Several options are available to women who want long-term, but not permanent, protection against pregnancy. These options rely on estrogen-progestin or progestin alone to prevent ovulation. They include:

Shot/Injection

With this method you get injections, or shots, of the hormone progestin (Depo-Provera (DMPA), or the low-dose form, Depo-Subq-Provera) in the buttocks or arm every three months. A new type is injected under the skin. The birth control shot stops the ovaries from releasing an egg in most women. It also causes changes in the cervix that keep the sperm from joining with the egg.

Depo-Provera should not be used more than 2 years in a row because it can cause a temporary loss of bone density. The loss increases the longer this method is used. The bone does start to grow after this method is stopped. But it may increase the risk of fracture and osteoporosis if used for a long time. 

You may experience some changes in menstrual bleeding. Early on, you may have spotting. Later, you may stop having your period altogether.

Benefits
Progestin shots have been shown to reduce the risk of uterine (endometrial) cancer and prevent anemia, ectopic pregnancy and pelvic inflammatory disease.

Possible side effects
Bloating/weight gain, headaches, depression, loss of interest in sex and hair loss are the most common side effects, and it usually takes 12 weeks before the effects of the shot disappear. Recent studies show a link between Depo-Provera and a loss of bone density, which can lead to an increased risk of osteoporosis. The bone density loss may not return completely after discontinuing Depo-Provera.