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. …