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Women's Health

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Emergency Contraception - Topic Overview


A doctor or other health professional has to insert an IUD.

How well does it work?

Emergency contraception works very well. The sooner you use it, the more likely it is to prevent pregnancy. Overall:

  • Emergency contraception, such as Plan B, can prevent an average of about 74% of pregnancies.1
  • If a woman takes emergency contraception on the fourth or fifth day after unprotected sex, ulipristal (such as Ella) may work better than levonorgestrel (such as Plan B).2
  • The copper IUD is more than 99% effective. Only about 2 women out of 1,000 who use it for emergency contraception will get pregnant.3

If you haven't started your period within 3 weeks after using emergency contraception, get a pregnancy test.

Does it cause side effects?

Emergency contraception may cause some side effects.

  • Emergency contraception may cause spotting or mild symptoms like those of birth control pills. It usually doesn't cause nausea.
  • Birth control pills can cause nausea or vomiting. In some women, they can also cause sore breasts, fatigue, headache, belly pain, or dizziness.
  • An IUD may cause cramping and bleeding during the first few days after insertion.

Call your doctor if you have a headache, dizziness, or belly pain that is severe or that lasts longer than 1 week.

If you are already pregnant, most pills won't harm the fetus. But some pills, such as ulipristal, may cause problems with the pregnancy. More research is needed to know for sure. An IUD could cause problems with the pregnancy.

What else should you think about?

  • Emergency contraception pills won't protect you for the rest of your cycle. Use your regular method of birth control, or use condoms.
  • If you are overweight or obese, emergency contraception pills may not work as well to prevent a pregnancy. Talk with your doctor about methods of emergency contraception that aren't affected by a woman's weight, such as the copper IUD.
  • Unless you get an IUD, emergency contraception does not take the place of regular birth control. Find a good method of birth control you can use every time you have sex.
  • Emergency contraception does not prevent sexually transmitted infections (STIs). If you are worried you might have been exposed to an STI, talk to your doctor.
  • Accidents can happen. It is a good idea to keep a set of the pills on hand in case you ever need it.

WebMD Medical Reference from Healthwise

Last Updated: July 18, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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