Nalfurafine is a naltrexone derivative and a potent, selective agonist for human kappa-opioid receptors. It is devoid of action on mu or delta opioid receptors. It inhibited intradermal histamine- or substance P-induced scratching in mice, rats and monkeys, implying potential for improvement over a wide variety of itch. Its antipruritic activity was antagonized by nor-BNI, a kappa-opioid receptor antagonist. Nalfurafine produced slight physical dependency in rats but no reinforcing effects in primates. It was approved by the Japanese health authority in January 2009 (Nakao, K. Acta Derm Venereal 2009, 89: 706, Abst OP64).