The purpose of this study is to estimate nicotine uptake and assess subjective effects during ad libitum use sessions of 4 flavors of JUUL ENDS (also referred to as nicotine salt pod system; NSPS) products (i.e., Virginia Tobacco, Mint, Menthol and Mango) with 2 different nicotine concentrations. Subjective effects will also be assessed to gain an understanding of the user's experience during and after JUUL ENDS product use to evaluate the abuse liability of the products. The subject population will consist of healthy adult, male and female smokers, 21 to 65 years of age.