Cigarette Harm Reduction With Electronic Cigarette Use

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 * \- Body Mass Index ≤ 38.0 * \- Expired Carbon Dioxide (CO) \>=5ppm * Current regular "dual" user of both electronic cigarette (EC) and tobacco cigarette (TC) * EC device use at least 10 or more days in the past 30 days * Daily use of conventional TC (at least 10 cigarettes per day (CPD), as confirmed by saliva cotinine \>50 ng/ml and/or NicAlert=6) * Age: \>= 21 years old to \<= 70 years old * Willingness to use a non-menthol e-cigarette only (until menthol flavored SREC becomes available) * Willingness to abstain from marijuana for the duration of the study Exclusion Criteria: * Unstable medical conditions (such as unstable heart disease, seizures, cancer, uncontrolled thyroid disease, diabetes, Hepatitis B or C or renal or liver impairment, glaucoma, history of stroke, an ulcer in the past year, or active use of an inhaler for Asthma or Chronic obstructive pulmonary disease (COPD). * Psychiatric conditions (such as current or past schizophrenia and/or current or past bipolar disorder, major personality disorder, or major depression current or within the past year. Participants with current or past minor to moderate depression and/or anxiety disorders will be reviewed by the study physician and considered for inclusion. Psychiatric hospitalizations are not exclusionary, but study participation will be determined as per study physician's approval. * Psychiatric medications with the exception of Selective Serotonin Reuptake Inhibitors (SSRI) and Serotonin and norepinephrine reuptake inhibitors (SNRIs) and current evaluation by the study physician that the participant is otherwise healthy, stable and able to participate. * Pregnancy or breastfeeding (by history and pregnancy test); women of childbearing potential must be using an acceptable method of contraception * 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 \[no more than 15 times in combination in the past month and must agree to abstain from their use during the period of the study.\] * Concurrent use of nicotine-containing medications * 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 at the screening visit (THC ok). Must not be on opioid replacement therapy. * Medications: Use of medications that are inducers of nicotine metabolizing enzyme CYP2A6 (Example: rifampicin, dexamethasone, phenobarbital, and other anticonvulsant drugs). Use of medications for cardiovascular conditions including hypertension (Example: beta- and alpha-blocking drugs). Use of stimulants (Example: Adderall) * Other/Misc Health Conditions: Oral thrush; fainting within the last 30 days; untreated thyroid disease; other "life threatening illnesses" as per study physician's discretion. * 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