This study investigates the use of progesterone, a hormone given by mouth, to see if it can reduce the response of the heart's electrical activity to a specific drug. The study focuses on preventing changes in the heart's rhythm that can be caused by some medications, specifically looking at the QTc interval, which is a measure of the heart's electrical cycle.

Participants in this study will take part in procedures that include receiving either the investigational medication or a placebo. A placebo is an inactive substance that looks like the investigational medication but does not contain any medicine. The study aims to compare the effects of progesterone with other therapeutic approaches to see which is more effective in reducing the risk of heart rhythm changes.

• Who can participate: The study is open to postmenopausal women aged 50 or older who have not had menstrual periods for at least 365 days, as well as premenopausal women aged 21-40. Participants should not have a history of certain cancers or heart conditions, and should not be taking hormone replacement therapy or medications that affect the heart's rhythm.
• Study details: Participants will receive either the investigational medication or a placebo. Participants will follow study procedures to evaluate the effects on heart rhythm changes.