NUBAIN (nalbuphine hydrochloride) is a synthetic agonist-antagonist in the phenanthrene series. It is chemically related to both the widely used opioid and the potent opioid pain reliever, oxymorphone. Chemically, nalbuphine hydrochloride is 17-(cyclobutylmethyl)-4,5-epoxymorphinan-3,6,14-triol hydrochloride.