How Does Emergency Contraception Work?

When you think you need emergency contraception, you need answers fast. The good news is you have a lot of reliable options that can help if you act quickly. Learn more about your choices and how they work.

Emergency Contraception Explained

It can help if you just had sex and something went wrong -- you forgot to use protection, you used it incorrectly, or the condom broke, for instance. It's also an important option for women who were forced to have sex.

By using emergency contraception within 3 days of sex (the sooner, the better), you can dramatically lower your chance of getting pregnant. It may also work up to 5 days after sex, though it won't be as effective.

How It Works

Emergency contraception pills use hormones or medications that block pregnancy. Most use the same hormones that are in regular birth control pills.

The emergency-use pills work mainly by delaying  the release of an egg or ovulation. Once implantation has occurred, emergency contraception is no longer effective. If you're already pregnant, these pills will have no effect as a contraception method.

Emergency contraception works well. But you should take it quickly -- preferably within 24 hours of sex. Yes, it's often called the "morning after" pill. But really, the sooner you take it, the more effective it will be. Studies show that if you take emergency contraception within 72 hours of sex, you have only a 1% to 2% chance of getting pregnant.

Types of Emergency Contraception

There are several kinds of pills, or an IUD.

There are 3 types of emergency contraception in pill form that are sold both with and without a prescription. You need to be 17 to buy them if a prescription is needed. Depending on the brand and dose, you might get 1 pill or 2.

1.  Pills containing a hormone called levonorgestrel:

  • My Way (over-the-counter) 
  • Plan B One-Step (over-the-counter) 
  • Preventeza (over-the-counter)
  • Take Action (over-the-counter)

You should use these drugs within 72 hours of having sex. They may still work up to 5 days later, but they're less effective with time. There are some differences among them. Plan B One-Step, and My Way are one pill. Some other generics are two pills that you take at the same time.


Until recently, you had to be 17 or older to get Plan B One-Step without a prescription. But the FDA removed the age restriction, so now people of any age should be able to buy Plan B One-Step without a prescription.

If you're 17 or older, you can get generic levonorgestrel -- like My Way -- without a prescription. If you're under 17, you need a prescription.

Emergency contraception in pill form begins to lose its effectiveness for women who are overweight or obese. The copper-T IUD is a more effective option. 

2. Birth control pills that contain progesterone and estrogen can also be used as emergency contraception. If you take them at a higher dose within 3 to 5 days of sex, they act as emergency contraception. This approach works, but is less effective than other forms of emergency contraception. Side effects, such as nausea, may also be worse. Do not take regular birth control this way unless you talk to your doctor first. Birth control pills require a prescription. 

3. Ulipristal (ella, ellaOne) is a third type of emergency contraception pill. You need a prescription to get it. This form of emergency contraception doesn't use hormones. Instead, it's a drug called ulipristal acetate that blocks the effects of your own hormones. It's effective up to 5 days after sex. You need a prescription to get it. If you think you may already be pregnant, check with a doctor before using Ella. If you are, you should not take this drug.

Copper-T IUD. This is a different approach. A doctor or health care provider will place a small plastic and copper IUD -- intrauterine device -- into your uterus. The copper works to prevent the sperm from fertilizing the egg, preventing pregnancy. The copper IUD is the most effective form of emergency contraception.

The advantage of the IUD is women can use it as long-term birth control -- it works for up to 10 years -- and also as emergency contraception if it is placed in the uterus within 5 days of sex. It may work better than pills, but getting it in time can be tricky.

A doctor or health care provider needs to put in the IUD. She'll also have to remove it before you can have children. This approach may be best for women who were already looking for long-term birth control.

WebMD Medical Reference Reviewed by Traci C. Johnson, MD on June 14, 2020



Kelly Cleland, MPA, MPH, researcher, Office of Population Research, Princeton University.

Anne Elizabeth Burke, MD, associate professor of gynecology and obstetrics, director of family planning, Johns Hopkins School of Medicine.

Alexandra Gold, MD, fellow in family planning, Johns Hopkins School of Medicine.

FDA: "FDA approves Plan B One-Step emergency contraceptive for use without a prescription for all women of child-bearing potential."

Gold, A. Contemporary OB/GYN, March 22, 2013. "Emergency Contraception."

International Consortium for Emergency Contraception: "The Intrauterine Device (IUD) for Emergency Contraception."

Office of Population Research at Princeton University: The Emergency Contraception Web Site: "Combined Emergency Contraceptive Pills ('Morning After Pills')," "Copper-T IUD as Emergency Contraception."

UpToDate: "Emergency Contraception." "Intrauterine Contraception."

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