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INTRODUCTION The aim of this systematic review and meta-analysis was to assess the association between e-cigarette use and subsequent smoking cessation in cohort studies and randomized controlled trials (RCT).

METHODS A systematic literature search was finalized 11 November 2019 using EMBASE, Cochrane Library, Scopus, PubMed Health, NICE evidence search, PROSPERO, CRD, PsycInfo, and PubMed including Medline. Inclusion criteria were: reporting empirical results; longitudinal observational design with a minimum of 3 months of follow-up; including general population samples; and allowing for comparison between users and non-users of e-cigarettes. Studies rated as having high risk of bias were excluded. The procedures described by PRISMA were followed, and the quality of evidence was rated using GRADE.

RESULTS Twenty-eight longitudinal, peer-reviewed publications from 26 cohort studies, and eight publications from seven RCTs assessing the association between e-cigarette use and smoking cessation were included in this review. A randomeffects meta-analysis based on 39147 participants in cohort studies showed a pooled unadjusted odds ratio (OR) for smoking cessation among baseline e-cigarette users compared with baseline non-users of 0.97 (95% CI: 0.67-1.40), while the adjusted OR was 0.90 (95% CI: 0.63-1.27). The pooled odds ratio for smoking cessation in RCTs was 1.78 (95% CI: 1.41-2.25). The evidence for cohort studies was graded as very low and for RCTs as low.

CONCLUSIONS We did not find quality evidence for an association between e-cigarette use and smoking cessation. Although RCTs tended to support a more positive association between e-cigarette use and smoking cessation than the cohort studies, the grading of evidence was consistently low.