We enrolled healthy, reproductive-age women with obese and normal BMIs received 1.5 mg LNG orally and then in a subsequent menstrual cycle, the obese group also received 3 mg LNG. Total and free LNG PK parameters were obtained via serum samples through an indwelling catheter at 0, 0.5, 1, 1.5, 2, and 2.5 h. The primary outcome was the difference in total and free LNG concentration maximum (Cmax) between ECx1 and ECx2 in the obese group.