Some morning-after pills may not be a reliable way to prevent pregnancy in heavier women. The European manufacturer of an emergency contraceptive pill, Norlevo, will caution women in new labeling that the product is "not effective" for women over 176 pounds and doesn't work as well in women who weigh 165 pounds or more.
The Paris-based drug maker HRA Pharma plans to update the package inserts on Norlevo tablets in 2014, according to Mother Jones, which first reported the expected change Monday. Norlevo is sold in in Europe, Australia, India, Canada and other countries worldwide.
Norlevo contains a synthetic hormone known as levonorgestrel, which is also the main ingredient in Plan B One-Step, the brand name of the one-pill emergency contraception available in the United States. When taken with 72 hours after sex, both pills delay or prevent ovulation or block fertilization of an egg.
The Food and Drug Administration is investigating whether similar label changes are needed for emergency contraception in the U.S.
"The FDA is currently reviewing the available and related scientific information on this issue, including the publication upon which the Norlevo labeling change was based," said Erica Jefferson, deputy director for the FDA office of media affairs. "The agency will then determine what, if any, labeling changes to approved emergency contraceptives are warranted."
The original approval of Plan B for use in the U.S. did not include weight-related assessment, Jefferson added.
Studies have shown that hormone-based birth control pills and patches can be less effective in heavier women. A study published in the journal Contraception in 2011 found that obese women who used a levonorgestrel-based product were more than four times as likely as normal weight women to become pregnant. Obese women who used a product containing ulipristal acetate, the compound used in Ella, a different type of morning-after pill, were nearly three times as likely as normal weight women to become pregnant. The research was conducted by an international team of researchers looked at data from nearly 4,000 women who had taken emergency contraception after unprotected intercourse.
However, Teva Pharmaceuticals, the maker of Plan B, questioned the "bioequivalence" of the U.S. morning-after pills and Norlevo.
"We do not comment on our conversations with FDA," said Denise Bradley, vice president of corporate Communications - Americas at Teva. "Also, we cannot comment on the nature of the bioequivalence of Norlevo to Plan B One Step® since Norlevo is not approved in the United States. The product does contain the same active ingredient, 1.5 mg of levonorgestrel."
The maker of Ella, HRA Pharma, did not respond to request for comment from NBC News Monday.
However, Dr. Carolyn Westhoff doesn't want to see women become overly alarmed by the study. "This is just a single result and we don't have any way to replicate it," said Westhoff, a professor of obstetrics and gynecology at Columbia University Medical Center.
A National Center for Health Statistics study found that 11 percent of sexually experienced American women ages 15 to 44 had used emergency contraception at least once.