Depo-Provera is a synthetic hormone which acts like the female hormone progesterone. It prevents pregnancy by stopping the egg from being released from a patient’s ovaries. It also causes cervical mucus to thicken making it difficult for sperm to enter the uterus. Depo-Provera is 99% effective in preventing pregnancy. Depo-Provera is administered every three months by injection into a patient’s arm or buttocks. A patient can stop receiving the injection at any time, with decreased fertility only in the first 12-18 months after stopping. Depo-Provera can be taken at any age. Patients taking Depo-Povera may experience changes in menstrual flow such as heavy, irregular, or no bleeding. Some patients may also experience side effects such as: Weight gain, headaches, cramping, breast tenderness, and depression. People who have had a history of liver disease or blood clots cannot take Depo-Provera, nor can a woman with breast cancer.