Nociceptin (Orphanin FQ) is a 17 amino acid opioid-related neuropeptide that is a potent anti-analgesic and is widely distributed in the CNS. Endogenous ligand for the nociceptin receptor (NOP, pKi=8.6), but has no activity at the opioid receptors μ, δ, or κ (pKi<6). Plays a role in the regulation of reward and motivation pathways for substance abuse.