Methadone, sold under the brand names Dolophine and Methadose among others, is a synthetic opioid agonist used for chronic pain and also for opioid dependence. It is used to treat chronic pain, and it is also used to treat addiction to heroin or other opioids. Prescribed for daily use, the medicine relieves cravings and removes withdrawal symptoms. Detoxification using methadone can be accomplished in less than a month, or it may be done gradually over as long as six months. While a single dose has a rapid effect, maximum effect can take up to five days of use. The pain-relieving effects last about six hours after a single dose. After long-term use, in people with normal liver function, effects last 8 to 36 hours. Methadone is usually taken by mouth and rarely by injection into a muscle or vein.Side effects are similar to those of other opioids. These frequently include dizziness, sleepiness, vomiting, and sweating. Serious risks include opioid abuse and  respiratory depression. Abnormal heart rhythms may also occur due to a prolonged QT interval. The number of deaths in the United States involving methadone poisoning declined from 4,418 in 2011 to 3,300 in 2015. Risks are greater with higher doses. Methadone is made by chemical synthesis and acts on opioid receptors.Methadone was developed in Germany around 1937 to 1939 by Gustav Ehrhart and Max Bockmühl. It was approved for use as an analgesic in the United States in 1947, and has been used in the treatment of addiction since the 1960s.
The salts of methadone in use are the hydrobromide (free base conversion ratio 0.793), hydrochloride (0.894), and HCl monohydrate (0.850). Methadone is also regulated internationally as a Schedule I controlled substance under the United Nations Single Convention on Narcotic Drugs of 1961. Methadone clinics
In the United States, prescription of methadone requires intensive monitoring and must be obtained in-person from an opioid treatment program—colloquially known as a methadone clinic—when prescribed for opioid use disorder (OUD). According to federal laws, methadone cannot be prescribed by a doctor and obtained from a pharmacy in order to treat addiction. Because of its long half-life, methadone is almost invariably prescribed to be taken in a single daily dose. At nearly all methadone clinics in the US, patients must visit a clinic to receive and take their dose under the supervision of a nurse. Both patients who are new to methadone treatment and high-risk patients—such as those who are using drugs and alcohol, including cannabis—must visit the clinic daily. However, some clinics close on national holidays and provide doses to patients to take home. Take-home or take-away methadone
After 90 days to six months (depending on the clinic), if patients have met the clinics criteria, they are typically eligible for take-home doses of methadone. Therefore, they may be allowed to take anywhere from one to six days to visit the clinic once or twice weekly instead of every day.