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WITH the confirmation last week of John G. Roberts Jr. as chief justice of the United States, eyes turned to President Bush's next judicial nominee, who, on a closely divided court, may determine the fate of Roe v. Wade, the 1973 decision that recognized a woman's right to an abortion. But such speculation overlooks a paradox in the abortion wars: while combatants focus on the law, technology is already changing the future of abortion, with or without the Supreme Court.

Even if the court restricts or eliminates the right to an abortion, the often-raised specter of a return to back-alley abortions is not likely to be realized, said Dr. Beverly Winikoff, president of Gynuity Health Services, a nonprofit group that supports access to abortion. "The conditions that existed before 1973 were much different than what they are in 2005," she said. "We have better antibiotics now and better surgical treatments."

But no change is bigger than the advent of an inexpensive drug called misoprostol, which the federal Food and Drug Administration approved for treatment of ulcers in 1988, but which has been used in millions of self-administered abortions worldwide. If the Supreme Court overturns Roe v. Wade, freeing states to ban abortion, this common prescription drug, often known by the brand name Cytotec, could emerge as a cheap, relatively safe alternative to the practices that proliferated before Roe.

"We won't go back to the days of coat hangers and knitting needles," said Dr. Jerry Edwards, an abortion provider in Little Rock, Ark. "Rich women will fly to California; poor women will use Cytotec."

Because it was never intended for use in abortions, it has not been widely tested for safety and effectiveness.

In 2000, researchers at three obstetrics and gynecology clinics in New York noted that low-income immigrant women were already using misoprostol as an alternative to going to an abortion clinic, because it was easier and less expensive. They got the pills from doctors, pharmacies, relatives and from contacts in other countries.

The drug causes the uterus to contract and, if the contractions are strong enough, to expel the embryo or fetus. In the United States, misoprostol is typically used off label with the abortion drug RU-486 in non-surgical abortions and in some surgical abortions. A spokeswoman for Pfizer, which sells misoprostol under the name Cytotec, said the company does not comment on off-label use. Last year, Americans filled 365,000 prescriptions of misoprostol for ulcers, according to IMS Health, a pharmaceutical consulting firm.

A dose sufficient to cause an abortion costs less than $2, said Dr. John K. Jain, an associate professor of obstetrics and gynecology at the University of Southern California, who has performed limited clinical trials of abortions using misoprostol alone. He said he found that it was effective 80 to 90 percent of the time, if administered by a doctor. This is slightly lower than its effectiveness in combination with RU-486.

Misoprostol is usually used in the first trimester, but under clinical conditions, Dr. Jain and other researchers say it has been used safely and effectively in the second trimester. Women taking it on their own risk greater rates of failure and higher side effects, including nausea, vomiting, diarrhea and fever and chills.

Carrie Gordon Earll, a senior analyst of bioethics at Focus on the Family, which supports a reversal of Roe v. Wade, said the existence of new technologies like misoprostol should have no bearing on the law.

"The law operates as a teacher in a moral sense," regardless of people's opportunity to break it, she said. "Even if you have some people who get a drug off the black market and sell it to women, that doesn't mean we don't have a policy to discourage abortion."

In Brazil, where abortion is banned except in rare circumstances, misoprostol is the method of choice for up to 90 percent of all abortions, said Alessandra Chacham, a professor of sociology at the University of the State of Minas Gerais, who studies reproductive health in Brazil. In the late 1980's and early 1990's, she said, pregnant women started to spread the word, because the drug's label warned that it could cause miscarriages. Compared with illegal abortions using other methods, the rate of infection with misoprostol was 12 times lower, researchers have found. But researchers at the University of Rio de Janeiro reported that they also found that among babies born with certain birth defects, a high percentage of the mothers used misoprostol. When the government in response restricted access to misoprostol, drug smugglers created an illegal black market, Ms. Chacham said.

But American women may not be as receptive, said Norma McCorvey, who in 1973 was known as Jane Roe, the woman who brought the case that legalized abortion, but who has since argued for the reversal of the court's decision.

"When women start using these self-induced drugs, and start seeing body parts in their potty, they're going to go bananas," Miss McCorvey said. "And it's going to be horrible."

Dr. Jain said researchers still need to learn more about what happens when the drug doesn't work. Currently, if women fail to terminate a pregnancy using RU-486 and misoprostol, they still have a surgical abortion. But if abortion were illegal, many of these women might carry to term. "Data suggest it causes birth defects, including facial paralysis and limb defects," Dr. Jain said. "It's hard to quantify, but yes, there probably is a risk."

And widespread use of misoprostol could have another unintended consequence, said Mitchell Creinin, director of family planning at the University of Pittsburgh, who has run clinical trials on the drug. In Brazil, if women have problems with the drug, they go to the hospital to be treated for miscarriage. If women in the United States start using misoprostol for abortions, Dr. Creinin said, "someone going through a miscarriage is going to be looked at suspiciously, like, 'Did you do something?' "

Dr. Creinin added that "compared to when abortion was illegal before Roe, misoprostol is still safer." But as with any illegal drug, there is a period of elevated risk before users discover the proper dosages and protocols. If abortion became illegal, he said, "If I were a woman, I'd rather go to Brazil than Mississippi, because at least there they've learned how to do it."