Methadone is a medication used to treat opioid use disorder (OUD) . It is a long-acting full opioid agonist and a schedule II controlled medication. Methadone has been used for decades to treat people who are addicted to heroin and narcotic pain medicines. When taken as prescribed, it is safe and effective, allowing people to recover from their addiction and to reclaim active and meaningful lives. Methadone works by changing how the brain and nervous system respond to pain. It lessens the painful symptoms of opiate withdrawal and blocks the euphoric effects of opiate drugs such as heroin, morphine, and codeine, as well as semi-synthetic opioids like oxycodone and hydrocodone. Methadone is offered in pill, liquid, and wafer forms and is taken once a day. Pain relief from a dose of methadone lasts about four to eight hours. Methadone is used to relieve severe pain in people who are expected to need pain medication around the clock for a long time and who cannot be treated with other medications. Methadone is taken as a replacement for heroin and other opioids as part of a treatment known as pharmacotherapy, which has been around for more than 40 years.