Mixed opioid receptor agonist/antagonist. Acts as a potent and full agonist at κ, a partial agonist at μ and δ opioid receptors (pEC50 values are 9.45, 8.74 and 8.61 in a cAMP assay, 9.70, 8.59 and 8.49 in a [35S]GTPγS binding assay respectively). Fails to exert agonist effects at NOP receptors and antagonizes agonist-induced NOP activation. Stimulates κ-, μ- and δ-mediated analgesia and blocks NOP-induced supraspinal nociception.