The lead plaintiff, the Alliance for Hippocratic Medicine, had initially challenged the FDA’s approval of mifepristone.

But the matter before the high court now is more narrow -- whether the FDA's subsequent regulatory decisions about the drug, in 2016 and 2021, were sound.

In court filings, the Alliance Defending Freedom, a Christian conservative legal advocacy representing the plaintiffs, has claimed mifepristone is not safe and that the FDA didn't study it closely enough before it was approved.

The group also argued that the FDA’s decisions in 2016, lowering the recommended dosage and extending the use from seven weeks through 10 weeks of pregnancy, and in 2021, which permanently lifted the restriction on requiring abortion pills to be dispensed in-person, were unsound.

In January 2022, the FDA went further by allowing retail pharmacies to provide the drug too, either by mail or in person, so long as they meet certain requirements, which the plaintiffs claim violate federal laws that prohibit the distribution of chemical abortion drugs by mail.

The FDA rejects the claims, arguing that mifepristone is safe when used as indicated and directed, and that the pill went through a thorough and comprehensive review before being approved.

Mifepristone is a drug typically used in combination with another drug, misoprostol, to induce an abortion or to help manage an early miscarriage.

The medication works by blocking progesterone, a hormone that the body needs to continue a pregnancy.

This causes the uterine lining to stop thickening and to break down, detaching the embryo. The second drug, misoprostol, taken 24 to 48 hours later, causes the uterus to contract and dilates the cervix, which will expel the embryo.

The FDA authorized mifepristone for medication abortion in September 2000 for up to seven weeks' gestation, which was then in 2016.

However, the World Health Organization says the two drug-regiment can be taken up until the 12-week mark of pregnancy.

Experts say the Supreme Court's decision could result in limits on the drug even in states where abortion is legal. It could restrict the ability to mail abortion medication to patients living in states with bans in effect and require that the drug be provided in-person, as well as change how many weeks into pregnancy the pill could be used.

The case could also have broader consequences for the FDA's regulatory authority over other drugs.

More than half of all abortions in the U.S. are done via medication, according to from the Guttmacher Institute, which supports abortion access, and the utilization of medication abortions has steadily increased over the last two decades.

Medication abortion quickly became the target of multiple lawsuits after the Supreme Court struck down Roe's guarantees to national abortion access.

Last year, U.S. District Judge Matthew Kacsmaryk in Texas issued an unprecedented ruling suspending the FDA's initial approval of the drug (which has been on the market for nearly 25 years) because, he said, the drug was unsafe and its approval process rushed.

Kacsmaryk's order was partially blocked by the 5th U.S. Circuit Court of Appeals, though that court held the FDA acted unlawfully when it eased rules in 2016 and 2021 to allow the pill to be mailed to patients, prescribed by a medical professional and taken later in pregnancy.

The Biden administration then appealed to the U.S. Supreme Court, warning the loss of access would be "damaging for women and healthcare providers" nationwide and defending the FDA's process as supported by science and decades of safe use.

With the hearing wrapped, after about two hours of arguments, the Supreme Court appeared highly skeptical of the challenge to the mifepristone regulations brought by a group of anti-abortion doctors -- suggesting recent steps to ease access to the medication used by millions of American women may be allowed to stand.

At the heart of the case are steps taken by the FDA in 2016 and 2021 to roll back safety measures around the pill, which was first approved for use in 2000.

The plaintiff doctors -- who do not prescribe mifepristone, use mifepristone or otherwise perform abortions -- claim that wider availability of the drug was authorized improperly and has adversely impacted them, forcing them to care for women in emergency rooms suffering complications from the pill, often in violation of their conscience.

While conservative-leaning Justices Samuel Alito and Clarence Thomas were the most sympathetic to the legal challenges, for the most part, the court on Tuesday steered clear of openly second-guessing FDA’s scientific analysis of mifepristone.

A majority of the justices, across the ideological spectrum, expressed doubt during the arguments that the doctors had sufficiently demonstrated legal standing that they had been directly harmed by the FDA’s mifepristone rule changes.

“It makes sense for individual doctors to seek a [conscience] exemption but they already have that,” said liberal-leaning Justice Ketanji Brown Jackson. “What they are asking for here is -- in order to prevent them from ever having to do these kinds of procedures -- that everyone else should be prevented from getting access to that medication. How is that not overbroad?”

That view was echoed by conservative-leaning Justice Neil Gorsuch.

Erin Hawley, the attorney for the doctors, was repeatedly pressed to provide specific examples or testimony from a physician who had been forced to violate his or her conscience in treating a mifepristone patient but she could not do so.

Solicitor General Elizabeth Prelogar, defending the FDA on behalf of the Biden administration, warned of "profound harm" for women and for drug companies working with the FDA should the lower court's restrictions on mifepristone remain.

-ABC News' Lalee Ibssa and Devin Dwyer