A synthetic opioid with analgesic activity. Methadone mimics the actions of endogenous peptides at CNS opioid receptors, primarily on the mu-receptor and has actions similar to those of morphine and morphine-like agents. The characteristic morphine-like effects include analgesia, euphoria, sedation, respiratory depression, miosis, bradycardia and physical dependence. However, the detoxification symptoms between morphine-like agents and methadone differ in that the onset of methadone''s withdrawal symptoms is slower, the course is more prolonged and the symptoms are less severe. [from NCI]