The Food and Drug Administration has approved the availability of the morning-after pill to girls 15 and older without a prescription.
According to the new decision, Plan B One-Step will now be labeled to reflect that proof of age is required to purchase it.
The product will be available in retail outlets with pharmacies.
The pill can also be sold during non-pharmacy hours, too.
The FDA approved Plan B in 1999.
The key ingredient in Plan B is a synthetic hormone called levonorgestrel.
This drug stops an egg from being released from the ovary, or preventing fertilization of the egg by sperm.
If there has been fertilization, Plan B may prevent a fertilized egg from embedding in the uterus. But if the egg has already been implanted in the uterus, the morning-after pill will not work.