title: E-cigarettes and smoking cessation in real-world and clinical settings: a systematic review and meta-analysis.
abstract: BACKGROUND
  Smokers increasingly use e-cigarettes for many reasons, including attempts to quit combustible cigarettes and to use nicotine where smoking is prohibited. We aimed to assess the association between e-cigarette use and cigarette smoking cessation among adult cigarette smokers, irrespective of their motivation for using e-cigarettes.
  
  
  METHODS
  PubMed and Web of Science were searched between April 27, 2015, and June 17, 2015. Data extracted included study location, design, population, definition and prevalence of e-cigarette use, comparison group (if applicable), cigarette consumption, level of nicotine dependence, other confounders, definition of quitting smoking, and odds of quitting smoking. The primary endpoint was cigarette smoking cessation. Odds of smoking cessation among smokers using e-cigarettes compared with smokers not using e-cigarettes were assessed using a random effects meta-analysis. A modification of the ACROBAT-NRSI tool and the Cochrane Risk of Bias Tool were used to assess bias. This meta-analysis is registered with PROSPERO (number CRD42015020382).
  
  
  RESULTS
  38 studies (of 577 studies identified) were included in the systematic review; all 20 studies with control groups (15 cohort studies, three cross-sectional studies, and two clinical trials) were included in random effects meta-analysis and sensitivity analyses. Odds of quitting cigarettes were 28% lower in those who used e-cigarettes compared with those who did not use e-cigarettes (odds ratio [OR] 0·72, 95% CI 0·57-0·91). Association of e-cigarette use with quitting did not significantly differ among studies of all smokers using e-cigarettes (irrespective of interest in quitting cigarettes) compared with studies of only smokers interested in cigarette cessation (OR 0·63, 95% CI 0·45-0·86 vs 0·86, 0·60-1·23; p=0·94). Other study characteristics (design, population, comparison group, control variables, time of exposure assessment, biochemical verification of abstinence, and definition of e-cigarette use) were also not associated with the overall effect size (p≥0·77 in all cases).
  
  
  CONCLUSIONS
  As currently being used, e-cigarettes are associated with significantly less quitting among smokers.
  
  
  BACKGROUND
  National Institutes of Health, National Cancer Institute, FDA Center for Tobacco Products.
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, CA, USA.
authors.forename: Sara
authors.initials: S
authors.lastname: Kalkhoran
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, CA, USA; Center for Tobacco Control Research and Education, Cardiovascular Research Institute, University of California San Francisco, San Francisco, CA, USA. Electronic address: glantz@medicine.ucsf.edu.
authors.forename: Stanton A
authors.initials: SA
authors.lastname: Glantz
mesh_terms: D066300:Electronic Nicotine Delivery Systems / Q000706:statistics & numerical data*; D006801:Humans; D009042:Motivation; D016017:Odds Ratio; D015995:Prevalence; D012907:Smoking / Q000453:epidemiology* / Q000628:therapy; D016540:Smoking Cessation / Q000706:statistics & numerical data*