Washington DC - America's two biggest pharmacy chains said Friday they will begin dispensing prescription abortion pills in a limited number of states where it's legal.

The move greatly broadens the availability of the drug mifepristone, even as a legal case over whether it was properly approved two decades ago now rests before the Supreme Court.

Walgreens "expects to begin dispensing within a week" in New York, Pennsylvania, Massachusetts, California, and Illinois, the company said on its website.

"But in the interests of pharmacist and patient safety, we will not disclose the number of sites per state nor identify the pharmacies that are dispensing," it added.

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A CVS spokesperson told AFP: "We'll begin filling prescriptions for the medication in Massachusetts and Rhode Island in the weeks ahead and will expand to additional states, where allowed by law, on a rolling basis."

The Food and Drug Administration (FDA) authorized pharmacies to carry mifepristone in January 2023, with Friday's announcements the results of a long certification process.

Mifepristone works to block a pregnancy, while a second drug, misoprostol, provokes bleeding to empty the uterus and was already widely available in pharmacies.

The news was hailed by President Joe Biden, who has made protecting reproductive rights a key part of his re-election campaign against the likely Republican candidate Donald Trump.

Trump tipped the balance of the Supreme Court during his own presidency and paved the way for the reversal of the national right to abortion.

"With major retail pharmacy chains newly certified to dispense medication abortion, many women will soon have the option to pick up their prescription at a local, certified pharmacy – just as they would for any other medication," Biden said in a statement.

"The stakes could not be higher for women across America. In the face of relentless attacks on reproductive freedom by Republican elected officials, Vice President Harris and I will continue to fight to ensure that women can get the health care they need."

The US Supreme Court overturned the nationwide right to abortion in 2022, allowing each state to pass its own laws governing the procedure.

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Twenty-one states have since banned or moved to restrict abortions to limits tighter than before Roe v. Wade, the previous case that upheld the constitutional right to terminate a pregnancy.

Abortion pills remain illegal in states where the procedure is prohibited. But women who decide to travel to a state where abortion is legal may now find a pharmacy much closer than an abortion clinic, reducing their travel.

The Supreme Court will hear arguments on March 26 in a case brought by anti-abortion groups to restrict access to mifepristone, first approved in the year 2000 and used by more than 5.6 million Americans since.