Progesterone and Brain Imaging Study

The purpose of this study is to learn whether a sex hormone called progesterone is helpful in reducing cigarette smoking and craving for cigarettes. This study also includes brain imaging to measure possible effects of progesterone on certain neurochemicals. These neurochemicals are called gamma-aminobutyric acid (or GABA for short) and glutamate. Both nicotine and progesterone affect these brain chemicals. Individuals wishing to participate in this study must be medically healthy men or women who smoke at least 10 cigarettes per day or greater. Participants must not suffer from a mental illness or use drugs other than nicotine and marijuana. Participants cannot have any implanted metallic devices such as pacemakers, orthodontic braces, or shrapnel. Participants must not have peanut allergies and must never have had a reaction to progesterone. Finally, participants cannot be taking any medications for anxiety, depression or insomnia.