Methadone, the substance used in the rehabilitation of heroin addicts, was found in the bodies of 45 drug-users who died in Dublin in 1999.
The chief executive of the Eastern Regional Health Authority (ERHA), Mr Donal O'Shea, said it was not possible to tell whether methadone, prescribed or otherwise, was the cause of death in any of these cases.
Mr O'Shea said the Dublin Coroner's inquest records for 1999 showed that methadone was present in 45 cases, but only in one case was it the only substance found. In half the cases three or more substances were identified.
"Apart from opiates the most prevalent substances detected were benzodiazepines and alcohol. Of the 45 cases where methadone was found it was being prescribed as per guidelines in 15 cases," he added.
Dublin city councillor Ms Catherine Byrne, a member of the health authority, had asked for statistics on the number of deaths resulting from methadone treatment. She also asked if methadone was a suitable treatment for addicts in recovery.
Mr O'Shea said some addicts opted to stay on methadone while undergoing rehabilitation programmes while others opted for detoxification.
"The treatment of choice is a matter between the drug-taker, their doctor and other members of the care team. Two independent evaluations of the drug treatment services in the Eastern region have endorsed the approach being taken," he said.
There are about 5,000 drug abusers on methadone treatment programmes in the region.