When a federal judge in Texas ruled that the Food and Drug administration shouldn't have approved the abortion pill mifepristone in 2000, he agreed with arguments by plaintiffs who oppose abortion rights in ruling that the agency improperly used a process of accelerated approval that didn't fully assess the drug's risks and benefits..

An appeals court stayed the part of the lower court's decision that would have invalidated the FDA approval, but the matter could ultimately be decided by the Supreme Court.

Outside the courts, there are concerns that the litigation could undermine the agency's authority. And there's skepticism about the claim FDA acted improperly on mifepristone.

"It's just not credible," says Dr. Joshua Sharfstein, a former deputy commissioner for the FDA who is now a vice dean at the Johns Hopkins Bloomberg School of Public Health. "This had the full support of advisory committees. It had the full support of major professional associations, and it retained that support after millions of women have received the treatment."

NPR reviewed approval documents, transcripts and other reports about mifepristone compiled over the years. Here's what we found out.

The FDA wasn't first to approve the abortion pill

Although the FDA's 2000 approval of mifepristone was groundbreaking in the United States, it wasn't such a big deal to other countries. That's because they already had access to mifepristone.

Mifepristone was invented by a French drug company, Roussel Uclaf, in 1980, and won approval in France in 1988.

But the French company suspended distribution that year after threats from groups that oppose abortion rights. It lasted two days before the French health minister – noting that France owned part of the company – ordered it back on the market. He said, "from the moment governmental approval for the drug was granted, [mifepristone] became the moral property of women, not just the property of the drug company." according to a 2001 report by the Congressional Research Service.

The drug was then approved in China, the United Kingdom and Sweden in the late 1980s and early 1990s. Then in 1999, nearly a dozen more countries approved mifepristone.

The U.S. took its time on the approval

Once the Population Council – mifepristone's original sponsor in the U.S. – submitted its FDA application in 1996, some speculated that the approval could happen as soon as 1997. But it didn't.

The FDA convened an advisory committee of outside experts to assess the drug for approval in July 1996. The advisers voted that the drug was safe and effective, but wanted to see more data from an ongoing U.S. study at the time and recommended additional safety restrictions because so much of the data was collected from the French health system, which is very different from the U.S. health system. .

The FDA went through three rounds of reviews over four years, each time issuing an "approvable" letter, meaning the safety and efficacy data was solid. But the agency asked for details about manufacturing and the instructions for the drug before ultimately approving it in September 2000.

The agency's medical review mentions dozens of studies done mostly in France, including one that had 16,000 participants.

The approval relied on two pivotal French studies and one U.S. study with similar safety and efficacy findings.

The FDA regulation has multiple parts

The anti-abortion rights groups that sued the FDA have stated incorrectly that mifepristone got what is known as an "accelerated approval."

While it's true that some details of the mifepristone approval were handled under a section of FDA regulation called Subpart H that also covers accelerated approvals, that part was not invoked.

The part the agency used in the approval allowed it to add safety restrictions, such as requiring that physicians providing the pill be able to diagnose ectopic pregnancies.

When the agency grants an accelerated approval, it uses preliminary data, and the drugmaker has to do follow-up studies to confirm the medicine really works. The FDA didn't do that with mifepristone.

The lawsuit incorrectly argues that the FDA used accelerated approval. Judge Matthew Kacsmaryk also cites accelerated approval in his ruling. The FDA did not use that part of the law in its process, however.

Mifepristone's approval has been questioned before

This isn't the first time there have been allegations that the FDA bungled the approval of mifepristone, which was known as RU-486 early on.

For example, there was a House hearing about mifepristone in 2006.

"There are people who have wanted RU-486 to be pulled off the market since the day it was approved," then-Rep. Henry Waxman, a Democrat from California, said at the time. "In fact, they didn't want it to be approved. I respect their judgment because they are very strongly against an abortion, whether it be by RU-486 or by a medical procedure. But that is not the issue of safety and it is not an issue of science and it is not an issue of data."

Republican senators requested a Government Accountability Office review of the approval that was published in 2008. Researchers found that mifepristone's approval and oversight were in line with the other eight drugs approved with similar subpart H safety requirements.

"If there is a problem with this medicine then there's a problem with many, many other medicines," Sharfstein says. "Because this is very much in line with what FDA does and has the full support of the medical community."

Edited by Scott Hensley and Diane Webber.