The hydrochloride salt of oxycodone, a methylether of oxymorphone and semisynthetic opioid agonist with analgesic and antitussive properties. Oxycodone binds to mu-receptors in the central nervous system (CNS), thereby mimicking the effects of endogenous opiates. In addition to analgesia and a depressive effect on the cough center in the medulla, this agent may cause euphoria, anxiolysis, miosis, sedation, physical dependence, constipation, and respiratory depression, depending on dosage and variations in individual metabolism. or A type of unstable molecule that contains oxygen and that easily reacts with other molecules in a cell. A build up of oxygen radicals in cells may cause damage to DNA, RNA, and proteins, and may cause cell death. An oxygen radical is a free radical. Also called reactive oxygen species.