The Role of Flavor in the Substitutability of E-cigarettes for Combustible Cigarettes Among Persistent Smokers

Inclusion Criteria: 1. Able to communicate fluently in English (i.e. speaking, writing, and reading) 2. Male and female smokers who are \> 21 years of age and self-report smoking at least 5 cigarettes (menthol and/or non-menthol) per day for at least the last 12 months 3. 5 or more failed quit attempts and the use of smoking cessation medication on at least one prior attempt. 4. Ever use of an e-cigarette 5. Have a carbon monoxide (CO) greater than 10 ppm 6. Not using any forms of nicotine regularly other than cigarettes 7. Be willing to switch to e-cigarettes for 6 weeks and use the assigned flavors 8. Plan to live in the area for the duration of the study 9. Capable of giving written informed consent, which includes compliance with the requirements and restrictions listed in the combined consent and HIPAA form. Exclusion Criteria: Smoking Behavior Regular use of nicotine-containing products other than cigarettes (e.g., chewing tobacco, snuff, snus, cigars, e-cigs, etc.). Regular e-cigarette use is defined as greater than 5 days/past 30 days 1. Participants agreeing to abstain from using nicotine-containing products other than cigarettes for the duration of the study will be considered eligible. 2. Current enrollment or plans to enroll in a smoking cessation program over the duration of the study. 3. Current use of smoking cessation medication 4. Provide a CO breath test reading less than 10 ppm at Intake. Alcohol and Drug 1. History of substance abuse (other than nicotine dependence) in the past 12 months. 2. Current alcohol consumption that exceeds 20 standard drinks/week. 3. Current use of recreational drugs (other than nicotine and cannabis) 4. Breath alcohol reading (BrAC) greater than .000 at Intake. Medical 1. Women, including all individuals assigned as "female" at birth, who are pregnant, breastfeeding, or planning a pregnancy over the duration of the study period. 2. Serious or unstable disease within the past year (e.g. cancer, heart disease). Applicable conditions will be evaluated on a case-by-case basis by the Principal Investigator. 3. Allergies to either propylene glycol or flavor additives Psychiatric 1\. Lifetime history of schizophrenia or psychosis. General Exclusion 1. Past, current, anticipated, or pending enrollment in another research program over the study period that could potentially impact subject safety, study data, and/or the study design as determined by the Principal Investigator. 2. Any medical condition, illness, disorder, adverse event (AE), or concomitant medication that could compromise participant safety or significantly impact study performance as determined by the Principal Investigator. Subjects may be deemed ineligible for any of the aforementioned reasons at any point throughout the study, as well as during the initial telephone screen. 3. Significant non-compliance with protocol and/or study design as determined by the Principal Investigator and/o. Subjects may be deemed ineligible at any point throughout the study.