Contraceptive Pearl: Emergency Contraception Considerations for Timing, Weight and Efficacy

Are emergency contraception (EC) pills less effective for overweight patients? Unfortunately, the answer is yes – and the degree of this effect depends on the patient’s body mass index (BMI) and the type of EC.

Levonorgestrel EC (such as Plan B, One-Step and Next Choice) becomes less effective over time following unprotected intercourse. Levonorgestrel EC’s efficacy decreases with high BMI as well. For women with a BMI over 26, levonorgestrel EC is no better than placebo.

Ulipristal Acetate (ella®) EC retains full efficacy up to five days after sexual intercourse. Ulipristal EC has lower efficacy among obese women. Compared with levonorgestrel, ulipristal has a higher BMI threshold. Ulipristal retains its efficacy for women with BMI up to 35.

The copper IUD can be inserted up to five days after unprotected intercourse, reducing the risk of pregnancy by 99%. It retains full efficacy over time and with obesity. Best of all, it provides ongoing contraception for up to 12 years.

When advising your patient on the best type of EC, consider the factors that affect efficacy: time since unprotected intercourse, patient’s BMI, and availability/acceptance of the copper IUD.

We appreciate your feedback! Please write to us at with any questions, comments or additional resources to add to our list.


Helpful Resources

Emergency Contraception: Which EC is Right for Me?

The Emergency Contraception Website 



Glasier A, Cameron ST, Blithe D, et al. Can we identify women at risk of pregnancy despite using emergency contraception? Data from randomized trials of ulipristal acetate and levonorgestrel. Feb 2011, 84(2011): 363-367.  

Moreau C, trussell J. Results from pooled Phase III studies of ulipristal acetate for emergency contraception. May 2012, 86(2012): 673-680. 



The Reproductive Health Access Project does not accept funding from pharmaceutical companies. We do not promote specific brands of medication or contraception. The information in the Contraceptive Pearls is unbiased, based on science alone.

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