A systematic review and meta-analysis of the association between e-cigarette use and cigarette abstinence or changes in continued cigarette smoking among individuals who smoke cigarettes

AIMS: With recent marked increase in e-cigarette use, potential associations between e-cigarette use and combustible cigarette smoking are an important public health issue. Following AMSTAR 2 and PRISMA guidelines, this evidence synthesis identified and characterized associations between e-cigarette use and abstinence from/quitting smoking cigarettes and changes in cigarette smoking quantity/frequency. METHODS: The protocol was registered on November 06, 2018 (PROSPERO 2018 CRD42018115674). Three databases (MEDLINE, EMBASE, and PsycINFO) and gray literature were queried from January 01, 2007 to August 20, 2022. Search terms using medical subject headings (MeSH) and general terms were applied to identify studies related to the associations between e-cigarette use among combustible cigarette users and cessation from cigarette smoking. There was no age restriction applied to the population of interest which included individuals who use e-cigarettes (intervention) and individuals who do not use e-cigarettes (control). A priori abstinence outcome measures included: abstinence from/quitting smoking cigarettes, duration of abstinence from cigarette smoking, number of quit attempts made to abstain from cigarette smoking, age at quit attempt/quitting from cigarette smoking, change in cigarette smoking quantity/frequency, and relapse to smoking cigarettes. Results were screened using the PICOS review method. RESULTS: Two meta-analyses comparing e-cigarettes and nicotine replacement therapy (NRT) were non-significant. Findings from three additional meta-analyses comparing nicotine-containing e-cigarettes with behavioral support found significant associations between e-cigarettes and cigarette smoking abstinence at the longest follow-up duration (RR = 2.73, 95% CI 1.15-6.50), 6-month (RR = 2.70, 95% CI 1.39-5.23), and 3-month (RR = 3.49, 95% CI 1.71-7.12) follow-up. Further meta-analyses examining the change in cigarette smoking quantity/frequency was significantly associated with e-cigarette use and a reduction in the number of cigarettes smoked per day (CPD) at the longest follow-up (MD = 4.27, 95% CI 3.02-5.53), and at the 6-month (MD = 4.70, 95% CI 3.34-6.07), 3-month (MD = 4.14, 95% CI 1.11-7.17), 2-month (MD = 4.62, 95% CI 0.01-9.22), and 1-month (MD = 5.44, 95% CI 0.74-10.14) follow-up. CONCLUSIONS: Evidence suggests that the use of nicotine-containing e-cigarettes supports cigarette smoking cessation and reduction among individuals who smoke cigarettes regularly. Further studies are required to see if these patterns hold past the 1-year time point.