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.