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What Is It?

The birth control shot is a long-acting form of progesterone, a hormone that is naturally manufactured in a girl's ovaries. The shot is given as an injection in the upper arm or in the buttocks once every 3 months to protect a girl from becoming pregnant.

How Does It Work?

The hormone progesterone in the birth control shot primarily works by preventing ovulation (the release of an egg during the monthly cycle). If a girl doesn't ovulate, she cannot get pregnant because there is no egg to be fertilized.

How Well Does It Work?

The birth control shot is a very effective method of birth control. Over the course of 1 year, fewer than 3 out of 100 typical couples who use the birth control shot every 3 months will have an accidental pregnancy. The chance of getting pregnant increases if you wait longer than 3 months to receive your next shot.

In general, how well each type of birth control method works depends on a lot of things. These include whether a person has any health conditions or is taking any medications that might interfere with its use. It also depends on whether the method chosen is convenient — and whether the person remembers to use it correctly all of the time.

Protection Against STDs

The birth control shot does not protect against sexually transmitted diseases (STDs). In fact there are studies that show that the birth control shot may possibly increase the risk of getting certain STDs. Scientists do not understand why, however.

Couples having sex must always use condoms along with the birth control shot to protect against STDs.

Abstinence (not having sex) is the only method that always prevents pregnancy and STDs.

Possible Side Effects

Many young women who receive the birth control shot will notice a change in their periods. Other possible side effects include:

  • irregular or no menstrual periods
  • weight gain, headaches, and breast tenderness
  • depression

The U.S. Food and Drug Administration (FDA) has issued a safety warning with regard to the use of the long-acting progesterone shot. Studies link this shot to a loss of bone density in women, although bone density may recover when a woman is no longer getting the shot.

Doctors are not sure how this type of shot may affect the bone density of adolescent girls in the future, though. So girls who are considering the shot as a method of birth control should talk to their doctors about it. Girls who are receiving the shot should make sure that they are getting enough calcium each day, either through their diet or by taking calcium supplements.

Girls who smoke should be sure to let their doctors know because smoking may be connected to this bone density loss. Smoking also increases a girl's chances of the other side effects of the shot.

Women may notice a decrease in fertility for up to a year after they stop getting the birth control shot. However, the shot does not cause permanent loss of fertility and most women can get pregnant once they stop getting the shot.

Who Uses It?

Every method of birth control should be considered in light of what works for the individual. Young women who have a hard time remembering to take birth control pills and who want extremely good protection against pregnancy use the birth control shot. Also, nursing mothers can use the birth control shot.

Not all women can — or should — use the birth control shot. In some cases, medical or other conditions make the use of the shot less effective or more risky. For example, it is not recommended for women who have had blood clots, certain types of cancers, or certain types of migraine headaches. Girls who have had unexplained vaginal bleeding (bleeding that is not during their periods) or who suspect they may be pregnant should talk to their doctors.

A girl who is interested in learning more about different types of birth control, including the shot, should talk to her doctor or other health professional.

How Do You Get It?

The shot must be prescribed and is given every 3 months in a doctor's office.

How Much Does It Cost?

Each injection (3 months' worth of birth control) costs about $60. Many health insurance plans cover the cost of birth control shots, as well as the cost of the doctor's visit. Family planning clinics (such as Planned Parenthood) may charge less.

Reviewed by: Mary L. Gavin, MD
Date reviewed: July 2013

Other Related KidsHealth Articles:
About Birth Control
Before you consider having sex, you need to know how to protect yourself. Read this article to get the basics on birth control.
About Sexually Transmitted Diseases (STDs)
You've probably heard lots of discouraging news about sexually transmitted diseases. The good news is that STDs can be prevented. Find out how to protect yourself.
Abstinence is the only form of birth control that is 100% effective in preventing pregnancy. Abstinence also protects people against STDs.
Birth Control Methods: How Well Do They Work?
Some birth control methods work better than others. This chart compares how well different birth control methods work.
Female Reproductive System
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Gyn Checkups
Girls should get their first gynecological checkup between ages 13 and 15. Find out what happens during a yearly gyn visit -- and why most girls don't get internal exams.
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Related Resources:
American College of Obstetricians and Gynecologists (ACOG)
This site offers information on numerous health issues. The women's health section includes readings on pregnancy, labor, delivery, postpartum care, breast health, menopause, contraception, and more.
GYT - Get Yourself Talking and Get Yourself Tested
This media campaign designed to get young people to talk with their health care providers and partners about the importance of getting tested for sexually transmitted diseases.
National Campaign to Prevent Teen and Unplanned Pregnancy
This site provides teen pregnancy facts, resources, and prevention tips.
Planned Parenthood Federation of America
Planned Parenthood offers information on sexually transmitted diseases, birth control methods, and other issues of sexual health.
Planned Parenthood Info for Teens
This site from the Planned Parenthood Federation of America has information on relationships and sexual health for teens.
U.S. Food and Drug Administration (FDA)
The FDA is responsible for protecting the public health by ensuring the safety, efficacy, and security of human and veterinary drugs, biological products, medical devices, our nation's food supply, cosmetics, and products that emit radiation.