Methadone is a long-acting µ-opioid receptor agonist with potent central analgesic, sedative and antitussive actions. Methadone inhibits ascending pain pathways, alters the perception of and response to pain, and produces generalized CNS depression. It is used as an analgesic for the relief of moderate to severe pain and is used in the detoxification treatment of opioid dependence. When used to treat addiction, methadone suppresses withdrawal symptoms for 24 to 36 hours. When administered orally, methadone is rapidly absorbed from the gastrointestinal tract and can be detected in the blood within 30 minutes. The half-life of (R, S)-methadone is 15-60 hours, and 10-40 hours for (R)-methadone.
