Progesterone is one of the hormones that affects the female reproductive system. Its levels vary during the menstrual cycle and it is an ingredient of most birth control pills. It has a number of physiological effects, usually to normalize or restore changes to the body caused by estrogen. These effects include normalizing blood clotting and vascular tone, zinc and copper levels, cell oxygen levels, and use of fat stores for energy. Progesterone also assists in thyroid function and osteoblast bone building, and appears to prevent endometrial (cancer involving the uterine lining) and breast cancer.
Note that progesterone is a steroid hormone, and consists of four interconnected cyclic hydrocarbons. It is a hormone involved in the pregnancy and embryo development of humans. The chemical itself contains the ketone and aldehyde functional groups, as well as two methyl branches. Like all steroid hormones, it is hydrophobic. This is mostly due to its lack of very polar functional groups.