A substance made from morphine. Diamorphine hydrochloride is very addictive, and it is illegal to use or sell it in the United States. It may be used outside the United States to treat severe pain. Diamorphine hydrochloride binds to opioid receptors in the central nervous system. It is a type of analgesic agent and a type of opiate. Also called diacetylmorphine hydrochloride and heroin.