Assisting Smokers to Switch to an e-Cigarette by Accelerating Learning of Adaptive Habits Using D-cycloserine

Inclusion Criteria: 1. Has signed the informed consent form (ICF) and is able to understand the information provided in the ICF. 2. Is 22 to 65 years of age (inclusive) at screening. 3. Smokes ≥ 10 commercially available CCs per day (no brand restrictions), for the last 12 months. 4. Expired air CO reading of at least 10 ppm as assessed at the screening session. 5. Interested in switching to an electronic cigarette. 6. Willing and able to comply with the requirements of the study. 7. Owns a smart phone with text message and data capabilities compatible with necessary surveys. Exclusion Criteria: 1. Is unhealthy or cannot participate in the study for any reason (e.g., medical, psychiatric, and/or social reason) as judged by the Investigator or designated medical staff based on all available assessments from the screening period (e.g., safety laboratory, vital signs, physical examination, ECG, concomitant medications and medical history). 2. Patient Health Questionnaire (PHQ-9) score greater than 9, or a score greater than 0 on item #9 ("Thoughts that you would be better off dead, or of hurting yourself in some way") at screening. 3. Planned use of an FDA-approved smoking cessation product during the study. 4. High Blood Pressure (systolic \>150 mm Hg, diastolic \>95 mm Hg) at screening. 5. Body mass index (BMI) less than 15.0 kg/m2 or greater than 40.0 kg/m2. 6. Coronary heart disease, structural cardiac disease (including, but not limited to valvular heart disease or cardiac murmurs), cardiac dysrhythmias, syncope, cardiac chest pain, or history of heart attack or heart failure. 7. Has received psychotherapy or behavioral treatments within 30 days of screening, or during the study. 8. Taking antidepressants or psychoactive medications (e.g., antipsychotics, antidepressants, benzodiazepines, hypnotics). 9. Use of any of these products in the past 30 days: 1. Illegal drugs (or if the urine drug screen is positive for cocaine, tetrahydrocannabinol (THC), amphetamines, methamphetamines, or opiates); 2. Experimental (investigational) drugs that are unknown to participant; 3. Chronic opiate use; 4. Medications to treat tuberculosis (e.g., isoniazid, ethionamide). 10. Use of smokeless tobacco (chewing tobacco, snuff), cigars (except for "Black \& Mild" cigars or Cigarillos), pipes, hookah, e-cigarettes, nicotine replacement therapy or other smoking cessation treatments within 14 days of screening. 11. Pregnant or nursing (by self-report) or positive pregnancy test.