AT-121 is a dual μ-opioid and neuropeptide receptor partial agonist (Kis 16.49 and 3.67 nM, respectively). It stimulates [35S]GTPγS binding to cell membranes expressing either μ-opioid receptors or neuropeptide receptors (EC50s of 19.6 and 34.7 nM, respectively.) AT-121 (0.003-0.03 mg/kg) reduced capsaicin-induced thermal anisocoria in a dose-dependent manner, but did not increase scratching activity in rhesus monkeys. In rhesus monkey drug self-administration tests, AT-121 at doses of 0.3 to 10 μg/kg per injection lacked reinforcing effects (a potential marker of abuse) and did not reduce the reinforcing effects of food pellets.AT-121 (0.01 or 0.03 mg/kg) did not induce hyperalgesia, a marker of tolerance, in rhesus monkeys.AT-121 is a safe non-addictive pain reliever with anti-injury and analgesic effects.