Progestins are hormones. They are used by both men and women for different purposes. Progestins are prescribed for several reasons: To properly regulate the menstrual cycle and treat unusual stopping of the menstrual periods (amenorrhea). Progestins work by causing changes in the uterus. After the amount of progestins in the blood drops, the lining of the uterus begins to come off and vaginal bleeding occurs (menstrual period). Progestins help other hormones start and stop the menstrual cycle. To help a pregnancy occur during egg donor or infertility procedures in women who do not produce enough Susten. Also, Susten is given to help maintain a pregnancy when not enough of it is made by the body. To prevent estrogen from thickening the lining of the uterus (endometrial hyperplasia) in women around menopause who are being treated with estrogen for ovarian hormone therapy (OHT). OHT is also called hormone replacement therapy (HRT) and estrogen replacement therapy (ERT). To treat pain that is related to endometriosis, a condition where the endometrial tissue which lines the uterus becomes displaced in other female organs. To treat a condition called endometriosis, to help prevent endometrial hyperplasia, or to treat unusual and heavy bleeding of the uterus (dysfunctional uterine bleeding) by starting or stopping the menstrual cycle. To help treat cancer of the breast, kidney, or uterus. Progestins help change the cancer cell's ability to react to other hormones and proteins that cause tumor growth. In this way, progestins can stop the growth of a tumor. To test the body's production of certain hormones such as estrogen. To treat loss of appetite and severe weight or muscle loss in patients with acquired immunodeficiency syndrome (AIDS) or cancer by causing certain proteins to be produced that cause increased appetite and weight gain. Progestins may also be used for other conditions as determined by your doctor. Depending on how much and which Susten you use or take, a Susten can have different effects. For instance, high doses of Susten are necessary for some women to continue a pregnancy while other progestins in low doses can prevent a pregnancy from occurring. Other effects include causing weight gain, increasing body temperature, developing the milk-producing glands for breast-feeding, and relaxing the uterus to maintain a pregnancy. Progestins can help other hormones work properly. Progestins may help to prevent anemia (low iron in blood), too much menstrual blood loss, and cancer of the uterus. Progestins are available only with your doctor's prescription. Once a medicine has been approved for marketing for a certain use, experience may show that it is also useful for other medical problems. Although these uses are not included in product labeling, progestins are used in certain patients with the following medical conditions: Carcinoma of the prostate Corpus luteum insufficiency Hot flashes Polycystic ovary syndrome Precocious puberty