Uses: This medication is used to increase your appetite and to prevent or reverse significant weight loss (e.g., muscle wasting in cancer or AIDS). By preventing weight loss from disease, you will feel better and may be able to be more active. This medication may also be used to treat cancer of the breast or uterus. It may be used alone or with other treatments, including surgery and radiation, to stop the growth of your tumor. Megestrol is similar to a natural substance made by the body called progesterone. It is not known how megestrol helps appetite or stops tumor growth.