Common adverse events of electronic cigarettes compared with traditional nicotine replacement therapies: A systematic review and meta-analysis.

Issues: Established literature suggests that electronic cigarettes (EC) are more effective than traditional nicotine replacement therapies (NRT) as a smoking cessation aid, but the factors that mediate this difference remain poorly understood. We examine how adverse events (AE) associated with EC use relative to NRTs differ, with the view that differences in AEs experienced may drive differences in use and compliance.

Approach: Papers for inclusion were identified via a three-tiered search strategy. Eligible articles involved healthy participants and compared nicotine ECs to non-nicotine ECs or NRTs and reported frequency of AE as an outcome. Random-effects meta-analyses were conducted to compare the likelihood for each of the AEs between nicotine ECs, non-nicotine placebo ECs and NRTs.

Key Findings: A total of 3756 papers were identified, of which 18 were meta-analysed (10 cross-sectional and 8 randomised controlled trials). Meta-analytic results found no significant difference in the rates of reported AEs (i.e., cough, oral irritation, nausea) between nicotine ECs and NRTs, and between nicotine and non-nicotine placebo ECs.

Implications: The variation in the incidence of AEs likely does not explain user preferences of ECs to NRTs. Incidence of common AEs reported because of EC and NRT use did not differ significantly. Future work will need to quantify both the adverse and favourable effects of ECs to understand the experiential mechanisms that drive the high uptake of nicotine ECs relative to established NRTs.

Conclusions: There is inconclusive evidence on the incidence of AEs experience when using ECs compared to NRTs, possibly given the small sample size of studies.