Abstract
INTRODUCTION: Characterizing flavors are widely available in e-cigarettes and motivate initiation and continued use. Flavors may enhance appeal and facilitate development of addiction to tobacco products through modulation of tobacco products' reinforcing or aversive actions. Palatable flavors (eg, fruit) may increase appeal through primary reinforcing properties. Menthol's cooling and anesthetic effects may increase appeal by counteracting nicotine's aversive effects. Genetics provide a method for modeling individual differences in sensitivity to nicotine's effects. A common polymorphism, rs16969968, encoded in the α5 nicotinic acetylcholine receptor subunit gene (CHRNA5), is a well-recognized marker for smoking risk and reduces sensitivity to nicotine aversiveness. METHODS: This pilot study tested how flavors impacted e-cigarette appeal and self-administration. In a single testing day, cigarette smokers (N = 32; 94% menthol-smokers) self-administered e-cigarettes containing e-liquids differing in nicotine level (0 mg/mL, 24 mg/mL) and flavor (unflavored, menthol, fruit-flavored) within directed and ad libitum e-cigarette paradigms. Subjective drug effects, number of puffs, rs16969968 genotype, plasma nicotine, and menthol glucuronide levels were collected. RESULTS: Menthol partially ameliorated nicotine aversiveness; fruit did not. In nicotine's absence, fruit flavor increased self-reported preference and ad libitum use relative to menthol-containing or unflavored e-liquids. Individuals with high-smoking-risk rs16969968 genotype (N = 7) reported greater craving alleviation following directed administration of nicotine-containing e-liquids, showed a trend rating nicotine-containing e-liquids as less harsh, and self-administered more nicotine during ad libitum compared to individuals with low-smoking-risk genotype (N = 23). CONCLUSIONS: While menthol countered aversiveness of nicotine-containing e-liquids, fruit flavor increased appeal of nicotine-free e-liquids. These preliminary findings suggest menthol and fruit flavor increase e-cigarettes' appeal through distinct mechanisms. IMPLICATIONS: This study provides a detailed characterization of the effects of flavors (unflavored, menthol, fruit), nicotine (0 mg/mL, 24 mg/mL) and their interactions on the subjective drug effects and ad libitum self-administration of e-cigarettes. Genetics were used to assess these effects in higher-smoking-risk (diminished sensitivity to nicotine aversiveness) and lower-risk groups. Findings could inform impact of regulation of flavors or nicotine in e-cigarettes, and their impacts on vulnerable sub-populations.