Objective A systematic review and meta-analysis to investigate the impact of electronic nicotine delivery systems (ENDS) and/or electronic non-nicotine delivery systems (ENNDS) versus no smoking cessation aid, or alternative smoking cessation aids, in cigarette smokers on long-term tobacco use.
Data sources Searches of MEDLINE, EMBASE, PsycInfo, CINAHL, CENTRAL and Web of Science up to December 2015.
Study selection Randomised controlled trials (RCTs) and prospective cohort studies.
Data extraction Three pairs of reviewers independently screened potentially eligible articles, extracted data from included studies on populations, interventions and outcomes and assessed their risk of bias. We used the Grading of Recommendations Assessment, Development and Evaluation approach to rate overall certainty of the evidence by outcome.
Data synthesis Three randomised trials including 1007 participants and nine cohorts including 13 115 participants proved eligible. Results provided by only two RCTs suggest a possible increase in tobacco smoking cessation with ENDS in comparison with ENNDS (RR 2.03, 95% CI 0.94 to 4.38; p=0.07; I2=0%, risk difference (RD) 64/1000 over 6 to 12 months, low-certainty evidence). Results from cohort studies suggested a possible reduction in quit rates with use of ENDS compared with no use of ENDS (OR 0.74, 95% CI 0.55 to 1.00; p=0.051; I2=56%, very low certainty).
Conclusions There is very limited evidence regarding the impact of ENDS or ENNDS on tobacco smoking cessation, reduction or adverse effects: data from RCTs are of low certainty and observational studies of very low certainty. The limitations of the cohort studies led us to a rating of very low-certainty evidence from which no credible inferences can be drawn. Lack of usefulness with regard to address the question of e-cigarettes' efficacy on smoking reduction and cessation was largely due to poor reporting. This review underlines the need to conduct well-designed trials measuring biochemically validated outcomes and adverse effects.
- electronic cigarettes
- smoking cessation
- systematic review
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Contributors All authors contributed to all aspects of this study, including conducting the literature search, study design, data collection, data analysis, data interpretation and writing of the paper. AUTHORS’ CONTRIBUTIONS GG, RED, WM and EAA conceived the review. DH-A undertook the searches. RED, EAS, HG, AA, YC, MP and VA screened search results. EAS organised the retrieval of papers. RED, EAS, HG, AA, YC, MP and VA screened the retrieved papers against inclusion criteria. RED, EAS, HG, AA, YC, MP and VA appraised quality of papers. RED, EAS, HG, AA, YC, MP and VA extracted data from papers. RED wrote to authors of papers for additional information. RED provided additional data about papers. RED and EAS obtained and screened data on unpublished studies. RED managed the data for the review. RED and EAS contributed in entering data into Review Manager (RevMan). RED, EAS, GHG, WM and EAA contributed in analysing RevMan statistical data. RED, EAS, GHG, WM and EAA interpreted the data. RED, EAS, GG, WM and EAA contributed in making statistical inferences. RED, GHG, WM and EAA wrote the review. RED, EAS, HG, AA, YC, MP, VA, EAA, WM and GH took responsibility for reading and checking the review before submission.
Funding The study is funded by a WHO grant.
Disclaimer The funding agencies played no role in the conduct of the research or preparation of the manuscript.
Competing interests Regina El Dib received a Brazilian Research Council (CNPq) scholarship (CNPq 310953/2015-4).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement No additional data available.
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