OPRM1 and Respiratory insufficiency due to muscle weakness: This dual action provides analgesia while minimizing adverse effects associated with MOR agonists, including opioid-induced pruritus (OIP), respiratory depression, and nausea.1, 2, 3 First approved as an analgesic in 1979, nalbuphine is now generic and Food and Drug Administration–approved for the management of moderate to severe pain.