Morning after pill less effective for heavier women
New research suggests that some morning-after pills are not as effective at preventing pregnancy in women who weigh 165 pounds, and are not effective at all in women who weigh 176 pounds or more. The European manufacturer of the morning after pill Norvelo is already planning to change labeling next year to include this information.
Norvelo contains a synthetic hormone called levonorgestrel, which is also the main ingredient in Plan B One-Step, the brand name of the morning after pill in the United States. The pill works by delaying or preventing ovulation or blocking the fertilization of an egg, if taken within 72 hours after sex.
The Food and Drug Administration is looking into whether there needs to be a label change for morning after pills in the U.S. The original approval of the drug in the U.S. did not include a weight-related assessment.
Previous studies have shown that hormone-based birth control pills are less effective for heavier women. One study found that obese women taking a levonorgestrel based product were four times as likely as normal weight women to become pregnant.