The study will shed light on the behavioral effects of: 1) varying e-cigarette nicotine content, known to be important in maintaining conventional cigarette use; and 2) varying e-cigarette non-nicotine tobacco alkaloid (NNTA) content, about which little is known regarding the role in product use or dependence. The study will assess the effects of e-cigarette nicotine and NNTA content on cigarette smokers who will be randomized to conditions that manipulate the nicotine and NNTA content of e-cigarettes.