Medroxyprogesterone intramuscular (into a muscle) injection and medroxyprogesterone subcutaneous (under the skin) injection are used to prevent pregnancy. Medroxyprogesterone subcutaneous injection is also used to treat endometriosis (a condition in which the type of tissue that lines the uterus (womb) grows in other areas of the body and causes pain, heavy or irregular menstruation [periods], and other symptoms). Medroxyprogesterone is in a class of medications called progestins. It works to prevent pregnancy by preventing ovulation (the release of eggs from the ovaries). Medroxyprogesterone also thins the lining of the uterus. This helps to prevent pregnancy in all women and slows the spread of tissue from the uterus to other parts of the body in women who have endometriosis. Medroxyprogesterone injection is a very effective method of birth control but does not prevent the spread of human immunodeficiency virus (HIV, the virus that causes acquired immunodeficiency syndrome [AIDS]) or other sexually transmitted diseases.