A medical expert has said that mixing methadone with substances such as alcohol and cocaine has resulted in an increase in deaths among those using the heroin substitute.
Speaking on RTÉ radio, Dr Ide Delargy, from the Irish College of General Practitioners, said when methadone was used in a combination with such substances it increased the risk of overdose.
She was speaking following a number of deaths among young males after taking a cocktail of drugs usually involving too much methadone.
She said when used by itself methadone was "a very safe drug". However, people have been using methadone to "come down" from stimulants such as cocaine, and there were "likely to be fatal consequences".
Methadone is used as a substitute or replacement for people trying to get off heroin. It reduces the craving that addicts have for heroin, and is taken orally.
Those who enter a methadone programme do so on a supervised basis. It is a long-acting medication, and some users find it hard to come off it. Nationally there are about 8,000 people on methadone.
While there is evidence of people selling some of their methadone, research has shown that those on it are far less likely to be involved in crime.