Plan B gets new label by FDA to clarify it doesn't cause abortion

After more than two decades on the market, the emergency contraception drug Plan B One-Step will get a new label by federal regulators to make clear that the pills work by preventing ovulation and do not cause an abortion or impact implantation of a fertilized egg, the Food and Drug Administration announced Friday.

The surprise regulatory move ahead of a holiday weekend is aimed at clearing up confusion on how the drug works. Some pharmacists have cited religious objections tied to abortion in declining to sell the drug, while lawmakers in conservative states have raised the prospect of restricting access or banning it entirely.

The debate has become particularly urgent following the Supreme Court's decision to overturn Roe v. Wade. In his concurring opinion, conservative Justice Clarence Thomas questioned whether state legislatures also should be given more power to decide access to birth control.

The labeling change came as the result of a request by the manufacturer and would apply to generic versions of the drug, according to the FDA.

"Plan B One-Step will not work if a person is already pregnant, meaning it will not affect an existing pregnancy," the FDA now states in an update online. "Plan B One-Step prevents pregnancy by acting on ovulation, which occurs well before implantation. Evidence does not support that the drug affects implantation or maintenance of a pregnancy after implantation, therefore it does not terminate a pregnancy."

Sometimes known as the "morning-after pill," Plan B was approved in the late 1990s to prevent pregnancy. The pills are considered a backup option and must be taken within three days after unprotected sex or if another form of birth control fails, such as a broken condom. The pills are available in pharmacies and online without a prescription, although some pharmacies keep the drug behind the counter.

The drug was never considered by the FDA or medical community as an abortion pill because it only works to prevent, not end, a pregnancy once a fertilized egg is implanted.

When the drug first hit the market, the FDA noted it primarily worked much like other birth control pills by stopping the release of an egg from the ovary. But regulators speculated at the time there was a chance it also might prevent sperm from fertilizing an egg or prevent a fertilized egg from attaching to the womb.

It was this possibility of discarding a fertilized egg -- cited on the drug label and later on the FDA website -- that put the drug in the crosshairs of the conservative movement, with some right-leaning advocacy groups labeling it an "abortifacient" despite objections from the medical community.

Susan Wood, the former director of the FDA's Office of Women's Health, told ABC News this week more recent studies have shown that the drug doesn't impact a fertilized egg. With more data on people who have taken it "at certain stages of their reproductive cycle," she said, it "turns out it only works taken before ovulation."

"If you take it after ovulation, it doesn't work," she said.

Wood, now a professor at George Washington University, said the decision likely didn't come sooner from the FDA because it wasn't necessary from a medical standpoint. There weren't safety issues with the drug, and any agency review of a drug diverts resources away from staff reviewing other drugs. Drug makers also have to request a label change.

In the end, the FDA move will hopefully settle confusion, she said.

"It takes Plan B out of the line of fire for attacks against contraception," Wood said.

ABC's Sony Salzman contributed to this report.