Smith 2020.

Study characteristics
Methods	Design: Double‐blind randomized controlled trial Recruitment: Recruited from the local area via advertising on craigslist social media Setting: Laboratory and electronic diaries, USA Study start date/Study end date: Not specified.
Participants	Total N: 30 N per arm: PG/VG ratio 70/30 = NR; PG/VG ratio 50/50 = NR; PG/VG ratio 0/100 = NR Inclusion criteria: adults age ≥ 18 who have been smoking at least 5 cigarettes daily for the past year (expired CO > 8) usual brand is non‐menthol use of ENDS on 5 or fewer lifetime occasions regular use of e‐mail or smartphone ownership with capacity to receive SMS text and internet access (necessary for electronic diaries) Exclusion criteria: unwilling to use ENDS as part of the trial use of smokeless, hookah, or tobacco products other than cigarettes ≥ 10 days in the past 30 days pregnant, trying to become pregnant, or breastfeeding recent history of cardiovascular distress in the last 3 months (arrhythmia, heart attack, stroke, uncontrolled hypertension) current use of cessation medications another household member currently enrolled in the study (to prevent contamination of e‐liquid assignment during sampling) 30% women; mean age 43.7; mean cpd 18.5; mean FTND 5.4 Motivated to quit: Not specified E‐cigarette use at baseline: Participants had used an e‐cigarette an average of 1.6 times in their life, and no one reported use in the last 30 days
Interventions	EC: Cig‐a‐like EC provided for 1 week. All aspects of the ENDS device and e‐liquid were held constant between groups with the exception of PG/VG ratio: PG/VG ratio 70/30; PG/VG ratio 50/50; PG/VG ratio 0/100. Ego‐T 1100 mAh battery and disposable cartomizers (510 Smoketech, 1.5‐Ω dual coil). E‐liquid was tobacco‐flavored (Classic Tobacco, American E‐liquid) and contained 18 mg nicotine/ml
Outcomes	1 week; 2 lab visits pre and post and participant diaries Adverse events and biomarkers: Participants provided a CO sample at each visit Other outcomes measured: cpd, ENDS puffs
Study funding	Funding for this project was provided by pilot funding from the National Cancer Institute (P01CA200512 to K.M.C.). Salary support provided by the National Institute on Drug Abuse (K12DA031794 to T.T.S., K23DA041616 to B.W.H.)
Author declarations	M.J.C. has received consulting honoraria from Pfizer. K.M.C. has received payment as a consultant to Pfizer, Inc., for service on an external advisory panel to assess ways to improve smoking cessation delivery in health care settings. He also has served as paid expert witness in litigation filed against the tobacco industry
Notes	Additional data provided from authors. New for 2020 update.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: “At the conclusion of the lab visit, participants were randomized and assigned to take home one of the three e‐liquids to use at home for a 1‐week sampling period (10 participants/ratio).” Quote: “Participants were randomly assigned to receive one e‐liquid to take home for 1 week.” (no further detail given)
Allocation concealment (selection bias)	Unclear risk	Not specified
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Quote: “PG/VG ratio was blinded from participant and staff members who conducted experimental sessions.”
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Biochemical validation
Incomplete outcome data (attrition bias) All outcomes	Low risk	Number of participants at follow‐up not reported, but this may be due to the 1‐week follow‐up and it seems that all participants (excluding 1 participant who was not randomized) were followed up
Selective reporting (reporting bias)	Unclear risk	No protocol. Few details for CO measurements, just percentage change for each group, but mean CO data provided by author on request