The morning after pill is a prescription drug used to reduce the risk of pregnancy after an act of unprotected sexual intercourse. Also known as emergency contraceptive pills, they offer no protection against sexually transmitted diseases, and cannot be used to end a pregnancy. These drugs are only used as a preventative measure against pregnancy.

A form of emergency contraception, the morning after pill may be used to prevent pregnancy after:

• Intercourse in which no contraception was used
  
• Intercourse in which contraception failed (e.g., the condom broke)
  
• Intercourse in which contraception was used incorrectly (e.g., birth control pills were not taken properly)

Although emergency contraceptive pills are referred to as “the morning after pill,” the drug is never taken as a single dose. Instead, the pills are taken in two doses. The first dose may be taken up to 72 hours (three days) after an act of unprotected intercourse, and the second dose should be taken 12 hours after the initial dose.

The pills contain high doses of estrogen and progestin (a synthetic form of progesterone), hormones that are also found in birth control pills. Some brands contain both hormones, others contain only progestin. The hormones work to lower the risk of pregnancy by preventing:

• Ovulation (the release of an egg by an ovary)
• Fertilization (the penetration of an egg by sperm)
• Implantation (the embedding of a fertilized egg into the lining of the uterus)

The hormones are usually successful in preventing pregnancy when taken after intercourse because conception rarely occurs immediately. Instead, it occurs after ovulation, which may take place several days after the act of sexual intercourse.

Morning after pills are not the same as the “abortion pill.” Morning after pills prevent pregnancy by interfering with the conception process. The abortion pill, or medical abortion, is taken after a woman is pregnant. It induces a miscarriage by preventing the placenta from developing and expelling the egg from the uterus.

The National Women’s Health Information Center (NWHIC) estimates that emergency contraceptive pills containing a combination of estrogen and progestin are approximately 75 percent effective in preventing pregnancy. Pills that only contain progestin are approximately 89 percent effective. As well as being more effective, progestin-only pills also cause fewer side effects. Common side effects of the morning after pill include nausea and vomiting.

Taking the morning after pill may be risky for women with certain medical conditions, including a history of breast cancer or blood clots. For women with these conditions, an intrauterine device (IUD) may be used as an alternative method of emergency contraception. The device, which is inserted into the uterus by a physician, is also a good alternative for women who have waited longer than 72 hours to seek emergency contraception. When inserted up to seven days after intercourse, the device decreases the possibility of successful fertilization. 

Emergency contraceptive pills are not intended to be used as a woman’s regular form of contraception. However, in emergency situations they can be effectively used to prevent pregnancy. The Food and Drug Administration approved the sale of levonorgestrel (Plan B) without prescription for women aged 18 and older in August 2006.