Orphanin FQ(1-11) TFA, a orphanin FQ or nociceptin (OFQ/N) fragment, is a potent NOP receptor (ORL-1; OP4) agonist, with a K i of 55 nM. Orphanin FQ(1-11) TFA has no affinity for μ, δ, κ1 and κ3 receptors (K i >1000 nM). Orphanin FQ(1-11) TFA is analgesic in CD-1 mice.