The hydrochloride salt of methadone, a synthetic opioid with analgesic activity. Similar to morphine and other morphine-like agents, methadone mimics the actions of endogenous peptides at CNS opioid receptors, primarily the mu-receptor, resulting in characteristic morphine-like effects including analgesia, euphoria, sedation, respiratory depression, miosis, bradycardia and physical dependence. Because of the prolonged half-life of merthadone compared to other morphine-like agents such as heroin, the onset of opiate withdrawal symptoms is slower, the duration of opiate withdrawal is prolonged, and opiate wihdrawal symptoms are less severe. or A drug used to treat moderate to severe pain that does not respond to other types of pain medicine. It is also used to help people who are addicted to opioid drugs such as heroin. Methadone hydrochloride binds to opioid receptors in the central nervous system. It is a type of analgesic agent and a type of opioid.