Several news agencies are reporting that the levonorgestrel morning after pill (marketed both as Plan B logo_planbonestepand as a generic in the United States) is ineffective for women who weigh more than 176 lbs. The news reports are based on the fact that HRA Pharma, the French manufacturer of an identical levonorgestrel morning after pill to Plan B, is changing its labeling to indicate that the drug is ineffective in women who weigh more than 176 pounds and less effective in women who weigh 165 or above.

This is not news. It is very important medical information, but it is certainly not new medical information. It is well-known that the risk of failure with oral emergency contraception is more than 3 times greater for a women with a BMI (body mass index) of 30 or greater and 1.5 greater for a woman with a BMI in the overweight range (BMI of 25 to 29.9). The data that I quote comes from a study published in 2011. So, like I said, it’s not new information and why it took a French manufacturer changing its labeling to draw attention to this is an entirely separate story. 

We know that the risk of failure based on BMI is greater for levonorgestrel methods (such as Plan B) than imageswith Ella (ulipristal acetate or UPA). For obese women taking a levonorgestrel method the failure rate is more than 4 fold higher compared with women who have a BMI < 25. It is likely that for women with a BMI of 30 or more that levonorgestrel to provides little if any benefit. For UPA users the risk of failure is more than double for obese women, so not as bad as a levonorgestrel method and likely more effective than taking nothing.  

Several studies have evaluated the link between obesity and oral hormonal contraception efficacy.  There is definitely a concern that BMI (which provides a better estimate of body fat versus actual weight) may have an effect, although sadly this is really understudied.  BMI is likely a better a better tool as the efficacy of hormones for contraception is probably most affected by fatty tissue as this can act like a drug reservoir, removing active drug from circulation. In addition, obesity changes the levels of certain hormones which may also affect how much active drug is available. However, it’s understudied so the connection is not fully elucidated.  

Without seeing any new data from HRA Pharma (I can’t find any new studies, I suspect they re-evaluated previous data, but that’s just a guess) I use the published data and thus BMI over body weight. Levonorgestrel methods, like Plan B, are significantly less effective for women with a BMI of 30 or more. A copper IUD within 5 days of unprotected intercourse will offer the best method of post coital contraception 090729_medex_iudtnfor women regardless of BMI and for women with a BMI over 30 and Ella is the second choice based on efficacy.  Will Plan B be harmful? Not the drug itself, but the false belief that something can help when it likely doesn’t is a concern as it might prevent a woman from seeking a better option.

This leaves women with a BMI of 30 or more (which is more than one-third of reproductive aged women in the United States) at significantly higher risk for an unplanned pregnancy as the effective methods for this population are not available without a prescription (Ella) or an appointment (copper IUD).

Why the FDA never required information about efficacy and obesity on the packaging for levonorgestrel methods when the data has been around for at least a couple of years (if not longer), well, that’s what I’d like to know? And the Federal Government who were so hell bent on protecting minors from taking the morning after pill? Perhaps if they’d taken time to read the literature and speak with experts maybe they could have pushed for package labeling that might have actually helped many women make a more informed choice.




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  1. It seems to me that by now we should be looking at adjusting the hormone level of the birth control pill and Plan B by body weight. Why isn’t this being done? The cost of research?

    1. Interestingly a higher hormone combination, the Yuzpe method, had a higher failure rate because of vomiting due to the high dose estrogen. I wonder if there is any data looking at that method by BMI? Probably not because it’s from the early 80s, but might be worth a look.

      1. Anna Glasier (Professor of Obstetrics and Gynaecology at Edinburgh University, author of the 2011 study) and Karina Gajek (of HRA Pharma) have both stated that clinical data shows that increasing the dose of levonorgestrel for heavier users has no effect on effectiveness. That probably won’t stop some dishonest company marketing something along the lines of a ‘Plan B Plus’ for people who weigh more.

        It’s a great pity that the US (in general) is so wary of intrauterine devices, and charges so much to fit the two (is it still true that only two are in general use?) types used. At current rates that I’ve been quoted (anecdotally) it’s probably cheaper to take a chance and then have a first trimester abortion, than to have a copper IUD fitted. That’s really ironic in a country so gung-ho about reducing medical and surgical abortion rates, no?

  2. It would be interesting to know why the manufacturer is choosing to re-label by simple weight. (Matches their data better? Ease of determination for the prescriber/seller? No idea.) I am 193cm tall, pure weight guidelines tend to rule me out of things entirely, and conversely for very short women, it may be exposing them to risk.

      1. Why do you think BMI is the factor rather than weight? The bigger the body the less hormone in any given CC of the body. Most drugs aren’t that sensitive but if you’re going for the lowest effective dose that would be a factor unless you’re dealing with something that most of the body ignores.

      2. It’s the fatty tissue. Fat expands the volume of distribution in a way that can lead to a drug being sequestered or stored. We have this problem frequently with patients who have high BMIs. That’s my guess anyway.

  3. Oddly enough, I’m on levonorgestrel/ethinyl estradiol as my birth control method, and in theory it should not work for me. I average 315 lbs, and a few years back my gyn told me oh this might not work for you. We discussed it, and based on previous experimentation with a lower-dose pill, I was able to prove that no, it does work for me. When I was on a lower-dose pill, my period was all over the place – I had four within two months, and two of them had 7 days from end of one bleed to start of the next. This is what I have had happen to me since I first started, but when I’m on BCP, I have perfectly regular schedules.

    It is scary to find out that what you think should work, doesn’t, however. I only trust it works because of the personal evidence I have, and of course that can’t translate to another person perfectly – the difference between my fat solubility, rate of liver metabolizing, and my endocrine system sensitivity, is possibly mine alone. Bodies are wacky things.

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