Vaping High vs. Low Nicotine E-Liquid

Inclusion Criteria: * Healthy on the basis of medical history and limited physical examination, as described below: * 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. * Age: \>= 21 years * Age: \<= 70 years * Current regular user of open tank electronic cigarette (EC) (at least 20 times in the past 30 days) with e-liquid nicotine of 3-6 mg/mL. * Non-smoker or non-daily cigarette smokers agreeing to abstain from cigarettes for the duration of the study. * Saliva cotinine \>50 ng/mL and/or NicAlert=6 * Carbon monoxide \>= 5 ppm or per discretion of Principal Investigator Exclusion Criteria: * Medical * 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) * Psychiatric conditions * Current or past schizophrenia, and/or current or past bipolar disorder * Major depression, current or within the past year * Major personality disorder * Participants with current or past minor or moderate depression and/or anxiety disorders will be reviewed by the PI and considered for inclusion * History of psychiatric hospitalizations is not exclusionary, but study participation will be determined as per PI's approval * Drug/Alcohol Dependence * Alcohol or illicit drug dependence within the past 12 months with the exception of those who have recently completed an alcohol/drug treatment program * Positive toxicology test for illicit drugs at the screening visit (THC \& prescribed medications okay) * Opioid replacement therapy (including methadone, buprenorphine, or other) * Psychiatric medications * Current regular use of any psychiatric medications with the exception of Selective Serotonin Reuptake Inhibitors (SSRIs) and serotonin-norepinephrine reuptake Inhibitors (SNRIs) and current evaluation by the PI that the participant is otherwise healthy, stable, and able to participate. * 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 * Any stimulant medications (example: Adderall) generally given for attention deficit hyperactivity disorder (ADHD) treatment * Other/Misc. Chronic Health Conditions * Oral thrush * Fainting (within the last 30 days) * Other "life threatening illnesses" as per PI's discretion * Pregnancy * Pregnancy (self-reported and urine pregnancy test) * Breastfeeding (determined by self-report) * Concurrent participation in another clinical trial * Inability to read and write in English * Planning to quit vaping within the next 60 days * Concurrent regular use of marijuana (occasional users of these products may be enrolled if they agree to abstain from their use during the period of the study) * Use of other tobacco products, smokeless tobacco, pipes, cigars/cigarillos, blunts/spliffs (no more than 10 times in the past month and must agree to abstain from their use during the period of the study)