E-cigarette use and combustible tobacco cigarette smoking uptake among non-smokers, including relapse in former smokers: umbrella review, systematic review and meta-analysis

Objective To review and summarise the current evidence on uptake of combustible cigarette smoking following e-cigarette use in non-smokers—including never-smokers, people not currently past smokers—through an umbrella review, systematic meta-analysis. Design Umbrella Data sources PubMed, Scopus, Web Science, PsychINFO (Ovid), Medline (Ovid) Wiley Cochrane Library up to April 2020. Results Of 6225 results, 25 studies non-smokers—never, former smokers—with a baseline measure outcome were included. All found increased risk with exposure, although magnitude varied substantially. Using random-effects model, comparing users versus non-e-cigarette users, among never-smokers at OR for initiation was 3.19 (95% CI 2.44 4.16, I 2 85.7%) non-smokers 3.14 1.93 5.11, 91.0%). Among smokers, relapse higher non-users (OR=2.40, 95% 1.50 3.83, 12.3%). Conclusions Across multiple settings, who e-cigarettes are consistently more likely than those avoiding initiate become smokers. The this varied, average around three times odds. Former smokers using have over twice odds as non-e-cigarettes users. This study is first our knowledge pool data latter topic. PROSPERO registration number CRD42020168596.