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.
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.
Data for the years 2007 to 2010 show the average weight of American women 20 years and older is 166.2 pounds—greater than the weight at which emergency contraceptive pills that use levonorgestrel begin to lose their effectiveness. The average weight of non-Hispanic black women aged 20 to 39 is 186 pounds, well above the weight at which these pills are completely ineffective. A CDC survey published in February found that 5.8 million American women used emergency contraceptive pills from 2006 to 2010.
It is not clear whether drugmakers can formulate an effective levonorgestrel pill for women who weigh more than 165 pounds. "A dose increase of levonorgestrel is not proven to be a solution for this problem," notes Gajek, the HRA Pharma spokeswoman.