Procedures

The overall study included four study visits: 1) baseline visit, where precessation metrics were collected, 2) A brief check-in visit 1 week after the baseline visit to assess compliance, 3) An e-cigarette visit 2 weeks after the baseline visit after the transition to transdermal NRT and nicotine-free e-cigarette use, and 4) a follow-up visit approximately 1 month after the e-cigarette visit to assess smoking behavior. The baseline and e-cigarette visits followed the same general timeline. The 2-week duration between the baseline and e-cigarette visits was chosen to allow for the transition to e-cigarettes. This duration also was chosen to prevent potential habituation to the cue reactivity task. Previous work has shown that cue exposure repeatedly evokes craving even with a shorter, 1-week duration between cue presentations (15).

Before the baseline study visit, participants were instructed to smoke as usual. Expired carbon monoxide (CO) was measured at the beginning of each study visit to provide a biochemical measure of smoking behavior. To standardize the duration between the last cigarette smoked and all procedures, participants smoked one of their own cigarettes (baseline visit) approximately 1 h before the cue exposure task. Craving was evaluated before and after cue exposure. After cue exposure, withdrawal was measured by the Wisconsin Smoking Withdrawal Scale [WSWS (16)] (∼3.5 h after smoking).

At the end of the baseline visit, participants were provided transdermal NRT adjusted to their reported quantity of cigarette use (14 mg or 21 mg) and instructed in how to use this product. Participants also received nicotine-free e-cigarettes. The Apollo Challenger brand e-cigarettes (https://www.apolloecigs.com/en/e-cigarette-vape-kits/cigalikes-disposables/apollo-challenger-kit) were used, which are cigarette-like in appearance and were used in conjunction with the tobacco or menthol flavored e-liquid (matched to the participant’s typical use) containing 0 mg nicotine. Participants were instructed to discontinue using their tobacco cigarettes at this time and were only to use the provided e-cigarettes, but they could use them as frequently as they liked. Participants were told that the amount of nicotine in both the e-cigarette and NRT combined was roughly equivalent to the amount they received in their typical smoking pattern, but that there was the possibility that the e-cigarette could contain no-nicotine. All participants received 0 mg e-cigarettes and were debriefed at the end of the study. To equate the study day timelines on the baseline and e-cigarette visits, participants used one of their e-cigarettes for 15 min approximately 1 h before the cue reactivity task. Between the baseline and e-cigarette visits, participants were asked to fill out daily diaries to document their use of e-cigarettes, NRT, and tobacco cigarette.