Nalbuphine (HCl) is a synthetic opiate agonist/antagonist that is chemically related to both naloxone, a narcotic antagonist, and oxymorphone, a potent narcotic analgesic. Used to treat moderate to severe pain associated with acute and chronic medical disorders such as cancer, renal or biliary colic, migraine or vascular headaches, and surgical pain. Another clinical use is obstetrical analgesia during labor and delivery. Some evidence suggests that nalbuphine's respiratory depressant effects do not increase proportionately with increasing doses, thus making this drug safer in patients at risk from respiratory depression. It was approved by the FDA in 1979. Nalbuphin exerts its effects by binding to specific opiate receptors present in the central nervous system, functions as an antagonist at the µ-receptor, however it has agonist action at ?-receptor, Nalbuphine is also an agonist at the d-receptor, but Nalbuphine (HCl) is nalbuphine's action at the ?-receptor that provides analgesia. Actions at the ?-receptors are believed to produce alterations in the perception of pain as well as the emotional response to pain, possibly by altering the release of neurotransmitters from afferent nerves sensitive to painful stimuli.