Plan B, one of the more popular versions of “the morning-after pill” taken after unprotected sex, may not be effective in women above a certain weight – one that happens to be just about the weight of the average American woman.

The good news is, there are other options for women who may now be leery of over-the-counter emergency contraception. But questions remain, such as: Why did it take this long to discover there might be problems with the morning after pill?

Mother Jones reported Monday that French drugmaker HRA Pharma is changing the packaging for its emergency contraceptive Norlevo to warn that it is less effective for women weighing more than 165 pounds and ineffective in women weighing more than 176 pounds. Norlevo, which is sold throughout Canada, Europe, Africa, the Middle East and elsewhere, contains the same dosage of the same active ingredient that’s in the Plan B One-Step sold throughout the U.S. – 1.5 milligrams of the synthetic hormone levonorgestrel. The hormone prevents pregnancy by inhibiting ovulation.

Starting in 2014, new literature included with Norlevo sold in Europe will say, in part, that “studies suggest that Norlevo is less effective in women weighing 75 kg (165 pounds) or more and not effective in women weighing 80 kg (176 pounds) or more.”

The average weight among American women 20 years or older is 166.2 pounds, Mother Jones points out.

Neither Teva Pharmaceuticals, which makes the brand name Plan B One-Step, nor Plan B generic makers Gavis or Actavis have commented on HRA Pharma’s move. No label change proposal has been announced yet for Plan B in the U.S. – and data are lacking on the connections between emergency contraception failure and weight in a pool of American subjects.

The guidance adopted by HRA Pharma makes no mention of a woman’s body-mass index. The 2011 research paper on emergency contraception failure that Mother Jones says first sent HRA Pharma investigating possible label changes did not emphasize weight alone. University of Edinburgh scientists compared data from trials that compared the efficacy of two morning-after pills: levonorgestrel and ulipristal acetate, sold in the U.S. as Ella.

The researchers found that the risk of emergency contraception failure was more than three times greater for obese women (BMI above 30) than women in the “normal” BMI range of 18.5-24.9 with either pill, but was even higher with levonorgestrel. They recommended that overweight women (BMI above 25) opt for an intrauterine device or ulipristal acetate, rather than levonorgestrel.

HRA Pharma reviewed clinical data and asked European pharmaceutical regulators for permission to change the packaging notice – a request granted earlier in November, according to Mother Jones.

So, if a woman is in the weight danger zone and seeking other options, an IUD or an alternative morning-after pill is probably the safer way to go. While levonorgestrel seemed to stop functioning in women with a BMI of 26 or above, a Princeton team’s review of the University of Edinburgh study shows that ulipristal acetate pills like Ella held on until women reached a BMI of 35 [PDF]. Ella does, however, require a prescription, and is shown to have a slightly lower efficacy than Plan B.

IUD insertion is more effective than Ella, but requires a more trying procedure than taking a pill. It also used to rack up hundreds of dollars in copays, but thanks to the Affordable Care Act (Obamacare), most insurance plans have already started completely covering all birth control methods, or will start covering them in 2014.

How did a morning-after pill that’s potentially so ineffective among such a wide swath of patients pass muster? It may be that the clinical trials for Plan B simply excluded women of a certain weight from their trials, as one anonymous physician suggested on Twitter:







Problems stemming from clinical trial subject selection aren’t exactly new. Just recently, researchers discovered that current human papillomavirus vaccines do not target the strains of the virus that are most common among African-American women.