Injection (Depo-Provera)

Depo-Provera is the only injectable contraceptive available in the United States. Each injection contains high doses of the hormone progestin, which prevents pregnancy for up to three months.

Effectiveness rate. Depo-Provera is highly effective in preventing pregnancy, even if a woman is a few days late in receiving a scheduled dose. It's also ideal for women who aren't likely to, or don't want to, take a pill every day. The typical effectiveness rate among users is 97 percent, meaning that three out of 100 women using the injection for one year will get pregnant.

Side effects and health risks. You'll experience changes in your menstrual periods while using Depo-Provera. Periods may become irregular or unpredictable, or you may not bleed at all. The absence of periods isn't harmful, and periods typically return to normal after you stop using Depo-Provera. Other side effects may include weight gain, breast tenderness and depression. However, women who take Depo-Provera don't experience the side effects of estrogen exposure, such as an increased risk of blood clots and cardiovascular disease. The injection doesn't protect against STDs.

Prolonged use of Depo-Provera may result in bone loss, during use, but bone density returns to normal when you stop using Depo-Provera.

The return of normal menstrual periods after Depo-Provera can be delayed, sometimes for months. As a result, you may not experience a prompt return to fertility after stopping the injections.

How to use Depo-Provera. If you decide on Depo-Provera, you receive an injection in your upper arm or buttocks every three months. You should get the first injection within the first five days of your menstrual period for immediate effectiveness. If you get the first injection later than that, use a backup method of birth control for two weeks.

Cost and availability. Depo-Provera costs between $30 and $75 per injection, which lasts three months. The initial examination costs $35 to $125. Further office visits cost $20 to $40.