Depo-Provera is a birth control shot injected into the arm or buttocks. It is given every 12 weeks and is about 94% effective at preventing pregnancy. After the first injection, a backup birth control method (such as condoms) should be used for 7 days. Long-term use may lead to a decrease in bone mineral density, increasing the risk of osteoporosis, especially if used for more than 2 years or with a family history of the condition. Side effects include changes in menstrual cycle, injection site reactions (such as redness, itchiness), etc. It may take several months to regain fertility after stopping the shots. If severe side effects occur, contact your doctor immediately.