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Effectiveness

Are emergency contraceptive pills effective for overweight or obese women?

Maybe. All emergency contraceptive pills, regardless of type, appear to be significantly less effective for obese women. This is an important consideration in the United States, where over 35% of adults are obese.

In clinical trials of women using EC pills (progestin-only, such as Plan B One-Step or Next Choice, or ulipristal acetate, such as ella) obese women (with a body mass index, or BMI, of 30 or greater) became pregnant over 3 times more often than non-obese women. However, ulipristal acetate (ella) may be more effective for overweight or obese women than progestin-only EC (Plan B One-Step, Next Choice). EC appears to decline in efficacy as BMI increases; in fact, for women with a BMI of 26 or over who used progestin-only EC, pregnancy rates were no different than would be expected if they hadn't used EC at all. Ulipristal acetate (ella) appeared to lose effectiveness at a higher BMI threshold of 35.1, 2 Some new evidence3 is emerging that may support doubling the dose of progestin-only EC for obese women, but it's not certain whether it would be effective.

The most effective choice for emergency contraception for overweight or obese women is the copper IUD. The effectiveness of the copper IUD used as EC is greater than 99%, no matter how much you weigh (and it provides at least 10 years of excellent ongoing contraception).

Click here to calculate your BMI. If your BMI is 26 or greater, consider calling your healthcare provider to get a copper IUD or ella. If you can't get an IUD or ella within 5 days of unprotected sex, but you can get progestin-only EC (like Plan B One-Step or Next Choice), take it as soon as possible. In the US, you can get Plan B One-Step without a prescription, no matter how old you are. You can order ella online for $67 including next-day shipping.

1 Glasier A, Cameron ST, Blithe D, Scherrer B, Mathe H, Levy D, Gainer E, Ulmann A. Can we identify women at risk of pregnancy despite using emergency contraception? Data from randomized trials of ulipristal acetate and levonorgestrel. Contraception. 2011;84:363-7.

2 Moreau C, Trussell J. Results from pooled Phase III studies of ulipristal acetate for emergency contraception. Contraception. 2012;86:673-680.

3 Edelman A, Cherala G, Blue S, Erikson D, Jensen J. Impact of obesity on the pharmacokinetics of levonorgestrel-based emergency contraception: single and double dosing. Contraception. 2016 ;94:52-57.

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