Morning after pill

Originally Published: December 21, 1995 - Last Updated / Reviewed On: March 20, 2014
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Dear Alice,

How long after having had sex is the taking of the morning after pill useful?

—Intrigued

Dear Intrigued,

Also known as emergency contraception, the "morning after pill" contains a high dose of hormones (found in daily birth control pills) to prevent pregnancy after sex that has occured when a birth control method failed or was not used. Research suggests that though it is recommended that you take it within 72 hours after sex, it is moderately effective up to 120 hours (or five days) after sex. However, even though it's referred to as the "morning after pill," you don't have to wait for the sun to come up. The sooner it is taken, the more effective it is. Emergency contraception (EC) is not to be confused with RU-486 (mifepristone), a pill that causes medical abortion in pregnant women within 49 days from the first day of their last menstrual period.

There are two forms of hormonal EC, and they may work in several ways: by delaying or inhibiting release of an egg (ovulation), preventing the egg and the sperm from meeting (fertilization), or keeping a fertilized egg from attaching to the uterine wall (implantation). If started within 72 hours of unprotected intercourse, progestin-only EC is more effective (89% efficacy) than combined hormonal pills that contain estrogen and progestin (75% efficacy). Users are also less likely to have nausea and vomiting from taking progestin-only EC than from the combined regimen. The most common form of EC is called Plan B, and it contains progestin as its only hormonal ingredient.

It's normal for some women to have irregular periods or unexpected bleeding after using EC. Women who don't get their periods within three weeks should visit a health care provider. Temporary side effects of using EC may include:

  • headache
  • dizziness
  • cramping and abdominal pain
  • breast tenderness

Plan B One-Step and its generic versions are now being made available on-the-shelf at many pharmacies and drugstores and you don't need a prescription or proof-of-age in order to purchase them. Because it's important to take EC as soon as possible after sex, this is a critical advance. You might consider having some EC on-hand, so that if you need it, you can take it as soon as possible. It's good to note, however, that hormonal EC is not intended to be used as a regular form of birth control.

Knowing that you have options can provide a tremendous sense of security. If you missed the 120-hour window, you can take a pregnancy test. If you're pregnant, talking about your options with a health care provider may help you decide what to do next.

Alice