Inclusion Criteria:

Female subjects aged 21-45 years with a smoking history of at least 20 cigarettes daily for at least 1 year. In good health as verified by medical history, screening examination, and screening laboratory tests. Not pregnant as determined by pregnancy screening nor breast feeding, and using acceptable birth control methods other than hormonal contraceptives.

Exclusion Criteria:

History of heart disease, peripheral vascular disease, COPD, liver diseases, abnormal vaginal bleeding, suspected or known breast malignancy, or any other medical condition which physician investigator deems inappropriate for subject participation. Use of regular psychotropic medication (antidepressants, antipsychotics, or anxiolytics) and recent psychiatric history. Amenorrhea. Current use of oral or other types of hormonal contraceptives. Abuse of alcohol or any other recreational or prescription drug. Regular use of any other tobacco products, including smokeless tobacco and nicotine products. Known allergy to progesterone or peanuts.