Emergency contraception (EC) is used to prevent pregnancy in the case of birth control failure (for example, a broken condom) or unprotected intercourse (for example, because of rape or carelessness/wishful thinking)1.
There are two kinds of EC: a post-coital intrauterine device (IUD) that is inserted by a physician up to seven days after the "emergency"; and a hormone pill (emergency contraceptive pill or ECP), also called a morning after pill.
ECP may be progestin only, or a combined estrogen/progestin type which is basically a regular birth control pill given at higher dose over a brief period. Both methods work best if they are used within 72 hours of unprotected intercourse, and the sooner they are taken, the more effective they are; they are thought to be between 75-89% effective in preventing unwanted pregnancy. Side effects include nausea and vomiting, which are more common with combined pills than progestin only forms. Though these side effects are unpleasant, ECP is considered to be very safe, only contraindicated for women who are pregnant. Depending on the jurisdiction, ECP may require a physician’s prescription or may be dispensed over the counter by a pharmacist. If you normally take birth control pills and simply forgot, you can use your regular pills as ECP.
ECP is often confused with RU-486 (mifepristone), a drug which induces abortion in an already established pregnancy; thus RU-486 is said to result in medical (as opposed to surgical) abortion. By contrast, ECP is not an abortifacient and does not disrupt an established pregnancy. Instead, it prevents conception from taking place. This may make ECP more palatable for those who oppose abortion on moral and ethical grounds.
IUD EC is thought to be 99% effective in preventing pregnancy; side effects include heavier-than-normal cramping and bleeding during regular menstruation; and, for women with multiple sexual partners, increased risk of potentially dangerous pelvic infection. On the plus side, IUDs can be left in place to function as longer-term birth control.
EC should not be used as a primary form of birth control because it is not as effective as other methods. It should only be used, as the name suggests, in emergencies. Nevertheless, many physicians and birth control activists have come to believe that EC is underused, and that if it were more accessible it would help to prevent many unwanted pregnancies, particularly among teenage women, thus improving the health of women and children.
Planned Parenthood has a chart which explains how to use various brands of regular birth control pills as ECP at www.plannedparenthood.org/library/BIRTHCONTROL/EmergContra.htm.
1Actually, pregnancy will result from unprotected intercourse only 8-9% of the time. If women know how to recognize their fertility cycles, they stand a much better chance of knowing whether the broken condom/contraception-less act will actually result in conception, or whether the time is just not right for that.