The morning-after pill contains a higher dose of the female progestin hormone than is in regular birth control pills. Taking it within 72 hours of rape, condom failure or just forgetting regular contraception can cut the chances of pregnancy by up to 89 percent.
It works best within the first 24 hours. If a woman already is pregnant, the pill has no effect.
Absent an appeal or a government request for more time to prepare one, the ruling will take effect in 30 days, meaning that over-the-counter sales could start then.
Associated Press writer Larry Neumeister in New York contributed to this report.