How Does the Morning-after Pill Work?


Plan B One-Step Plan B One-Step
Morning-after pills like Plan B One-Step can reduce a woman's chance of getting pregnant by between 75 and 89 percent if she takes it within three days of unprotected sex. Getty Images/Stringer

For any woman concerned about unplanned pregnancy, one night of sex with a failed contraceptive can be terrifying. Why? Because that's all it takes to become pregnant. But things changed a little on Aug. 24, 2006, when the U.S. Food and Drug Administration approved the morning-after pill.

The morning-after pill is a form of emergency contraception you can be use to prevent pregnancy if you've had unprotected sex or your birth control method failed. The emergency contraception is designed specifically as backup contraception only, and not as a primary method of birth control. Most emergency contraceptive pills are sold over the counter to anyone.

Types of Emergency Contraception Pills

Unlike the birth control pill, which you take on a daily basis to prevent pregnancy, emergency contraceptive pills should only be taken when your regular contraception fails (i.e. your condom breaks), or you have sex without any kind of contraceptive. There are two types of morning-after pills: those that include levonorgestrel and those with ulipristal acetate. There are several brand-name versions of the morning-after pill that contain levonorgestrel, including Plan B One-Step, Take Action, My Way and AfterPill. These are available over the counter at your pharmacy; you can even order them online. Levonorgestrel morning-after pills can lower your chance of getting pregnant by between 75 and 89 percent when you take it within three days of unprotected sex.

Ella is the only morning-after pill with ulipristal acetate, and it requires a prescription from your doctor or nurse practitioner. Ella is more effective than levonorgestrel morning-after pills because you can take it up to 120 hours (five days) after unprotected sex. It reduces your chances of getting pregnant by 85 percent if you take it within five days of unprotected sex.

When to Take Emergency Contraception Pills

If you use emergency contraception correctly, you're much less likely to get pregnant. But exactly when should (and shouldn't?) you take a morning-after pill?

You should take a morning-after:

  • If you didn't use any birth control method when you had vaginal sex
  • If you botched your regular birth control (forgot to take your pill, change your patch, etc.) and had sex
  • If your partner's condom broke or slipped off after ejaculation
  • When your partner didn't pull out
  • If you were forced to have unprotected vaginal sex

There are times when you shouldn't use emergency contraception:

  • Don't use the morning-after pill as your regular form of birth control
  • Do not use Ella more than once during the same menstrual cycle
  • Don't use two different kinds of morning-after pills (like Plan B and Ella) at the same time

How Morning-after Pills Work

Morning-after pills like Plan B One-Step and Ella lower the risk of pregnancy by delaying or stopping the release of an egg from your ovary. Once an egg is released from your ovary, it usually lives in your reproductive system for about 12 to 24 hours. Sperm, though, can live inside the female reproductive system for as many as five days just waiting for an egg to show up. If you ovulate during that time, the sperm and egg can meet and cause pregnancy. If you take a morning-after pill, any swimmers left lingering around your uterus can't reach an egg to fertilize it, therefore a pregnancy is prevented from ever happening.

Morning-after pills won't work, however, if you've already started ovulating. And since most women don't know exactly when they ovulate, it's imperative to take the morning-after pill as soon as you have unprotected sex, no matter where you are in your menstrual cycle. In fact, Katherine Farris, M.D., a fellow with Physicians for Reproductive Health and affiliate medical director at Planned Parenthood South Atlantic, told Cosmopolitan she thinks women should always keep a few doses of the morning-after pill on-hand so they don't have to rush to the pharmacy in an emergency. (If you do stock up, store your pills where it's not super moist, so probably not the medicine cabinet in your bathroom!)

Are They Safe?

Emergency contraceptive pills are safe for most women, though some women may experience side effects like nausea or vomiting, dizziness, headache, breast tenderness, spotting between periods or heavier menstrual bleeding, and abdominal pain or cramps. These should last only a few days, if at all. Taking a morning-after pill could delay your period, so don't be alarmed. If you don't get your period within three to four weeks after taking an emergency contraceptive pill, take a pregnancy test.

You should contact your doctor if bleeding or spotting lasts for more than a week, or you have severe lower abdominal pain three to five weeks after taking a morning-after pill. You should also call your doctor or health care provider if you vomit within two hours after taking the pill to see if you need another dose.

Last editorial update on Jun 5, 2019 06:24:49 pm.

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