Commonly used names include meth, linctus.

The law:
Methadone is a prescription-only drug used to treat people who have become dependent on opiates such as heroin.
When possessed without a prescription, or supplied illegally, methadone is treated as a Class A drug.

How it is taken:
Methadone is normally supplied as a colourless or green liquid, but is also available in tablet and ampoule form.

Effects:
When taken in large amounts, the effects of methadone are similar to those of heroin.
Methadone – although itself addictive – is less addictive than heroin, which is why it is used under medical supervision to treat heroin addiction. However, the use of methadone carries its own considerable risks (see below).

Risks:
Methadone is addictive.
Medically supervised use of methadone involves careful monitoring and regulation of doses.
Use without medical supervision is very dangerous, and carries the risk of fatal overdose, which may not be recognised because methadone acts more slowly than heroin when taken orally.