A drug similar to Plan B was recently found to be ineffective in women who weigh more than 176 pounds.

After investigating the pill's effectiveness, European drug manufacturer HRA Pharma plans to put a warning on the drug's label that the drug is not recommended for women who weigh 165 pounds or more, the New York Daily News reported.

An HRA representative told Mother Jones that the company looked into the drug's effectiveness after a 2011 study revealed that levonorgestrel, the active ingredient, tended to fail in women with a higher BMI.

The new warning label will read "studies suggest that NorLevo is less effective in women weighing (165 pounds) or more and not effective in women weighing (176 pounds) or more" and that NorLevo "is not recommended ... if you weigh (165 pounds) or more."

The finding came after ongoing research from the company, HRA Pharma CEO Erin Gainer told the NY Daily News.

"When we became aware that there appeared to be an impact on efficacy (linked to weight), we felt it was our ethical duty as a drug manufacturer to report it and be transparent," Gainer said.

HRA hasn't made a public announcement in Europe yet, but the company's label change has been approved. The process to put the new warning label into effect will likely take several months, Gainer said.

Plan B One-Step, the American equivalent of the drug, does contain the same 1.5mg dose of levonorgesterol, according to manufacturer Teva Pharmaceuticals. Representatives declined to comment on the drug's effectiveness.

NorLevo and Plan B use levonorgestrel to help prevent pregnancy when taken within 72 hours of unprotected sex. Plan B and generic versions were made available over the counter to women of all ages earlier this year.

If Plan B is found to be ineffective for women with a higher BMI, it could potentially affect millions of American women, the NY Daily News noted.

The average American woman age 20 or older weighs 166.2 pounds, according to the Centers for Disease Control and Prevention.

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