WASHINGTON (AP) — The Biden administration is preparing for a worst-case scenario if a conservative federal judge rules in favor of a lawsuit seeking to restrict access to one of the two drugs typically used to induce a medicated abortion.

Two drugs, mifepristone and misoprostol, can be taken by women at home and are used for just over half of U.S. abortions. But that could be quickly changed by a lawsuit filed by an anti-abortion group in Texas that claims the Food and Drug Administration wrongly approved mifepristone for use more than 23 years ago.

The case is before a federal judge appointed by former President Donald Trump. A ruling in favor of the abortion opponents could immediately shut down the sale of the drug, but women would still have access to medicated abortions with a regimen of misoprostol.

Vice President Kamala Harris promised on Friday that the White House would push back on efforts to ban the drug, as she gathered a group of nearly a dozen doctors and abortion rights advocates to discuss a plan for responding to the looming threat to access to medical abortions.

"There are now partisan and political attacks attempting to question the legitimacy of a group of scientists and doctors who have studied the significance of this drug," Harris said. "There is now an attempt by politicians to remove it from the ability of doctors to prescribe and the ability of people to receive."

The lawsuit against mifepristone was filed by the Alliance for Defending Freedom, which was also involved in the Mississippi case that led to Roe v. Wade being overturned. It's the latest fallout in the struggle over reproductive care that the Democratic administration must grapple with since the Supreme Court overturned the constitutional right to an abortion last year.

Harris did not publicly lay out how the administration plans to respond if a ruling that halts the sale of the drug nationwide comes down on Friday.

Health and Human Services Secretary Xavier Becerra, meanwhile, was in California on Friday to meet leaders from Planned Parenthood to talk about access to the abortion drugs.

Dr. Kristyn Brandi said she told the vice president Friday that the ruling could trigger widespread confusion over the accessibility of medicated abortion in the U.S. Brandi, who is chair of the Physicians for Reproductive Health, said she already fields calls at her New Jersey clinic from women asking if medicated abortion is legal in the state.

"It's a really important thing to communicate with people: medication abortion is not going away," Brandi said.

She added that Harris expressed support for immediately challenging the ruling if it shuts down access to mifepristone.

Clinics and telehealth providers have been preparing for a ruling that shuts down access to mifepristone, ordering more doses of misoprostol so they can offer medication abortions with just that one drug. They will have to change the way they counsel patients, telling them that misoprostol-only abortions are slightly less effective and sometimes more painful than abortions done with both drugs.

Abortions using both drugs "can be as effective as 98% or more," while misoprostol-only abortions are up to about 95% effective, Melissa Grant, chief operating officer of the Carafem abortion clinic, told The Associated Press.

Mifepristone dilates the cervix and blocks the action of the hormone progesterone, which enables a pregnancy to continue. Misoprostol causes contractions that empty the uterus. Typically, mifepristone is taken by mouth first, followed by misoprostol a day or two later.

Studies show medication abortions are safe and effective, though with a slightly lower success rate than ones done by procedure in a clinic.

With the Texas decision pending, a dozen Democratic-controlled states filed their own lawsuit in federal court against the FDA on Thursday in Washington. The lawsuit seeks to make it easier for woman to access the drug and alleges that several FDA requirements for prescribing and dispensing it are "burdensome, harmful and unnecessary."

When the FDA approved mifepristone in 2000 it placed several safety restrictions on its use, including limiting dispensing to specialty clinics and requiring women to pick up the drug in person. The Biden administration had sought to expand access to medicated abortions in light of the Supreme Court's ruling, with an FDA announcement this year that broadened the pill's access through retail and mail-order pharmacies.

But several limitations remain, such as one that doctors must be specially certified to prescribe the drug.

Several medical groups have long opposed those requirements, pointing to the low rate of side effects seen with mifepristone compared with other medications that don't carry any certification requirements.

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Health writer Matthew Perrone in Washington and national medical writer Lindsey Tanner in Chicago contributed to this report.