The US Supreme Court appeared sceptical of an effort to restrict access to a commonly used abortion drug, mifepristone, during a Tuesday hearing.

Several members of the court questioned whether it was an appropriate challenge of the drug's federal approval.

It is the most significant abortion case before America's top court since it ended the national right to abortion in June 2022.

The outcome could affect abortion access for millions.

This case centres on decisions made by the Food and Drug Administration, or FDA, to loosen restrictions of mifepristone's use since 2016.

The Alliance for Hippocratic Medicine, an umbrella group of anti-abortion doctors and activists, filed a lawsuit in November 2022 alleging that the drug is unsafe and that the federal agency inappropriately expanded access to it.

Numerous studies have shown that mifepristone, which was first approved by the FDA in 2000, is safe.

But the group, which includes medical professionals, has also argued that its members might suffer harm by having to treat patients who used mifepristone to end a pregnancy. They said that would be in opposition to their own religious beliefs.

Elizabeth Prelogar, the US Solicitor General, told the court that the doctors could not show that the FDA's decisions had directly harmed them.

She added that ruling in favour of the anti-abortion group would "severely disrupt the federal system for developing and approving drugs" and "inflict grave harm on women across the nation."

Several of the judges seemed to find the basis for the case dubious. Even some of the conservative justices who have ruled in favour of anti-abortion plaintiffs in the past questioned whether the doctors had suffered due to the rule changes.

Justice Amy Coney Barrett, who was appointed by former President Donald Trump, pressed the group's attorneys on whether two of the doctors cited in the case had been forced to terminate a pregnancy against their will.

Some of the justices, both liberal and conservative, asked whether there was a "mismatch" between the injuries claimed by the group and the changes they were pursuing - limiting millions of Americans' access to mifepristone.

Justice Neil Gorsuch, another conservative judge appointed by Mr Trump, questioned whether a ruling in their favour could open the door to "a handful of individuals" turning a "small lawsuit into a nationwide legislative assembly on an FDA rule, or any other federal government action".

Two of the court's liberal justices, Justice Elena Kagan and Justice Ketanji Brown Jackson, asked why the doctors were not already protected by their right to lodge conscience objections to certain procedures, like abortion.

Mifepristone is used in combination with another drug - misoprostol - for medical abortions, and it is now the most common way to have an abortion in the US.

Medical abortions accounted for 63% of all abortions in 2023, up from 53% in 2020, according to the Guttmacher Institute. More than five million US women have used mifepristone to terminate their pregnancies.

The court has previously ruled that it would not consider a challenge of the FDA's approval of the drug, but a ruling against the FDA could severely limit access as it would roll back the expansion of access that has occurred since 2016.

The FDA announced in 2016 that it would allow mifepristone's use until the 10-week mark, rather than up to seven weeks of gestation. Then in 2021 it lifted in-person dispensing requirements, a move that allowed providers to send it to patients by mail.

In 2022, the FDA moved further by allowing retail pharmacies to dispense the drug, meaning medical professionals - not just doctors - could prescribe it. The following year, a judge in Texas revoked the FDA's approval of mifepristone.

Abortion remains one of the most contentious political issues in the US, and will likely be a major factor in the 2024 election.

Illustrating that friction, anti-abortion advocates and reproductive rights groups setup lecterns with microphones next to each other at the steps of the Supreme Court. Each side hosted a roster of speakers who called on the justices to "do the right thing", though they called for different outcomes.

In total, a few hundred protesters gathered outside the court on Tuesday. Many waved signs that carried phrases like 'abortion is healthcare', 'trust medical science' and 'we won't go quietly back to the 1950s'.

Thirteen of the protesters were arrested for illegally blocking roads and a walkway, according to the US Capitol Police.