Inclusion Criteria:  Generally healthy individuals (determined by physical examination). Age of 18-29 years. Is willing to provide informed consent. Is willing to attend the lab as required by the study protocol. ENDS users (defined as using ENDS either daily or occasionally in the past 30 days) Have abstained from ENDS use for 12 hours prior to each session.  Exclusion Criteria:  Report smoking cigarettes regularly (> 5 cigarettes/month in the past year). Report regular use of any other tobacco/nicotine product (e.g., e-cig, pipes, cigars) in the past year. Women who are breast-feeding or test positive for pregnancy (by urinalysis at screening). Individuals with self-reported history of chronic disease or psychiatric conditions. Individuals with history of or active cardiovascular disease, low or high blood pressure, seizures, and regular use of prescription medications (other than vitamins or birth control). Individuals that report THC (marijuana) smoking/vaping. Individuals that report the use of non-commercial (i.e., street) e-cigarette liquid or products Individuals that report current EVALI or COVID-19 related symptoms (i.e., cough, shortness of breath, chest pain, nausea, vomiting, abdominal pain, diarrhea, fever, chills, or weight loss) Individuals that have or have been exposed to COVID-19 in the last 14 days.