MELISSA BLOCK, HOST:
Even while the Supreme Court takes up the issue of birth control, it appears the most popular form of the emergency contraceptive pill might not work for a majority of American women. NPR's Julie Rovner reports on new research that shows the product loses its effectiveness for women over a certain weight.
JULIE ROVNER, BYLINE: Levonorgestrel is the active ingredient in the emergency contraceptive Plan B and its generic copies. The realization that it starts to lose effectiveness in women who weigh more than 165 pounds came as part of a broader analysis of several different products. Diana Blithe is a contraceptive researcher at the National Institutes of Health and one of the authors of the study.
DIANA BLITHE: When they had enough data from women who had a broad span of weights, from very low weight to very high weight, they found that the levo products became less effective in the higher weight women.
ROVNER: And when weight goes above roughly 175 pounds, regardless of whether women are overweight, obese or just tall, the product basically fails to prevent pregnancy at all. Linda Prine, who practices family medicine in New York City and represents the Reproductive Health Access Project, says the point where effectiveness is compromised came as a stunning realization for most of the product's target population.
LINDA PRINE: This is barely overweight. We're talking about a BMI over 25. So this is probably more than half of American women. This medication would not work for them.
ROVNER: The study found that a newer emergency contraceptive, called Ella, seemed to work better in women who weighed more, although it, too, lost effectiveness as weight went up. The only method that was unaffected by weight was a copper IUD, or intrauterine device, which Prine says does double duty. When used as an emergency contraceptive, it works for five days.
PRINE: It prevents pregnancy at the moment and then it gives them ongoing contraception.
ROVNER: But in addition to being the most expensive, the IUD is controversial. It can prevent the implantation of a fertilized egg. Some people consider that a very early abortion. Many people think that emergency contraceptive pills do that, too, but contraceptive researcher Diana Blithe says recent studies strongly suggest that's not the case, that the pills merely prevent ovulation and, thus, fertilization. And if the FDA is going to require the makers of emergency contraceptives to change their labels to reflect the new information about weight, it might want to give people a better idea about how the drugs work.
BLITHE: This would be a wonderful time to update the label in view of the new science that's very convincing that the levonorgestrel products do not interfere with implantation in any way. And so it would be a really good time to just update the label to reflect the new science that's come out in the last 10 years.
ROVNER: Indeed, that's pretty much what just happened in Europe. According to a document obtained by Mother Jones magazine, the new patient leaflet for the European version of Plan B warns women about weight limitations and it has new language that says, quote, "Emergency contraception pills act by blocking or delaying ovulation following sexual intercourse. They are not effective if ovulation has already occurred." In other words, the pill doesn't cause early abortion because studies suggest that's another case where it just doesn't work. Julie Rovner, NPR News, Washington. Transcript provided by NPR, Copyright NPR.