Several news agencies are reporting that the levonorgestrel morning after pill (marketed both as Plan B and 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 with 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 for 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.