This within-subjects study aims to evaluate the effects of IQOS use on combustible cigarette smoking behaviors among 100 cigarette smokers who completed the study. After measuring baseline cigarette smoking rate, participants will receive an IQOS device and be instructed to use it (versus cigarettes) over a 14-day period. The investigators will also examine which objective and subjective effects of IQOS use predict a complete and incomplete switch from cigarettes to IQOS.

Inclusion Criteria:

1. Able to communicate fluently in English (i.e. speaking, writing, and reading).
2. Male and female smokers who are between 18 and 65 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. Not currently undergoing smoking cessation treatment or planning to quit smoking within the next 30 days.
4. Report an interest in quitting smoking within the next 6 months.
5. Plan to live in the area for the duration of the study
6. Willing to use study provided IQOS devices and HeatSticks during 2 laboratory visits and throughout study participation.
7. 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

1. Regular use of nicotine containing products other than cigarettes (e.g. chewing tobacco, snuff, snus, cigars, e-cigs, etc.). Participants agreeing to abstain from using nicotine containing products other than cigarettes for the duration of study will be considered eligible.
2. Current enrollment or plans to enroll in a smoking cessation program over the duration of the study (i.e. 21 days/3 weeks).
3. 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 and/or currently receiving medical treatment for substance abuse. Counseling and support groups (e.g. Alcoholics Anonymous and Narcotics Anonymous) will not be considered medical treatment for the purposes of this protocol.
2. Current alcohol consumption that exceeds 20 standard drinks/week.
3. Breath alcohol reading (BrAC) greater than .000 at Intake.

Medical

1. Women, including all individuals assigned as "female" at birth, who are pregnant, breast feeding, 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.

Psychiatric

1. Lifetime history of schizophrenia or psychosis.
2. Lifetime history or current diagnosis of active major depression. Participants who maintain a diagnosis of major depression who have not experienced any major depressive episodes in the past 6 months and are stable on antidepressant medication(s) are eligible to participate.
3. Lifetime history of a suicide attempt.

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.

1 month

Adverse Events were defined as any unexpected event related to IQOS use.

Serious Adverse Events were defined as any severe or serious event related to IQOS use.