How is methadone used to treat drug abuse?

Methadone is giving for two reason one is for chronic pain and the other is to detox a person who is addicted to opiates. methadone is an opiod which is addictive its self but it stays in your body longer and you dont get the high feeling from whatever opiates you were using and then when the dr feels its time they will slowly bring you off the methadone