A report from Mother Jones indicates that the European manufacturer of a version of the morning after pill will adapt its labels to include a warning that the pill is completely ineffective for women who weigh more than 176 pounds. The pill has a similar chemical composition as a number of American morning after pills, such as Plan B One-Step.

The European manufacturer of an emergency contraceptive pill identical to Plan B, also known as the morning-after pill, will warn women that the drug is completely ineffective for women who weigh more than 176 pounds and begins to lose effectiveness in women who weigh more than 165 pounds. HRA Pharma, the French manufacturer of the European drug, Norlevo, is changing its packaging information to reflect the weight limits. European pharmaceutical regulators approved the change on November 10, but it has not been previously reported.

This development has implications for American women. Some of the most popular emergency contraceptive pills sold over the counter in the United States—including the one-pill drugs Plan B One-Step, Next Choice One Dose, and My Way, and a number of generic two-pill emergency contraceptives—have a dosage and chemical makeup identical to the European drug. Weight data from the Centers for Disease Control and Prevention (CDC) suggests that, at 166 pounds, the average American woman is too heavy to use these pills effectively.

The full report over at Mother Jones includes statistical information the use of the morning after pill in America and different demographics of women who might be more likely to be affected by the new warning. [Mother Jones]