The action comes roughly three weeks after a federal magistrate harshly criticized government regulators for their handling of the drug's approval process, calling their actions "politically motivated and scientifically unjustified."
FDA officials said Tuesday that their decision was based on a pending, amended application submitted by the drug's manufacturer, Teva Womens' Health Inc.
It was not, they said, intended to address a recent court order that the FDA make the drug available, over-the-counter, to all customers without age restrictions.
Up until now, the drug was available without a prescription but could be sold only to customers who were 17 or older.
"Research has shown that access to emergency contraceptive products has the potential to further decrease the rate of unintended pregnancies in the United States," said FDA Commissioner
"The data reviewed by the agency demonstrated that women 15 years of age and older were able to understand how Plan B One-Step works, how to use it properly and that it does not prevent the transmission of
The product can be sold in family planning or female health aisles but must carry the following label: "Not for sale to those under 15 years of age. Proof of age required. Not for sale where age cannot be verified." The package will also have a product code that prompts a cashier to request and verify the age of the purchaser.
A customer who cannot provide age verification will be barred from purchasing the drug. An anti-theft security tag will also be placed on the package, according to the FDA.
The decsions is directly at odds with an order issued by U.S. District Judge Edward Korman, of New York. On April 5, Korman ruled that all levonorgestrel-based contraceptives, such as Plan B One-Step, be made available to all ages, without a prescription, in 30 days' time.
That ruling was the result of a lawsuit brought by the Center for Reproductive Rights, which complained that federal regulators were unfairly limiting access to a safe drug.
On Tuesday, the plaintiff said the FDA was still ignoring "clear and challenging barriers" for women seeking emergency birth control.
"The FDA is under a federal court order that makes it crystal clear that emergency contraception must be made available over the counter, without restriction to women of all ages by next Monday," read a statement from Nancy Northup, president of the reproductive rights group.
"Lowering the age restriction to 15 for over-the-counter access to Plan B One-Step may reduce delays for some young women — but it does nothing to address the significant barriers that far too many women of all ages will still find if they arrive at the drugstore without identification or after the pharmacy gates have been closed for the night or weekend."
The drug, a synthetic hormone, prevents pregnancy by blocking ovulation and impeding the mobility of sperm. It does not cause an abortion in women who are already pregnant, nor does it harm a developing fetus.
The pills are most effective when taken immediately after intercourse and preferably within 24 hours, although they are sometimes effective even after 72 hours.
Critics have argued that easy access to the drug would encourage sexual activity and promote the spread of sexually transmitted infections.