Some epilepsy patients are described as GB when they have worsened seizures or side effects related to switching between brand name and generic, or between generic antiepileptic drug (AED) products. In concert with Aim 1 (protocol BEEP2a), this study will uncover possible reasons for patient problems with the drug switching. Factors that will be studied in GB epilepsy patients include physiologic, psychological, and genetic factors, including in this protocol whether brand and generic AEDs are pharmacokinetically similar in GB individuals.