1. Prior to study start, subjects must be current smokers of conventional factory-made cigarettes (eCO >10ppm at screening) who have either tried or are occasional users of e-cigarettes. Subjects must be smoking ≥10 cigarettes per day and must have done so for at least one year. Smoking status will be confirmed with a urinary cotinine level of ≥200ng/ml (determined using NicAlert cotinine test kit) and an exhaled breath CO level of >10ppm (determined using a Smokerlyzer breath CO monitor) at screening, as well as by tobacco use questionnaire.