There are several commonly proposed hypotheses of drug-resistant epilepsy (32), which have been summarized as the “drug transporter hypothesis,” “altered target hypothesis,” and “missing target hypothesis.” The drug transporter hypothesis is based on the observation of increased expression of efflux drug transporters (P-glycoprotein, BCRP, MRPs, and other ABC transporters) at the apical surface of cerebral capillary endothelial cells at the epileptogenic lesion. The gene discussed is ABCG2; the disease is epilepsy.