UFP101 is a synthetic peptide that functions as an antagonist of the nociceptin receptor, demonstrating high affinity with a Ki of 0.06 nM in CHO cells expressing the human receptor. It exhibits selectivity for the nociceptin receptor over the κ-opioid receptor, with a Ki of 204 nM in CHO cells expressing the rat receptor. The compound effectively inhibits GTPγS release from the nociceptin receptor in CHO cell membranes, with an EC50 of 1.86 nM. When administered intracerebroventricularly at a dose of 10 nmol/animal, UFP101 prolongs the latency to tail withdrawal in the tail-flick test in mice, indicating its potential as an analgesic. Additionally, at doses of 0.003, 0.03, and 0.3 mg/kg, UFP101 enhances survival in a sepsis mouse model induced by cecal ligation and puncture, suggesting potential therapeutic applications in sepsis management.