The first drug, mifepristone, blocks the reproductive hormone progesterone, and the second, misoprostol, taken one or two days later, prompts contractions and helps the uterus expel its contents.
More than five million women have used mifepristone to terminate their pregnancies in the United States, and dozens of other countries have approved the drug for use.
The case reached the justices after a swift-moving and tangled fight over the pill’s legal status.
In November, the plaintiffs filed a lawsuit in the Amarillo division of the federal court system in Texas, guaranteeing that the case would come before a single judge: Matthew J. Kacsmaryk of the U.S. District Court for the Northern District of Texas.
Judge Kacsmaryk, an appointee of Mr. Trump, is a longtime opponent of abortion and joined the bench after working at First Liberty Institute, a conservative legal group that focuses on issues of religious liberty.
The coalition that brought the suit, the Alliance for Hippocratic Medicine, argued that the F.D.A. had improperly approved the pill in 2000 and that mifepristone is unsafe. The agency has strongly disputed those claims, pointing to studies that show that serious complications are rare and that less than 1 percent of patients need hospitalization.
This month, Judge Kacsmaryk, in a temporary ruling, declared invalid the F.D.A.’s approval of the drug and gave both parties a week to seek emergency relief before the decision took effect.
Less than an hour later, a federal judge in Washington State, Thomas O. Rice, an appointee of President Barack Obama, issued a contradictory ruling in a separate lawsuit over mifepristone. Judge Rice blocked the F.D.A. from limiting the availability of the pill in 17 states and the District of Columbia, which were parties in that suit.
