Although it is known that the use of oral contraceptives (OC's) can induce glucuronide conjugating enzymes, currently no data exists as to the potential that the elimination of the glucuronidated drug lamotrigine (LTG) is increased by OC's. We present seven cases in whom the plasma levels of LTG were significantly decreased by OC's (mean 49%, range 41-64%). The interaction was of clinical relevance in most of the patients who either experienced increased seizure frequency/recurrence of seizures after OC's had been added, or adverse effects following withdrawal of OC's.