When is methadone addictive?

[bethoven]

Methadone is a good drug when used according to the prescriptions of the doctor. I wonder why and when does it become addictive to the person using it?
Is anyone allowed to buy this methadone in the drugstore without the medication of the doctor?

[danieltooop]

Methadone is very addictive. Because it works on the central nervous system, an individual’s brain can become too well adjusted to relieving pain by means of methadone versus using natural painkillers called endorphins. Everyone has naturally produced endorphins that will help to cut pain. When these become deadened or degenerated due to narcotic use, however, an individual will seek outside pain relief through the continued use of the narcotic.