If you pick up a box, you'll likely see instructions for how and when to take the medicine, fine print, ingredients, and allergy warnings. But if you're looking for information about weight limits on a box of Plan B, you won't find any. This wouldn't be unusual, except research suggests reduced EC efficacy among people who weigh 155 lbs or more, or have a body-mass index (BMI) over 25. And in 2013, NPR reported that NorLevo, a European EC equivalent, issued a warning to consumers about a lack of efficacy with an increase in BMI numbers.
Nearly 1 in 3 women have a BMI between 25 and 29.9, and 2 in 5 women have a BMI above 30, according to a 2018 survey conducted by the National Health and Nutrition Examination Survey (NHANES). Additionally, a Centers for Disease Control and Prevention (CDC) survey, conducted between 2017-2019, found that 24.3 percent of sexually active women aged 22 to 49 have used emergency contraception. The data did not distinguish beyond the gender binary—but the implications for all people who menstruate can be extrapolated. The NHANES numbers suggest that reduced efficacy may impact 69.4 percent of users and may not work at all for 41.9 percent.
Because these numbers are so startling, we had experts break down precisely what the data means, why the efficacy is reduced, whether it's safe to take Plan B in the face of the weight research—and a few other EC options.
Here's what the research says
The European label change came after a 2011 meta-analysis, published in the journal Contraception, examined two clinical trials that tested the effectiveness of levonorgestrel (i.e., Plan B, My Way, Next Choice, etc.) and a different EC called ulipristal acetate (known as Ella). Researchers found that women with a BMI over 25 have a greater risk of getting pregnant after taking levonorgestrel. They concluded that women who fell into that category should be offered a copper IUD or ulipristal acetate instead.
Other studies have examined decreased efficacy levels among those with higher BMI in the years that followed. A 2015 study, also from Contraception, found that people who weigh above 176 lbs had a 6.4 percent greater chance of getting pregnant, compared to peers weighing below 176 lbs, who had a 1.4 percent chance. The average pregnancy risk percentage with no contraception was 6 percent for the control group in this study.
The United States Food and Drug Administration (FDA) agreed to review the research in 2013. The FDA ultimately concluded that existing data is too limited and conflicting to make a definitive conclusion on exact weight limits and decided that changing the label is unwarranted. Admittedly, there should be larger, more comprehensive studies, wrote Lauren Vogel, Canadian medical journalist, author of a 2015 article published in the Canadian Medical Association Journal. However, she adds, the existing body of research shouldn't be ignored. Additionally, research should target the "why" behind levonorgestrel's reduced efficacy in larger patients.
The FDA says that the most important factor impacting EC efficacy is time: Taking EC within 72 hours of unprotected sex or contraceptive failure yields the best result; however, that window can be extended up to 120 hours, with a lower percentage of effectiveness, says Planned Parenthood. The FAQ section of the Plan B website, states that the manufacturers agree with the FDA and share the aforementioned sentiment. There isn't a definitive weight limit for Plan B or other levonorgestrel-based EC.
So how worried should you be? The literature does suggest a correlation between reduced efficacy and higher BMI; however, Sophia Yen, MD, MPH, co-founder and CEO of Pandia Health, says assertions that EC does not work past a certain weight are an overstatement.
Reduced efficacy isn't a definitive red light, Dr. Yen says. And there isn't any evidence that taking levonorgestrel-based EC is unsafe. So, even though the data is concerning, it doesn't mean that it is guaranteed not to work, Dr. Yen says. The risk of pregnancy is just higher for people with a BMI above 25.
Why is weight a factor for levonorgestrel EC
There are more questions than answers when it comes to the why. Some experts believe that more fat cells might mean that more of the hormone is stored instead of actively preventing conception, says Kate Steinle, NP, chief clinical officer of FOLX Health. Additionally, people with higher BMI may have higher blood volume, potentially impacting efficacy. Steinle also says the drug may be metabolized differently in people with a higher BMI.
Another theory, one posited by Melissa Maples in an article published by Endocrine News, is that the dosage may need to be higher for people of higher weights. However, there isn't enough evidence to make any definitive statements about reduced efficacy.
Are there other EC options available
The good news? There is EC with a higher weight efficacy, says Dr. Yen. Ella is EC that contains ulipristal acetate instead of levonorgestrel and claims effectiveness up to 195lbs or a BMI of 30— and possible efficacy up to 35, according to Planned Parenthood. The downside to this option is it is not over the counter.
Prescription-based EC isn't necessarily the best strategy for something you need in an emergency, especially given the number of people in the U.S. without insurance, a primary care provider, or access to prescription medicine. Ella is typically $50 with a prescription, around $40 with a GoodRx coupon, or free with most insurance plans and Medicaid, according to Planned Parenthood. Because Ella is prescription-based, you could acquire it via a care provider and keep it on hand, Dr. Yen says.
The most effective form of emergency contraction is the copper intrauterine device (IUD) called Paragard. Paragard is inserted during an in-office procedure where the IUD is inserted through the cervix and into the uterus. People usually experience mild to heavy cramping during the procedure. As long as it is inserted within five days of unprotected intercourse, Paragard is 99 percent effective in preventing pregnancy, and BMI has no impact. Additionally, it can act as ongoing birth control for 12 years after insertion (and can be removed at any time).
At the end of the day, when you need to take EC, you've probably got a lot on your mind. The last thing you want is to worry about whether or not medicine will work based on your body size. However, it's essential to know the details and risks so you can make additional reproductive plans.
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