Facebook Tweet Share

Main Content

Sexual and Reproductive Health

Birth Control Injection


What is the birth control injection?


The birth control injection is given to help prevent pregnancy. It contains one hormone (progestin). It doesn’t contain estrogen.

The birth control injection prevents pregnancy by:

  • stopping your body from releasing an egg. If you don’t release an egg, you can’t get pregnant
  • decreasing the amount of cervical mucous and making it thicker. This slows the movement of sperm, making it harder for them to get to the uterus
  • making the lining of the uterus thin

How well does the injection work?

  • There’s about an 85% chance of getting pregnant after 1 year of having unprotected sex.
  • With typical use (this means not following the exact directions) the injection is 94% effective.
  • With perfect use (this means you follow the exact directions all the time) the injection is 99.8% effective.
  • The injection doesn’t protect you from sexually transmitted infections (STIs) and HIV.
  • Use a condom every time you have sex (vaginal, oral, or anal) to lower your risk of STIs and HIV.

How do I use the injection?

The birth control injection is given by a health care provider. You need a prescription for the injection. It needs to be given every 12 to 13 weeks in the arm or buttocks.

There are different ways to start the injection. If you get your first injection:

  • during the first 5 days of your period, it takes 24 hours to become effective. Consider using an extra form of birth control (e.g., condoms, abstinence) during this time
  • at any other time, you need to use an extra form of birth control (e.g., condoms, abstinence) for 7 days

How will the injection affect my period?

You can have spotting or bleeding between periods. If the bleeding is heavy or doesn’t stop, talk to your health care provider.

Your period might stop. After one year, 46% of people stop having a period. After 2 years, up to 68% of people stop having a period. This is not harmful.

What are the benefits of the injection?

  • It can be used by people who can’t take estrogen because of health problems.
  • One injection lasts 12 weeks.
  • It may lower your risk of endometrial and ovarian cancer.
  • It might decrease period cramps.
  • It might decrease symptoms of endometriosis, premenstrual syndrome (PMS), and chronic pelvic pain.

What are the side effects of the injection?

The injection can cause:

  • mild headaches
  • acne
  • depression
  • tender breasts
  • less interest in sex
  • upset stomach (nausea)
  • weight gain

If you are concerned about the side effects, talk to your health care provider.

What are the risks of the injection?

When you stop getting the injection, it can take several months for your body to start to release eggs. After people stop using the injection, about 50% will be pregnant at 1 year and about 90% will be pregnant by 2 years if not using any other birth control method.

The injection can increase your risk of thinning bones (bone mineral loss or osteoporosis). Bone mineral loss is usually temporary and goes away when you stop. The risk may increase if you are on the injection for a long time. If you’ve used the injection for 2 years, talk to your health care provider about bone mineral loss.

Is there anything that increases my risk of bone mineral loss?

The risk of thinning bones is higher if you:

  • have weak or brittle bones
  • have a family history of osteoporosis
  • have a small body frame
  • have an eating disorder
  • smoke
  • exercise very little or not at all
  • eat or drink lots of caffeine or alcohol
  • take steroids (e.g., prednisone)

You can help keep your bones healthy if you:

  • eat foods high in calcium and vitamin D (e.g., milk, yogurt)
  • take calcium and vitamin D supplements (talk to your pharmacist)
  • don’t smoke
  • limit alcohol and caffeine
  • do weightbearing exercises (e.g., walk, run, or dance) every day

What if I miss or I’m late for my injection?

If your last injection was 13 to 14 weeks ago, you should still be protected from pregnancy. You need to have your injection right away and before 14 weeks have passed.

If your last injection was over 14 weeks ago:

  • use a backup form of birth control
  • see your health care provider right away for your next injection
  • if you’ve had unprotected sex, get emergency contraception (Levonorgestrel or copper IUD)

Did You Know

  • You have the right to make the decision to have sex or not.
  • Plan ahead and talk to your partner about how to protect yourself and lower your risk of pregnancy, STIs, and HIV. Use a condom every time you have sex.
  • Many sexual health clinics offer some types of birth control for no cost for those who qualify.
  • You can get pregnant as soon as you stop using the injection, even if your periods are not regular.
  • The injection is not affected by most medicines.
  • Don’t use the injection if you’re pregnant or think you might be.

For More Information

  • Health Link – Health Advice 24/7: 811

Go to Top