Oxymorphone hydrochloride. Molecular model of the drug oxymorphone hydrochloride (C17.H19.N.O4?H.Cl). This semi-synthetic opioid analgesic is sold under the brand name Opana ER. It is indicated for the relief of moderate to severe pain and also as a preoperative medication to alleviate apprehension, maintain anaesthesia and as an obstetric analgesic. Atoms are represented as spheres and are colour-coded: carbon (grey), hydrogen (white), nitrogen (blue), oxygen (red) and chlorine (green).