Nalbuphine hydrochloride (Nubain) is classified as a synthetic opioid agonist-antagonist. Chemically, it is related to the opioid antagonist, naloxone and the potent opioid agonist oxymorphone. The chemical name for nalbuphine is 17-(cyclobutylmethyl)-4,5α-epoxymorphinan-3,6α, 14- triol hydrochloride.