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In Europe, labeling of levonorgestrel emergency contraceptive (EC) pills states that women weighing >80 kg (176 lbs) may be more likely to experience EC failure. To evaluate obesity's effects on the pharmacokinetics of 1.5-mg levonorgestrel tablets, investigators enrolled five obese women (body mass index ≥30 kg/m2) and five normal-weight women with regular menstrual cycles.
After a single EC pill, the obese women had significantly lower peak serum levels of levonorgestrel than their normal-weight counterparts. After doubling the EC dose, peak levels of levonorgestrel among obese women were similar to those of normal-weight women who took a single EC dose.