Does body weight change the effectiveness of birth control?

Taking a patient-centered approach to talking about body weight and birth control effectiveness.

by Robin Watkins, CNM, WHNP-BC

published 02/14/24

Depending on your patient’s body weight and the method of birth control they are using, the effectiveness of their method at preventing pregnancy might be impacted. Additionally, some medications and surgeries used for weight loss can impact birth control effectiveness. With more and more patients using these treatments, we’ve got you covered with what providers need to know.

Talking to patients about body weight and birth control

Before we get into the details, it’s important to ensure you offer counseling in ways that keep your patient at the center of the conversation. Weight bias in health care is real and providers should prioritize building and maintaining rapport with their patients. Rapport is a key component of providing high-quality, patient-centered contraceptive counseling and foundational to any conversation about contraceptive effectiveness and body weight. In addition to how you talk to patients about body weight, providers should consider ways to ensure their care and clinic spaces are welcoming to people of all body sizes, such as considering the weight capacity of exam tables and ensuring supplies needed for method initiation are available in appropriate sizes.

What birth control methods are less effective based on body weight?

EC pills

The effectiveness of emergency contraceptive (EC) pills, both over-the-counter and prescription ones, is impacted by increasing body weight. The best available evidence suggests that over-the-counter, levonorgestrel (LNG) EC (Plan B and generics) may be less effective for people who weigh 165 pounds or more, and ineffective for those weighing 176 pounds or more. Studies have also found that prescription, ulipristal acetate EC (ella) may be ineffective for people who weigh 196 pounds or more. We do know that weight doesn’t change how effective IUDs are for EC—about 100% effective. We’ve also got you covered with how to talk to your patients about EC.

You might have heard that taking two over-the-counter LNG EC pills would increase the effectiveness of over-the-counter EC pills for people who weigh over 165 pounds, but unfortunately, research shows that it doesn’t.


The effectiveness of all birth control patches on the market in the US—Xulane, Zafemy, and Twirla—is impacted by body weight. Xulane and Zafemy contain the same hormones and are likely to be less effective for people who weigh more than 198 pounds. This doesn’t mean that the patch will completely stop working when someone weighs 199 pounds, so providers should use a patient-centered approach to counseling patients about potentially decreased effectiveness with increasing body weight.

For the lower-dose patch, Twirla, researchers found that Twirla was less effective at preventing pregnancy for people who have a BMI of 25 kg/m2 or greater. Twirla isn’t recommended for people with a BMI is 30 kg/m 2 or greater because of decreased effectiveness and a potentially increased risk of blood clots.

What about other methods?

All other methods, including IUDs, the implant, shot, ring, birth control pills, and barrier methods, like condoms, internal condoms, and diaphragm, as well as sterilization have been shown to be equally effective for people across all body weights.

Does weight loss surgery change how effective birth control is?

There are several different approaches and techniques for weight loss surgeries, also known as bariatric surgeries. Bariatric surgery can be either restrictive, such as sleeve gastrectomy or gastric banding, which decrease the size of the stomach and the amount of food needed to feel full, or malabsorptive, such as gastric bypass, which makes the stomach smaller and rearranges part of the small intestine to change the way the body absorbs food. Because gastric bypass impacts the way food is absorbed it also impacts how oral medications are absorbed. This means that oral birth control pills, including combination and progestin-only pills, are less effective for people who have had gastric bypass surgery.

What about medications used for weight loss?

Patients are increasingly using GLP-1 agonist medications, such as tirzepatide (Mounjaro), semaglutide (Wegovy, Ozempic), and dulaglutide (Trulicity), to manage type 2 diabetes as well as for weight loss. One of the ways these medications work is by slowing digestion, this means that it can impact how oral medications, including birth control pills, are absorbed and may impact how effective they are at preventing pregnancy. Tirzepatide (Mounjaro) comes with a warning that people who take birth control pills, including combination and progestin-only pills, should use a backup method of birth control for four weeks after starting and for four weeks after a dosage increase.

Bottom line

When counseling about birth control and body weight, providers should prioritize building rapport and offering patient-centered counseling. While some birth control methods may be less effective for people with higher body weights, for those who have had gastric bypass surgery, or for those using medications increasingly used for weight loss, there are birth control methods that are equally effective for people of all body weights. Additionally, body weight is not an absolute contraindication for the use of any birth control method, so providers should use informed decision-making in contraceptive counseling about body weight and birth control effectiveness.

Robin Watkins is the Director of Clinical Affairs and Medical Education at the Society of Family Planning. Robin is a midwife and women’s health nurse practitioner focused on expanding provider capacity to offer just, equitable, resonant, and high-quality sexual and reproductive health care. Robin provides clinical care in the Washington, DC area. When she is not talking sex or placing IUDs, you can find her riding her bike on the streets of DC or eating ice cream for dinner.
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