Progesterone is a female hormone important for the regulation of ovulation and menstruation. Progesterone is also important for the proper implantation of an embryo in the endometrium and for maintenance of the pregnancy. In women who are not pregnant and have not gone through menopause, this medication is used to: * restore normal menstrual periods that have stopped for several months (amenorrhea) * treat abnormal bleeding from the uterus that is due to low hormone levels * treat endometriosis