Depo-Provera, also known as “the shot,” is a hormonal method of birth control that only contains one hormone: progesterone. It stops a female from releasing eggs and also causes thickening of the cervical mucus.

Depo-Provera is ideal for girls who can’t take estrogen (the other hormone in birth control pills) or have trouble remembering to take the Pill every day on time. It’s also a good choice for girls who take medicines that interfere with the effectiveness of the Pill, like antibiotics that are long-term. Depo-Provera 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 the shot is administered 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; this is perfectly normal because the shot also thins the lining of the uterus so there’s nothing to shed each month. Some also report headaches, mood changes and weight gain. Depo-Provera offers NO protection against sexually transmitted diseases (STDs), so using a condom or other back up method is a good idea.

Like other hormonal methods, a prescription is needed to get the shot. The cost varies, depending on where she goes. Usually, you’ll pay less at a family planning clinic, like Planned Parenthood, than you will at a private doctor’s office. Some insurances also cover Depo-Provera, but if you use your parents’ insurance they will likely know you’ve been to the clinic. When you call to make the appointment, remember to ask.

For more information, go to “the shot,” or call 1-866-554-DEPO (3376) which offers a service that reminds you when you need to get your next shot.