Effect of hormonal contraceptives on lamotrigine pharmacokinetics In a study of 16 female volunteers, dosing with 30 µg ethinyloestradiol/ 150 µg levonorgestrel in a combined oral contraceptive pill caused an approximately two-fold increase in lamotrigine oral clearance, resulting in an average 52% and 39% reduction in lamotrigine AUC and Cmax, respectively.