The Food and Drug Administration approved a change in labeling for the Plan B “morning after” pill Friday to clarify it does not prevent a fertilized egg from implanting in the uterus – language that had been cited by abortion opponents to argue the medication causes abortions and should be restricted.

For years, the FDA-approved label for Plan B One-Step and its competitors said the medication works mainly by stopping the release of an egg from the ovary or possibly by preventing fertilization of an egg by sperm. But it also suggested that if an egg is fertilized, the drug may prevent it from attaching to the wall of the uterus.

That was revised on Friday to say “Plan B One-Step works before release of an egg from the ovary. As a result, Plan B One-Step usually stops or delays the release of an egg from the ovary. Plan B One-Step is one tablet that contains a higher dose of levonorgestrel than birth control pills and works in a similar way to prevent pregnancy.”

The change was welcomed as long overdue by abortion rights groups, who worry that antiabortion groups, emboldened by the Supreme Court decision in June to overturn Roe v. Wade, will use misinformation about the morning-after pill to push for restrictions and bans on emergency contraception in state legislatures next year.

“It’s great that the FDA is reflecting the science. But I believe that the folks who are opposed will still keep coming after it,” said Mara Gandal-Powers, director of birth control access and senior counsel at the National Women’s Law Center.

Antiabortion activists and conservative state lawmakers have long cited the label on morning after pills in describing them as “abortifacients” – drugs that can induce abortions. For those who believe that a life begins when an egg is fertilized by a sperm, a drug that prevents implantation is tantamount to killing a human being.

Researchers have long disputed the idea that the pill blocks implantation, however. Emergency contraception is “unlikely to prevent implantation of a fertilized egg,” according to the website of the American College of Obstetricians and Gynecologists.

The website for the antiabortion group Students for Life of America describes Plan B, for instance, as a medication that can create “an inhospitable uterine environment,” preventing implantation by the embryo. If that happens, “he or she will die,” the website says.

But guidance added to the FDA website Friday makes clear the agency does not consider the medication an abortion pill.

“Plan B One-Step will not work if a person is already pregnant, meaning it will not affect an existing pregnancy …,” it wrote. “Evidence does not support that the drug affects implantation or maintenance of a pregnancy after implantation, therefore it does not terminate a pregnancy.”

After the Supreme Court ruling on abortion, demand for the pills soared as women worried that their options for reproductive health were under threat, advocates said.

The commonly-used over-the-counter drug contains levonorgestrel, a synthetic hormone that can prevent pregnancy if taken within 72 hours of unprotected sex. It usually costs between $40 and $50; generic versions cost less. An FDA spokesperson said makers of generic versions have a year to make similar labeling changes.

The morning after pill is different from the abortion pill, mifepristone, which is used with another drug, misoprostol, to terminate a pregnancy less than 10 weeks along.

The label for Plan-B had not changed since 2006, when the drug was switched from a prescription medication to over-the-counter.