Depo-Provera aka "the shot" is a hormonal method of birth control that only contains one hormone: progesterone. It stops a female from releasing eggs (aka ovulating) and also causes thickening of the cervical mucus.

Depo-Provera is ideal for women who can't take estrogen (the other hormone in birth control pills) and have trouble remembering to take the Pill every day on time, or who take medicines that interfere with the effectiveness of the Pill.

Depo users get an injection (shot) once every three months in their upper arm or upper buttocks/lower back. It's more than 99 percent effective at preventing pregnancy, as long as you get the shot on time.

The most common side effects are spotting and irregular bleeding, especially during the first few months of using the shot. Many girls eventually stop having periods. Some also report headaches, mood changes and weight gain. Depo-Provera offers NO protection against sexually transmitted infections, so a condom must also be used during intercourse.

Like other hormonal methods, you need a prescription to get the shot. The cost varies, depending on where you go. Usually, you'll pay less if you go to a family planning clinic, like Planned Parenthood ($35 per shot), versus a private doctor's office. But it really depends on whether or not you have health insurance. When you call to make the appointment, remember to ask.

For more information, go to "the shot," or call 1-866-554-DEPO (3376).