Generally speaking, methadone is prescribed for people with a diagnosis of opiate dependence. This goes above and beyond just abusing opiates: you are dependent on opiates. It's a long-term treatment. Generally speaking, it's not something that you go on and then go off. It's a substitute for an opiate. The effect does not provide the euphoric high that you would get using an opiate. It stops the craving and it also stops the withdrawal. It allows a person to stabilize so that they no longer go through the cycle of craving a drug and withdrawing from the drug.
There are instances, though, where people either voluntarily or involuntarily stop the program. In those instances, working very closely with the physicians, the drug is tapered very, very slowly to reduce the symptoms of withdrawal, but people still experience withdrawal.