Is Plan B Really Less Effective If You're Overweight?

Photo: Megan Madden / Refinery29 for Getty Images

Plan B, aka the morning-after pill, is meant to be there for you in those "oh shoot" moments. Whether you're saying to yourself "oh shoot, the condom broke" or "oh shoot, I forgot to take my birth control," nobody's perfect. So it's always comforting to know that emergency contraception like Plan B is an option. However, there's a not-so-comforting detail about Plan B that isn't exactly common knowledge but totally should be: Apparently, research shows that the effectiveness of Plan B may depend on your weight.

ICYDK, researchers have been exploring the link between weight and Plan B for years, but the subject is making waves now thanks to a new show on Hulu called Shrill, starring comedian Aidy Bryant. (Related: Aidy Bryant Says Her Life Changed When She Stopped Trying to Lose Weight) In the first episode of the show, Bryant's character Annie takes Plan B after having unprotected sex with a guy. One missed period and a positive pregnancy test later, Annie realizes that her Plan B dose didn't work, and she returns to the pharmacy to demand answers. The pharmacist tells her that if she weighs more than 175 pounds, Plan B is less effective.

Cue a collective jaw-drop heard round the world.

If you're wondering "how?!" and "why?!" you're not alone. But to better explain, let's backtrack for a moment. What exactly is Plan B?According to the product's website,  Plan B One-Step is a form of over-the-counter emergency contraception that's meant to be used as a "backup plan" to help prevent pregnancy. You take the pill within 72 hours (though the manufacturer instructions say the sooner, the better) of having unprotected sex or experiencing birth control failure, and that's it-you're (hopefully) protected from an unplanned pregnancy.

Plan B works the way it does because of a hormone called levonorgestrel, and that's where the possible connection to weight comes into play. A handful of studies have suggested that emergency contraception that contains high doses of levonorgestrel may not be as effective for women who fall under the category of obese on the BMI scale (a BMI of 30 or higher). One such study, published in the reproductive medicine journal Contraception back in 2015, collected data from two randomized trials that included more than 1,700 women who'd taken emergency contraception with levonorgestrel. The results showed that "women for whom levonorgestrel was not effective in preventing pregnancy had a significantly higher mean body weight and BMI than women who did not become pregnant." Translation: The higher a woman's body weight and BMI, the more likely it was that emergency contraception containing levonorgestrel would fail to prevent pregnancy. Contraception also published a review of four studies on the subject in 2016, and the researchers wrote that their findings seemed to suggest a correlation between obesity and an increased risk of pregnancy after taking emergency contraception with levonorgestrel, though they noted that they felt that their evidence was "limited" and "poor to fair quality."

Since the research on the connection between weight and Plan B is pretty limited and relatively inconclusive, not to mention the storyline in Shrill was low-key terrifying, we reached out to a couple of experts to learn more.It's important to remember that emergency contraception like Plan B is, at its core, a dose of hormones, and hormones are fat-soluble, "which is exactly why some studies show that emergency contraception may be less effective in women who are overweight (body mass index [BMI] 25–29.9) or obese," says Hedieh Asadi, M.D., cofounder of DeoDoc Intimate Skincare. "Body weight might influence the effectiveness of oral emergency contraception, but it is not possible to draw any accurate conclusions that there is a lesser effect-oral emergency contraception should not be withheld from women who are overweight or obese."

The FDA seems to agree with this perspective, as the agency reviewed the research back in 2016 and decided that the available evidence wasn't strong enough to warrant any changes in Plan B's safety or efficacy labeling. "The FDA continues to believe all women, regardless of how much they weigh, can use these products to prevent unintended pregnancy following unprotected sexual intercourse or contraceptive failure," the agency wrote in a consumer Q&A post back then. And yet, in 2013 in Europe, when manufacturers of an identical version of Plan B reviewed the research themselves, they came to a different conclusion and changed their labeling information to include a warning about weight limitations, reports Mother Jones. So, what's a girl to believe?!

If you're thinking that doubling up on Plan B doses might be a good "just in case" strategy, Dr. Asadi says it's probably best not to go that route. "The best advice to increase the effectiveness is taking the emergency contraception as soon as possible," she says. "The sooner you take the pill, the less the risk of becoming pregnant. No data or scientific studies exist to condone increasing the dose of the emergency contraception pill in relation to weight."

As for regular birth control, even if it contains a dose of the levonorgestrel hormone found in Plan B, there's no need to panic about its effectiveness, as "there is no risk of impaired efficacy of hormonal contraceptives in obese women," says Dr. Asadi. However, she recommends women with a BMI greater than 30 use a nonhormonal IUD instead of hormonal contraceptives, as the latter may "increase the risk of thrombosis (blood clots)," she explains.

Bottom line: The relationship between weight and the effectiveness of Plan B is, at best, pretty complicated. There's no definitive answer as to whether there really are weight limitations associated with the drug, which is no doubt frustrating for anyone who wants (no, needs) to feel confident relying on the emergency contraception in those "oh shoot" moments.

This could point to a larger problem in the medical community-specifically, how health care providers address the issue of weight with their patients, says board-certified ob-gyn Heather Bartos, M.D. "Providers are likely trying to be sensitive to women who get upset when their weight is addressed (I've had patients get very upset that we even bring it up)," says Dr. Bartos. "This does point to the issue of increasing obesity in the United States and how we address this calmly, logically, and without prejudice to patients. It's part of a larger conversation about openness and honesty in the doctor's visit (on both sides of the exam table)."

As frustrating as it is that there's no clear-cut answer about whether legitimate weight limitations really do exist for Plan B,the best thing you can do is tell your doctor that you're confused about this issue. Voice your concerns openly when you have the opportunity to do so, because any health question or concern is completely valid. If nothing else, Shrill's storyline about Plan B keeps an important conversation about emergency contraception in the forefront of your mind, and it encourages you to keep asking questions in the name of your health.