Nalbuphine is an opioid pain medication. An opioid is sometimes called a narcotic. Nalbuphine is used to treat moderate to severe pain. It is also used for treating pain just after surgery or childbirth. Nalbuphine may also be used for purposes not listed in this medication guide. Nalbuphine is injected under the skin, into a muscle, or into a vein through an IV. A healthcare provider will give you this