Clinical Definition

The morning-after pill is a form of emergency contraception, or the use of drugs or a device to minimize the chances of pregnancy after unprotected intercourse or contraceptive failure. Emergency copper intrauterine contraception (IUD) has the lowest failure rate, followed by mifepristone or ulipristal acetate, and then levonorgestrel. Emergency contraception may prevent pregnancy by delaying eggs from being released temporarily, stopping fertilization or hindering implantation of fertilized eggs.

In Our Own Words

Emergency contraception, also called the morning-after pill or EPOC for emergency post-coital oral contraception, is designed to prevent pregnancy after unprotected sex or failure of a birth control method.

When used within 72 hours of sex, different options have different levels of efficacy. It’s been estimated the copper intrauterine device prevents about 95 percent of expected pregnancies while emergency oral contraceptives prevent between 50 to 66 percent. Some oral agents are available over the counter; others require a prescription. A doctor can insert the emergency copper IUD. Mechanisms of contraception are thought to involve delay of release of eggs and prevention of fertilization or implantation.