Plan B, the emergency contraceptive, may not work for women over a certain weight.
An emergency contraceptive manufactured in Europe will come with a new label next year warning that the pill may not be effective for women over165 pounds. A public health expert at Princeton University says the European drug Norlevo, is identical to the Plan B One-Step sold in the United States.
The French manufacturer of the drug says it discovered that a woman's weight impacts the effectiveness of the drug.
Emergency contraceptives are often called the morning-after pill because they work by interfering with ovulation, preventing the fertilization of an egg.
The Food and Drug Administration "is currently reviewing the available and related scientific information on this issue, including the publication upon which the Norlevo labeling change was based," said spokeswoman Erica Jefferson. "The agency will then determine what, if any, labeling changes to emergency contraceptives are warranted."
Plan B is available in the U.S. to people of any age without a prescription.