Helianorphin-19 is a high affinity, potent and selective κ-opioid receptor (KOR) agonist (Ki = 25 nM; EC50= 45 nM). Helianorphin-19 exhibits approximately 200-fold selectivity for KOR over μ and δ-opioid receptors.In vivoHelianorphin-19 shows potent peripheral analgesic efficacy in a mouse model of visceral pain without affecting motor coordination sedation.