In an unsigned order, the justices blocked rulings by a Texas judge and the 5th Circuit Court of Appeals that could have sharply restricted use of the pills or taken them off the market entirely.
The vote was 7-2, with Justices Clarence Thomas and Samuel A. Alito Jr. dissenting.
More than 5 million women in the U.S. have used mifepristone since the Food and Drug Administration declared in 2000 that it was safe and effective.
The decision sends the case back to lower courts with a signal that most of the justices believe this challenge to the abortion pill will fail in the end.
The case posed the most important abortion question to reach the high court since last year’s 5-4 decision that overturned Roe vs. Wade and the constitutional right to abortion.
Though the three justices appointed by President Trump — Neil M. Gorsuch, Brett M. Kavanaugh and Amy Coney Barrett — voted last year to overturn Roe, they joined the court’s liberals and Chief Justice John G. Roberts Jr. on Friday to stay the Texas court rulings.
Since the overturning of Roe, Texas and a dozen other Republican-led states have essentially made abortion illegal and prohibited doctors from performing surgery or prescribing abortion pills.
The ruling by a Texas-based judge had threatened access to mifepristone in the states where abortion remains legal.
The threat to the abortion pills arose in the fall in Amarillo, Texas. A group of antiabortion advocates that included doctors set up an office there and filed a lawsuit to challenge the safety of mifepristone.
The pill had been used widely in Europe before the FDA approved its use in 2000. When taken in combination with misoprostol, the drugs cause cramping and bleeding; serious complications are “exceedingly rare,” the agency said.
Based on the safety record, the FDA relaxed regulations on mifepristone in 2016. Since then, patients need only a single visit to a healthcare provider, and they may use the medication through 10 weeks of a pregnancy, compared with seven weeks under the earlier regulations. Soon after President Biden took office, the FDA approved sending the pills through the mail.
But as widely predicted, U.S. District Judge Matthew J. Kacsmaryk, a Trump appointee, ruled for the antiabortion activists and revoked the FDA’s approval of the drug.
The Justice Department immediately appealed to the 5th Circuit Court. While one appellate judge would have put Kacsmaryk’s entire decision on hold, two others agreed with part of his ruling and suspended the FDA’s regulations from 2016 and beyond.
Solicitor General Elizabeth Prelogar sent an emergency appeal to the high court and urged the justices to block the lower court rulings. She said the abortion pills have a safety record of more than 20 years, and no federal judge had overruled the FDA’s judgment about the safety of a drug.