Free-Base Nicotine or Nicotine Salt e-Liquids in Current E-Cigarette Smokers, PeloPET Study

Inclusion Criteria: * A current exclusive e-cigarette user (\>= 1 vaping bout per day) for at least the past 6 months (confirmed by NicAlert saliva testing strip) * Between 21-50 years old * Willing to provide informed consent and abstain from all tobacco and nicotine use for at least 12 hours prior to visits 2 and 3 * Willing to participate in 3 laboratory visits * Read and speak English * If utilizing study provided rideshare services, will need to live within 20 miles of Wake Forest University Exclusion Criteria: * Self-reported diagnosis of lung disease including asthma, cystic fibrosis, or chronic obstructive pulmonary disease * Unstable or significant psychiatric conditions (past and stable conditions will be allowed) * History of cardiac event or distress within the past 3 months * Currently pregnant (as indicated by urine pregnancy test at the start of each laboratory visit), planning to become pregnant, or breastfeeding (women only) * Use of other tobacco products (e.g., cigarette, cigar, etc.) \> 5 days in the past month * Currently engaging in a tobacco product cessation attempt