Progesterone is used as a part of hormone replacement therapy in women who have passed menopause (the change of life) and have not had a hysterectomy (surgery to remove the uterus). Hormone replacement therapy usually includes estrogen, which is used to treat symptoms of menopause and reduce the risk of developing certain diseases. However, estrogen can also cause abnormal thickening of the lining of the uterus and increase the risk of developing uterine cancer. Progesterone helps to prevent this thickening and decreases the risk of developing uterine cancer. Progesterone is also used to bring on menstruation (period) in women of childbearing age who have had normal periods and then stopped menstruating. Progesterone is in a class of medications called progestins (female hormones).