Progesterone occurs naturally in the human body and is produced by the adrenal glands in both sexes, the ovaries in women, the placenta during pregnancy, and the testes in men. Progesterone has several important roles in women. It maintains a normal menstrual cycle and plays an important role during pregnancy by preparing the tissues lining the uterus for implantation by the fertilized egg. It also helps prepare the breasts for milk production. The growing fetus also uses Progesterone to produce steroid hormones that are essential for normal fetal development. Progesterone plays a protective role in preventing some breast and uterine cancers. It also stimulates normal bone growth and thyroid function.

When given as a supplement, Progesterone can help initiate and maintain a pregnancy. Short-term Progesterone and estrogen replacement therapy can help minimize some of the distressing symptoms of menopause, such as hot flashes. Progesterone may also help control dysfunctional uterine bleeding, painful periods, and overgrowth of the endometrial lining in postmenopausal women. As a birth spacing option, Progesterone prevents ovulation and prevents sperm from reaching the fallopian tube. Other uses of Progesterone are in the suppression of milk secretion following delivery, and in the treatment of certain endometrial cancers.

Progesterone is also an intermediate compound in the biochemical pathways that lead to the production of other important hormones such as testosterone, estrogen and cortisol. Testosterone plays a role in maintaining both the male and female sex drive, and also helps maintain strong bones and energy levels. Estrogen plays a key role in the development of female sexual characteristics and in the menstrual cycle. In post-menopausal women, estrogen decreases bone reabsorption, reverses atrophy of the vulva and vagina, and exerts a protective effect against cardiovascular disease. Cortisol plays a role in glucose metabolism, provides increased energy during periods of stress, and has an anti-inflammatory action.