It should be obvious that the dose of medication that works in one person doesn’t work in all people. So it shouldn’t have been a surprise for women this morning to learn that an emergency contraceptive pill identical to the one sold here in the US as Plan B will carry a new warning label in Europe cautioning women that it doesn’t work if they weigh too much.

If they weigh “too much” according to whom? Well, according to the pill dosage. A study in 2011 showed that obese women were three times more likely than thinner women to become pregnant in spite of a dose of emergency contraceptives. The odds of becoming pregnant were higher in obese women who took levonorgestrel compared to other emergency contraceptive pills, prompting this new warning.

The new warning label for a European version of levonorgestrel, Norlevo, now carries a warning that it is less effective for women weighing 75 kilograms (165 pounds) or more and not at all effective for women who weigh 80 kg (176 pounds) or more.

The thing is, the average weight of American women is around 166 pounds. Here in the United States, levonorgestrel is sold as Plan B One-Step, and is the only emergency contraceptive available without a prescription.

Well, can’t you just raise the dose for larger people? Nope. “A dose increase of levonorgestrel is not proven to be a solution for this problem,” explained a spokesperson for HRA Pharma, the company that manufactures Norlevo. The company recommends a copper intrauterine device be used instead for obese women: that acts to prevent a fertilized egg from implanting in the short term, and also serves as long-term birth control. However, they aren’t exactly available for fifty bucks over the counter at three in the morning.

New Warning: Morning-After Pill Doesn’t Work for Women Over 176 Pounds [Mother Jones]
Can we identify women at risk of pregnancy despite using emergency contraception? Data from randomized trials of ulipristal acetate and levonorgestrel. [Contraception]

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