By Stephanie Stahl

By Stephanie Stahl

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PHILADELPHIA (CBS)–New concerns about the effectiveness of the morning-after pill for women who are overweight.  3 On Your Side Health Reporter Stephanie Stahl has the latest.

The FDA tells 3 On Your Side it is now considering a label change for the U.S. morning-after pill.  This comes after its European counterpart announced the product doesn’t work for certain women.

Concerned patients were calling to figure out if there’s an emergency with Plan B One Step, an emergency contraception.

Another company’s morning-after pill Norlevo, sold in Europe with the same formula, is updating its packaging to warn the product is not effective in women who weigh over 176 pounds.

“It’s important for patients to know that the efficacy is markedly decreased for patients that are heavier,” said Dr. David Ufberg, an OBGYN with Lankenau Medical Center.  He says Plan B One Step has become a popular option for women to prevent a pregnancy after having unprotected sex.

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It’s not clear why the drug stops working in heavier women.  It might have to do with metabolism, or with the volume of the medication in the bloodstream.

New research shows the drug starts to lose effectiveness at 165 pounds.

“If you’re in that higher weight range you need to know that there’s a much higher percentage rate of failure,” said Dr. Ufberg.

While Plan B One Step is the only over-the-counter morning-after pill, there are prescription alternatives.

The Food and Drug Administration says it is reviewing whether the maker of Plan B One Step needs to change its label to reflect the weight warning.

The maker, Teva Pharmaceuticals, tells 3 On Your Side that it’s unable to comment on conversations with the FDA, or the new European label changes because it hasn’t reviewed that  data.

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Stephanie Stahl