Medical Examiner

The Truth About Whether Plan B Works if You’re Over 155 Pounds

What the research can, and cannot, tell us.

A bunch of birth control options: a condom, emergency contraception, birth control pills.
Photo by Reproductive Health Supplies Coalition on Unsplash

Now that the Supreme Court’s plans for abortion rights are in plain view, the directive for much of uterus-having America seems to be: If you don’t want to be pregnant, don’t get pregnant.

One crucial tool in preventing an egg from becoming fertilized should plan A fail is, of course, Plan B. Following the opinion leak that signaled the potentially looming end of Roe v. Wade, a familiar—or maybe extremely shocking—line about emergency contraceptives has circulated on social media: that the most widely available form of emergency contraception doesn’t work if you’re above a certain weight.

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What!

This is somewhat accurate, though not entirely. (In fact, even the original poster acknowledges as much, lower in a thread. No one retweets the things lower in the thread.) Yes, it is true that the health care system is failing fat people in particular on the emergency-contraceptive front. But the expert consensus is that if you have unprotected sex, it may be worth trying Plan B or another pill, Jen Gunter, an OB-GYN and author of a newsletter called the Vajenda, told me. That is, if you aren’t up for a more extreme emergency contraceptive option.

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The official line from the American College of Obstetricians and Gynecologists is that “body weight influences the effectiveness of oral emergency contraception,” but that it should be offered to folks who are obese or overweight, according to their body mass index, nonetheless.  The key word in that sentence is influences.

There is no perfect BMI cutoff established for emergency contraception’s effectiveness, in part because studies have focused on how participants with several broadly defined BMI groups—“normal,” “underweight,” or “obese”—respond to the medication. As a result, the information researchers have on body weight and emergency contraception is based on zoomed out trends that may or may not apply to any given individual’s body. It’s also worth noting that the available information comes both in the form of how weight affects birth control’s effectiveness, and how BMI—which is slightly different from weight—affects it, making the overall message a little muddled for individuals.

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The fact is that the research into emergency contraception/weight/BMI is a bit sparse. A piece in Self by health reporter Sarah Jacoby from a few years ago walks through the evidence that we do have, which starts with a 2011 study. That work identified a negative correlation between BMI and the effectiveness of Plan B and another pill, Ella. For folks above a BMI of 25, Plan B’s effectiveness appeared to drop off; with Ella, the more dramatic drop-off occurred at a BMI of 30. (Though again: These are broad-brush categories.) Jacoby notes that the Food and Drug Administration did in 2016 consider putting a label on Plan B to explain that its effectiveness decreases with weight but decided against it because the data are “conflicting and too limited.”

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The literature on weight and contraception hasn’t seen much of an update in the years since, says Alison Edelman, an OB-GYN at Oregon Health and Science University and the author of some of that limited research. While she agreed that the issue was nuanced—it’s not that Plan B doesn’t work after a certain weight, per se—she did take a stronger stance than the FDA, explaining that weight “is a risk factor for emergency contraception failure.” Or, to put it more bluntly, if you’re overweight and take Plan B, “I wouldn’t count on it working.” Ella might be a better choice, both she and Gunter noted, for people over 155 pounds, though that pill is prescription-only, and the common thinking among experts is that the effectiveness falls off at about 190 pounds. Edelman has a forthcoming study looking at how the ovary might respond to a double dose of Plan B. The results aren’t available to share with the public, says Edelman, but “I don’t think [they’re] going to change formal clinical recommendations, I’ll say that much.”

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[Read: The Most Unexpected Consequence of the Texas Abortion Ban]

What the official guidance does say right now is that if you have a BMI of over 30, you should be offered an ASAP implementation of a copper IUD, which, according to Planned Parenthood, “lowers your chances of getting pregnant by more than 99.9 percent if you get it put in within 5 days of unprotected sex.” Respectfully, the idea of getting an emergency copper IUD, as a broadly workable protocol, is batshit. IUDs can hurt like hell, can be expensive, and also, copper IUDs in particular may alter your period for the worse; getting an IUD installed (and it really is an installation) is not a choice I could ever imagine making on the fly.

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The reality is that the pill forms of emergency contraception simply are not going to work all the time, no matter your weight. Plan B works by delaying the release of an egg; if the egg is already out and about, it’s too late. Ultimately, “​having access to emergency contraception is vital, but is not the whole piece of the puzzle by any means,” says Edelman. The other pieces being things like access to regular birth control in the first place, sex that is not just consensual but involves cooperation with said birth control, and the option to remove an embryo that has managed to implant in your body, perhaps despite your very best efforts. Aka abortion.

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