Table 1 Inclusion and exclusion criteria for study participation

Inclusion criteria

• Adults 18–50 years old

• Daily smokers for ≥ 12 months who smoke ≥ 10 cigarettes/day

• Fagerström test for nicotine dependence ≥ 3

• CO levels ≥ 11

• Not currently seeking treatment for nicotine dependence

• Clear urine drug screen (marijuana permissible)

• Not currently pregnant (females only)

• Regular menstrual cycle (females only)

Exclusion criteria

• Current major medical illness

• Lifetime history of psychotic disorder (DSM-IV)

• Other Axis 1 psychiatric disorder within past year (DSM-IV)

• Lifetime history of substance dependence disorder other than nicotine (DSM-IV)

• History of substance use disorder other than nicotine within past 2 years (DSM-IV)

• Heavy alcohol use within past year (> 7 drinks/week or > 3 drinks/occasion for females; > 14 drinks/week or > 4 drinks/occasion for males)

• Current regular use of any tobacco products other than cigarettes

• Current regular use of psychotropic medication

• Contraindications to progesterone use (e.g., thrombophlebitis, stroke)

• Known progesterone or peanut allergy (Prometrium^® contains peanut oil)

• Left-handed (for consistency in neuroimaging)

Weighs ≥ 300 lbs. (contraindication for fMRI)

• Metallic implants (contraindication for fMRI)

• Claustrophobic (contraindication for fMRI)