The effects of nicotine stimulus and response expectancies on male and female smokers' responses to nicotine-free electronic cigarettes

Background: Electronic cigarettes (e-cigarettes) have been reported to reduce tobacco craving and withdrawal; however, the mechanisms underlying these effects have not been elucidated. Methods: This study examined the contributions of nicotine stimulus and response expectancies to responses to nicotine-free e-cigarettes in 21 e-cigarette naïve smokers (12 male). Participants completed two randomized experimental sessions in which they administered a nicotine-free e-cigarette. During one session they were informed that the e-cigarette contained nicotine and during the other session they were informed that the e-cigarette was nicotine-free. Participants completed subjective assessments before and immediately after sampling ten puffs from the e-cigarette and were then invited to earn additional puffs using a computerized progressive ratio task. Prior to their enrolment in the study, participants provided an estimate of the relative importance of the nicotine content of e-cigarettes for craving relief. Results: Instructions that the e-cigarette contained nicotine were found to reduce both intention to smoke (p. =. 0.017) and withdrawal-related (p. =. 0.018) craving, regardless of a-priori reported beliefs regarding the relative importance of nicotine. Nicotine content instructions were also found to be associated with a shorter latency to self-administration (p. =. 0.005); however, a Sex. ×. Instructions. ×. Response Expectancy interaction (p. =. 0.008) revealed that this effect was specific to women who had strong a-priori nicotine content craving relief expectations. Neither nicotine content instructions nor response expectancies impacted the number of puffs self-administered. Conclusions: Findings suggest that nicotine content expectations contribute to smokers' responses to e-cigarettes, and that a-priori beliefs about nicotine effects may be especially important in women.