Dynorphin A and nociceptin/orphanin FQ (N/OFQ) are both 17 aminoacid opioid peptides, sharing high sequence similarity but belonging to distinct systems. Electrophysiological, biochemical, pharmacological, and clinical data support the hypothesis that dynorphin plays a role as an endogenous anticonvulsant in complex partial seizures and in some cases of tonic-clonic seizures, but most likely not in generalized absence. This pattern of effects coincides with the antiseizure spectrum of selective κ agonists. Studies on the effects of agonists in epileptic patients have not been performed yet. In contrast with dynorphin, the possible role of N/OFQ in epilepsy is still very unclear. Available data suggest that its contributions may be complex, with different effects in different seizure and epilepsy types. Therefore, a careful examination of the precise indications of drugs affecting the N/OFQ system in the different epilepsy types is needed
