Standardized e-cigarette tested against usual brands in nicotine study

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * Healthy on the basis of medical history and limited physical examination- * Heart rate \< 105 beats per minute (BPM)\*. * Systolic Blood Pressure \< 160 and \> 90\*. * Diastolic Blood Pressure \< 100 and \> 50\*. * \*considered out of range if both machine and manual readings are above/below these thresholds. * Body Mass Index \<= 38.0. * Current regular user of electronic cigarettes (EC) * EC device use at least 15 or more days in the past 30 days (with e- liquid \>= 3mg/ml) * No restriction on flavor or type of e-cigarette used * Saliva cotinine \>= 50 ng/ml and/or NicAlert = 6 * Age \>= 21 years old \<= 70 years old * Willingness to abstain from drug use for the duration of the study Exclusion Criteria: * The following unstable medical conditions: * Heart disease * Seizures * Cancer * Thyroid disease (okay if controlled with medication) * Diabetes * Hepatitis B or C or Liver disease * Glaucoma * Kidney disease or urinary retention * History of stroke * An ulcer in the past year * Active use of an inhaler for Asthma or chronic obstructive pulmonary disease (COPD) * Medications * Use of medications that are inducers of nicotine metabolizing enzyme CYP2A6 (Example: rifampicin, carbamazepine, phenobarbital, and other anticonvulsant drugs). * Use of sympatholytic medications for cardiovascular conditions including hypertension (Example: beta and alpha-blockers). * Concurrent use of nicotine-containing medications (Example: nicotine patch, lozenge, gum). * Any stimulant medications (example: Adderall) generally given for attention deficit hyperactivity disorder (ADHD) treatment. * Other/Misc. Health Conditions * Oral thrush * Fainting (within the last 30 days) * Other "life threatening illnesses" as per principal investigator and/or study physician's discretion * Pregnancy * Pregnancy (self-reported and urine pregnancy test) * Breastfeeding (determined by self-report) * Women of childbearing potential must be using an acceptable method of contraception * Concurrent participation in another clinical trial. * Inability to read and write in English * Planning to quit smoking or vaping within the next 60 days * A known propylene glycol/vegetable glycerin allergy * Uncomfortable with getting blood drawn * Recent onset or change (worsening) in cough, fever and/or abdominal symptoms (vomiting or pain) in the past two weeks