Depo-Provera is a medication that should be injected every three months as a form of birth control. It can also treat endometriosis. Depo-Provera is an injection of progestin, a hormone that acts to prevent ovulation. Depo-Provera should be administered intramuscularly into the upper arm or buttocks by a qualified healthcare professional. This injection is usually given within five days after the onset of a normal menstrual period.