TABLE 1.

Characteristics of included studies

Authors (year) [ref.]	Design	Country	Number of participants	Eligibility criteria	Participants’ characteristics	Interventions	Main outcome
Bonevski et al. (2021) [ 14 ]	RCT: two parallel groups	New Zealand	Total n=100: 50 EC, 50 NRT	≥18 years old; tobacco smokers and with capacity to provide informed consent	67% women, mean age 41 years, smoking 21 (mean) cpd	Randomised to nicotine EC and NRT for 12 weeks	Self-reported 6-week continuous abstinence at 12 weeks (not validated)
Bullen et al. (2013) [ 17 ]	RCT: three parallel groups	Australia	Total n=100: 289 nicotine EC, 295 patch, 73 non-nicotine EC (this group was not included in this review)	≥18 years old; smoked ≥10 cpd over past year, and wanted to stop smoking	62% women, mean age 42 years, smoking 18 (mean) cpd	Randomised to nicotine EC, NRT, and non-nicotine EC for 12 weeks	Continuous abstinence 6 months after quit day (biochemically validated)
Hajek et al. (2019) [ 18 ]	RCT: two parallel groups	UK	Total n=100: 439 EC, 447 NRT	≥18 years old; with no strong preference to EC and NRT, and were currently not using either type of product	48% women; median age 41 years, smoking 15 (median) cpd	Randomised to nicotine EC and NRT (for at least 4 weeks and up to 3 months)	Continuous abstinence 52 weeks after quit day (biochemically validated)
Lee et al. (2018) [ 20 ]	RCT: two parallel groups	USA	Total n=100: 20 EC, 30 NRT	≥18 years old; currently smoked ≥2 cpd and at least once in the last 7 days	10% women; mean age 54 years, smoking 14 (mean) cpd	Randomised to nicotine EC (6-week supply) and NRT (5 weeks nicotine patch, 1 week placebo match)	7-day point prevalence abstinence at 6 months (biochemically validated)

cpd: cigarettes per day; EC: e-cigarette; NRT: nicotine replacement therapy; RCT: randomised controlled trial.