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Health Matters Fact Sheets

Birth Control Shot

(Updated December 2009, also available in Spanish)

What is the shot?

The birth control shot is an injection of a hormone called progestin. Each shot prevents pregnancy for about three months.

How effective is the shot?

The birth control shot is very effective. If always used correctly, less than 1 out of 100 women will get pregnant each year using the shot. If not always used correctly, 3 out of 100 women will get pregnant each year using the shot.

When you first start on the shot, it takes several days to begin working. Use a backup form of birth control for 7 days after you get the first shot.

How does it work?

A health care provider will give you the shot in your arm every 12 weeks. The hormone in the shot keeps your ovaries from releasing eggs and thickens your cervical mucus to block sperm from getting into the uterus.

What are the benefits of using the shot?

  • The shot is safe, convenient, and very effective.
  • If you use the shot, you don’t have to think about birth control every day or each time you have sex.
  • The progestin in the shot offers several health benefits, including fewer menstrual cramps, lighter or no periods. It also reduces the risk of pelvic inflammatory disease and endometrial cancer.
  • The shot can be a good birth control method for women who cannot use estrogen.

What are the downsides of using the shot?

  • The shot does not protect against sexually transmitted infections (STIs).
  • You must visit your health care provider every 12 weeks.
  • Some women may have side effects while using the shot. Irregular bleeding is the most common side effect, especially in the first 6 to 12 months. Other, less common, side effects include changes in appetite or weight gain, breast tenderness, and nausea and vomiting.
  • Women who use the birth control shot may have temporary bone thinning. Bone growth begins again when you stop using the shot. You can help protect your bones by exercising regularly and getting extra calcium and vitamin D.
  • Women can get pregnant after they stop using the shot, but it may take about a year after the last shot.
  • Women with certain conditions (history of or current breast cancer, anorexia, and steroid use) should not use the shot.

Where can I get the shot?

A health care professional can give you the shot in a medical office or clinic.

Where can I get more information?

For more information on the birth control shot, talk to your health care provider.

Compare the shot to other birth control options using ARHP’s Method Match at