Mexico's decision will transform family planning and cut down on backroom abortions, advocates said. Poor women in the countryside may benefit most. About half the population is poor.
Mexico's powerful Roman Catholic Church expressed outrage at the decision, and bishops threatened to excommunicate any woman who knowingly takes what the church calls an "abortion pill." For the church, terminating a fertilized egg is abortion.
Abortion remains illegal in Mexico except in cases of rape and to protect the health of the mother.
Taken within 72 hours of sexual intercourse, the pills work by preventing ovulation or fertilization of an egg. If fertilization has occurred, they prevent the egg from implanting into the uterus — the medical definition of pregnancy.
The policy change was included in a 60-page document published last week in the government's official gazette. The document revised a series of family-planning measures.
Catholic clergy denounced the pill's approval.
"Although they are called contraceptives, when they produce an abortion that's called murder, and it is not permitted to murder an innocent," Cardinal Norberto Rivera of Mexico City said Sunday.
Church officials said abortion is a sin punishable by excommunication, which does not require a formal decree. Those who "assist" in abortion are also subject to excommunication, although the church did not make clear who would fall into that category.
Anti-abortion groups called on President Vicente Fox to overturn the pill's approval, and the president's conservative National Action Party said it might oppose the decision as well.
"This amounts to the legalization of abortion in our country," said Rocio Galvez, head of the private group Pro-Vida, which means "pro-life."
"If we don't defend life at all times, then we will become a genocidal nation like the United States and those in Europe," she said, referring to countries where abortion is legal.
The "emergency pill," as the Mexican media call it, is sold under several brand names.
The Health Ministry calls it a contraceptive, and its makers say it is 85 percent to 90 percent effective. All women of reproductive age, including adolescents, can receive a prescription, according to the new guidelines.
In general, there is nothing to prevent foreign visitors to Mexico from receiving a prescription for the drug.
The government's decision caught women's-rights advocates by surprise.
"Society is advancing much more rapidly than the power structure," said longtime activist Patricia Mercado, referring to both church and state in this mostly Catholic nation. "There's really no going back."
The debate in Mexico is similar to one in the United States, where the drug has been available by prescription for years.
In December, a panel of the Food and Drug Administration recommended that it be made available over the counter. The FDA is expected to make a decision soon.
Many nations already have made it an over-the-counter drug. A few U.S. states allow pharmacists to dispense it directly.
The morning-after pill is made from the same hormones used in regular birth-control pills, but in a much higher dosage.
It is vastly different from RU-486 — the so-called abortion pill. RU-486 is designed to end a pregnancy and can be taken up to 12 weeks after conception. The morning-after pill is designed to prevent pregnancy and has no effect once a woman is pregnant.