High Quality Content by WIKIPEDIA articles! Oxymorphone (Opana, Numorphan, Numorphone) or 14-Hydroxydihydromorphinone is a powerful semi-synthetic opioid analgesic first developed in Germany circa 1914, patented in the USA by Endo Pharmaceuticals in 1955 and introduced to the United States market in January 1959 and other countries around the same time. It (along with hydromorphone) was designed to have less incidence of side effects than morphine and heroin. It was a success as it differs from morphine and heroin in its effects in that it generates less euphoria, sedation, itching and other histamine effects at equianalgesic doses. This also means a lower dependence liability.