Methadone hydrochloride is a typical agonist at the mu-opioid receptor that controls opioid withdrawal symptoms. Compared with morphine, it has a stronger analgesic effect and can produce respiratory depression, pupil constriction, sedation and other effects. Its analgesic effect is longer, not easy to produce drug resistance, not easy to become addicted; oral absorption is better, 30 minutes after taking the drug to take effect, 4 hours later the blood concentration will reach the peak, the effect time in 24-36 hours. It is mainly used for the analgesic treatment of severe pain caused by trauma, postoperative pain, cancer, etc. It is also applied to the detoxification treatment of opioid dependence, such as commonly used in drug rehabilitation centers for the follow-up treatment of drug addicted patients.