Table 1.

Characteristics of included studies.

Authors	Study design	Duration of intervention: follow up (weeks)	Population (N)	Intervention (N)	Control (N)	Outcomes	Results
Caponnetto et al. ECLAT study (21) Italy	RCT 3 arms: 2 intervention groups and 1 control group	12: 52	300 smokers Not intend to quit	1st generation - E cig Arbi Group®, ad libitum use, 12 weeks at 7.2 mg (100) - E cig Arbi Group®, ad libitum use, 6 weeks 7.2 mg then 6 weeks 5.4 mg (100)	E cig 0 mg (100)	- Abstinence at 12months (since previous visit at 6 months, confirmed with CO < 7 ppm) - Reduction: CPD decrease ≥50% of initial - AE at each study visits	- Significant abstinence in nicotine group at week 12 and 52 vs E cig 0 mg - No statistical difference for smoking reduction - No serious AE reported
Cobb et al. (23)	RCT 4 arms: 2 intervention groups and 2 control group	24:36	520 smokers Not intend to quit	2nd generation - E cig EGO 8mg - E cig EGO 36 mg	- Cigarette substitute - - E cig 0 mg	−7DPP and 28 day or more abstinence with CO < 10 ppm - Reduction: CPD decrease - AE	- Significantly more participants in the 36 mg/ml group than in the 0 mg/ml group are abstinent at 24 weeks - Significant decrease of CPD over times - Serious AE frequency similar across groups, not related to product use
Bullen et al. ASCEND study (22) New Zealand	RCT 3 arms: 2 intervention groups and 1 control group	12: 24	657 smokers Intend to quit	1st generation E cig 16 mg Elusion® (289)	- Nicotine patch 21 mg (295) - - E cig 0 mg (73)	- Continuous abstinence (≤ 5 cigarettes allowed) with CO < 10 ppm - Reduction: CPD decrease ≥50% of initial - AE	- No significant difference between nicotine e cig vs patches and vs 0 mg for abstinence - Significant decrease of CPD at 24 weeks - No serious AE classified as being related to product use
Eisenberg et al. (25) Canada	RCT 3 arms: 1 intervention group and 2 control groups	12: 52	376 smokers Intend to quit	2nd generation E cig 15 mg NJOY® (128)	- E cig 0 mg (127) - Counseling (121)	- 7 day PP abstinence - Continuous abstinence with CO < 10 ppm - Reduction: CPD decrease - AE at each study visits	- No significant differences in abstinence between nicotine and non-nicotine e-cigarettes groups at 12 weeks or 24 weeks - Significant decrease of CPD at 24 weeks - No serious AE
Hajek et al. (28) UK	RCT 2 arms: 1 intervention groups and 1 control group	12 (4 first weeks with behavioral support): 52	884 smokers Intend to quit	2nd generation E cig 18 mg Aspire® (438)	Nicotine replacement group: choice among the range of nicotine replacement products (patch, gum,...) (446)	- Continuous abstinence (≤ 5 cigarettes allowed) with CO < 8 ppm - AE at each study visits	- Significantly more abstinence in the E cig 18mg group than in the NRT group - No serious AE classified as being related to product use
Lee et al. (26) Korea	RCT 2 arms: 1 intervention group and 1 control group	12: 52	150 smokers Intend to quit	2nd generation E cig eGO-c ovale® 0,01 mg/mL (75)	Nicotine gum 2 mg (75)	- Continuous abstinence with CO < 10 ppm + 7 day PP abstinence at 12 and 24 weeks - Smoking reduction - AE	- No significant statistical difference at 12 and 24 weeks for abstinence - Smoking reduction was higher in the nicotine e cigarette group than NRT group - No serious AE reported
Lucchiari et al. (27) Italy	RCT 2 arms: 1 intervention group and 1 control group	12: 52	210 smokers Intend to quit	2nd generation E cig 8 mg (70)	- E cig 0 mg (70) - Counseling (70)	- Continuous abstinence with CO < 7 ppm - Reduction: CPD decrease - AE	- No significant statistical difference after 24 weeks for abstinence - Significant effect of group E cig 8 mg on CPD: after 24 weeks, participants in the nicotine e-cigarette group smoked fewer cigarettes than any other group. - No serious AE reported

RCT, randomized controlled trial; CPD, cigarettes per day; 7 day PP abstinence, 7 day point prevalence abstinence; AE, Adverse events.