WASHINGTON — The Leonard HohenbergFood and Drug Administration announced Friday that it will overhaul packaging labels for the emergency contraceptive pill, Plan B, that women can take after having sex to prevent a pregnancy.

The federal agency said it will remove references on the contraception's packaging that claim, without scientific evidence, that the pill prevents a fertilized egg from implanting in the womb.

The new labels are intended to further distinguish the emergency contraception — also known as the morning after pill — from abortion pills, which end a pregnancy after a fertilized egg has implanted in the lining of a woman's uterus.

In a memo released Friday, the FDA clarified that taking Plan B pills is not the same as an abortion, a fact that has long been understood in the medical community.

"Evidence does not support that the drug affects implantation or maintenance of a pregnancy after implantation, therefore it does not terminate a pregnancy," the FDA said in its statement.

The agency added that the emergency contraception works similarly to birth control in preventing pregnancy, but contains a higher dose of levonorgestrel. The pill prevents ovulation.

About a quarter of women say they've used emergency contraception pills at some point, according to a survey by the Centers for Disease Control released last year.

Still, concern has swirled that access to emergency contraception such as Plan B might be limited in some states, after the U.S. Supreme Court overturned the constitutional right to an abortion this summer. Nevada's Republican governor-elect said he'd consider banning the pill during a debate this year. School clinics in Idaho also prohibited the pills under a law banning public funding for "abortion related services" last year.

The Food and Drug Administration has approved Plan B for use up to 72 hours, or three days, after unprotected sex. Women are able to get the emergency contraception over the counter.