Establishing the Effect of Flavor on the Addictive Potential of Electronic Cigarettes

Inclusion Criteria: 1. Aged 21-60 2. Smoke filtered cigarettes/machine-rolled cigarettes (≥5 cigarettes per day) or daily e-cigarette use for past year. 3. No serious quit attempt in prior month. This includes use of any FDA approved smoking cessation medication (varenicline, bupropion \[used specifically as a quitting aid\], patch, gum, lozenge, inhaler, and nasal spray) in the past 1 month as an indication of treatment seeking. 4. Willing to supplement cigarette smoking with ECIG use for 4 weeks or replace e-cigarette with study product for 4 weeks 5. Willing to attend regular visits over a 4-week period (not planning to move, not planning extended vacation, no planned surgeries) 6. Willing to undergo two fMRI scans 7. Able to read and write in English 8. Able to understand and consent to study procedures 9. Access to computer with internet service that allows for use of Zoom Exclusion Criteria: 1. Impaired smell function as measured via a standardized screening assessment 2. Unstable or significant medical condition in the past 12 months (recent heart attack or some other heart conditions, stroke, severe angina including high blood pressure) 3. Severe immune system disorders (uncontrolled Human Immunodeficiency virus infection; unstable multiple sclerosis symptoms), respiratory diseases (exacerbations of asthma or chronic obstructive pulmonary disorder, require oxygen, require oral prednisone), kidney (dialysis) or liver diseases (cirrhosis), or any medical disorder/medication that may affect participant safety or biomarker data 4. Women who are pregnant (verified by urine pregnancy test at any visit), trying to become pregnant, or nursing 5. Medical conditions associated with cognitive impairment or neurological dysfunction 6. Severe claustrophobia 7. Current depressive or anxiety disorder 8. Uncontrolled mental illness or substance abuse or inpatient treatment for these conditions in the past 6 months 9. Use of illicit drugs or prescription drugs for non-medical use daily/almost daily or weekly in the past 3 months per National Institute on Drug Abuse (NIDA) Quick Screen, not including use of marijuana 10. Any known risk from exposure to high-field strength magnetic fields (e.g., cardiac pacemakers), any irremovable metallic foreign objects in their body (e.g., braces), or a questionable history of metallic fragments which are likely to create artifact on the MRI scans 11. Known allergy to propylene glycol or vegetable glycerin 12. Other member of household currently participating in the study 13. History of a seizure disorder or had a seizure in the past 12 months 14. Currently taking medications prescribed to prevent seizures (such as Carbamazepine or Phenobarbital). Using seizure medications for off-label use (indications other than treatment for seizures) will not be included as an exclusion, these will be assessed on a case-by-case basis