting smoking based on 30-day point prevalence at 6 months | Only self-reported quitting smoking |
| Manzoli, 201542 | Smokers of ≥1 tobacco cigarette/day (tobacco smokers), users of any type of e-cig, inhaling ≥50 puffs weekly (e-smokers), or smokers of both tobacco and e-cig (dual smokers) | Not reported | ENDS: 343 Tobacco and ENDS: 319 Tobacco only: 693 | ENDS Tobacco and ENDS | Tobacco cigarettes only | Abstinence, proportion of quitters, biochemically verified (eCO measurement>7ppm), reduce tobacco smoking, and serious adverse events | Percentage of subjects reporting sustained (30 days) smoking abstinence from tobacco smoking |
| Borderud, 201441 | Patients who presented for cancer treatment and identified as current smokers (any tobacco use within the past 30 days); regardless of whether the users were using ENDS as part of a quit attempt | Yes 633¥ No 42¥ | ENDS: 285 No ENDS: 789 | ENDS£+Evidence-based behavioral and pharmacologic treatment | No ENDS+Evidence-based behavioral and pharmacologic treatment | Smoking cessation by self-report | Patients were asked if they had smoked even a puff of a (traditional) cigarette within the last 7 days |
| Prochaska, 201443 | Adult daily smokers with serious mental illness; regardless of whether the users were using ENDS as part of a quit attempt | At baseline, 24% intended to quit smoking in the next month | ENDS: 101 No ENDS: 855 | ENDS | No ENDS | Smoking cessation by self-report and, biochemically verified (CO and cotinine) | Past 7 day tobacco abstinence |
| Vickerman, 201344 | Adult tobacco current or past users; regardless of whether the users were using ENDS as part of a quit attempt | Not reported | ENDS: 765 No ENDS: 1,711 | ENDS used for 1 month or more ENDS used for less than 1 month | No ENDS (never tried) | Tobacco abstinence | Self-reported 30-day tobacco abstinence at 7 month follow-up |
no.: number; C: comparator group; CPD: cigarettes smoked per day; e-cig: e-cigarettes; ENDS: Electronic nicotine delivery system; ENNDS: electronic non-nicotine delivery systems; eCO: exhaled breath carbon monoxide; NE: non-exposure group; NRT: Nicotine replacement therapy.
*Numbers 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.
***Only among those who reported any previous use of e-cigs.
αInformation retrieved through contact with author.
€The 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.
ΨParticipants who will never use e-cig plus those who never heard of e-cig=392; participants who have used e-cig=236 (numbers taken from the California Smokers Cohort, a longitudinal survey).
βIntentions to quit smoking, those who tried e-cigarettes only once or twice are grouped with never users (“non-users/triers”).
€Intermittent use (i.e., used regularly, but not daily for more than 1 month) plus intensive use (i.e., used e-cig daily for at least 1 month).
$No. of the whole sample including comparator.
£All ENDS.
¥The other participants either quit more than a month ago but less than six months, less than a month ago, or more than six months ago.
φSmokers and recent ex-smokers were asked about the number of attempts to stop they had made in the previous year. Those reporting at least one attempt and 37 respondents who did not report an attempt but had stopped smoking be- tween baseline and follow-up were coded as having made an attempt.
ϖChange from being a smoker at baseline to being an ex-smoker at follow-up was coded as cessation.