Emergency Contraceptive Pill Efficacy and BMI/Body Weight


Analysis of data from the two randomized trials of the ulipristal acetate (UPA) and levonorgestrel (LNg) regimens[1], 2] found that when compared with women who were not obese, obese women taking LNg had a significantly higher risk of pregnancy whereas women taking UPA did not. LNg showed a rapid decrease of efficacy with increasing body mass index (BMI), reaching the point where it appeared no different from pregnancy rates expected among women not using EC at a BMI of 26 compared with a BMI of 35 for UPA.[3] The manufacturer of NorLevo (a 1.5 mg LNg) requested a change to the product label to reflect the findings from further analyses of these data. In November 2013, European regulatory authorities approved a label change to include the following: “In clinical trials, contraceptive efficacy was reduced in women weighing 75 kg or more and levonorgestrel was not effective in women who weighed more than 80 kg [176 lbs].”[4] However, the European Medicines Agency, after reviewing additional data from three WHO trials[5],[6],[7] that did not find reduced efficacy with increasing weight or BMI, removed that statement from the Norlevo label in July 2014.[8] These trials were not specifically designed to study the relationship between efficacy and weight, and ascertainment of both weight and pregnancy were based on self-report in some of the studies. The effect of weight on the efficacy of combined emergency contraceptive pills (ECPs) has not been studied.

There is no conclusive answer about the precise relationship between the efficacy of EC and body weight, although the evidence suggests that it would be prudent to counsel patients at higher weights to use a copper IUD or UPA for EC. These methods are more effective than LNG for all women, but may in particular have additional benefit for women at higher body weights. There are obstacles to getting a prompt IUD insertion (including cost for uninsured women and service delivery issues such as clinic flow and two-visit protocols) and to getting UPA (such as the need for a prescription and the product frequently being out of stock). There is no health risk to taking LNG, so a heavier woman who does not have access to, or who does not want, an IUD or UPA for EC should still consider using LNG if she can afford it.

—James Trussell, PhD, and Kelly Cleland, MPA, MPH,

Office of Population Research, Princeton University




[1]  Creinin MD, Schlaff W, Archer DF, Wan L, Frezieres R, Thomas M, Rosenberg M, Higgins J. Progesterone receptor modulator for emergency contraception: a randomized controlled trial. Obstet Gynecol. 2006;108:1089-97.

[2] Fine P, Mathé H, Ginde S, Cullins V, Morfesis J, Gainer E. Ulipristal acetate taken 48-120 hours after intercourse for emergency contraception. Obstet Gynecol. 2010;115:257-63.

[3] 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.

[5] von Hertzen H, Piaggio G, Ding J, Chen J, Song S, Bártfai G, Ng E, Gemzell-Danielsson K, Oyunbileg A, Wu S, Cheng W, Lüdicke F, Pretnar-Darovec A, Kirkman R, Mittal S, Khomassuridze A, Apter D, Peregoudov A. Low dose mifepristone and two regimens of levonorgestrel for emergency contraception: a WHO multicentre randomised trial. Lancet. 2002;360:1803-10.

[6] Task Force on Postovulatory Methods of Fertility Regulation. Randomised controlled trial of levonorgestrel versus the Yuzpe regimen of combined oral contraceptives for emergency contraception. Lancet. 1998;352:428-33.

[7] Dada OA, Godfrey EM, Gilda Piaggio G, von Hertzen H. A randomized, double-blind, noninferiority study to compare two regimens of levonorgestrel for emergency contraception in Nigeria. Contraception. 2010;82:373-78.