Side effects of antiepileptic drugs may affect quality of life even more than seizures. In a study of 1,694 adults with epilepsy, patient-reported cognitive side effects were most common with topiramate, zonisamide, phenytoin, and oxcarbazepine. The study, published in Epilepsy & Behavior, found an intolerability rate of about 13% overall. Via Neurology Advisor. Posted January 16, 2015.