The HSE has defended having thousands of drug addicts on methadone for more than a decade, claiming the medication stops people relapsing onto heroin with the unintended consequences of drug-driven crime, overdose death rates and the spread of hepatitis and HIV.
Nearly 180 people have been on methadone for 20 years or more, and the cost of treating around 10,000 people affected by the scourge of addiction now stands at nearly €20m a year.
But the HSE claims there is evidence that methadone maintenance is cost-effective.
"The failure to provide Opioid Substitution Therapy (OST) in the early 1990s fuelled the phenomenal epidemic of heroin dependence that was rampant in the most deprived communities of Dublin in the mid-1990s," said a HSE spokesperson.
The HSE also pointed to UK research which suggested that health agencies that limit methadone therapy to drug users could face legal challenges.
In the UK in 2006 there was a legal challenge from a group of 200 ex-prisoners who claimed they had been given inadequate treatment for opiate withdrawal while in jail.
The Home Office settled out of court and had to pay damages to the prisoners.
There was criticism of the numbers of drug users on the HSE methadone programme in Ireland this week when the Herald revealed the length of time that many addicts have been in treatment.
The HSE said a report from the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) showed that no country of the 20 surveyed, including Ireland, imposes a limit on the amount of time a person can be on methadone.
However, Fianna Fail health spokesman Billy Kelleher called for an independent assessment of the methadone programme to see if it is right one for all of those on it.
"The methadone itself is relatively cheap and there is a risk that it just gets dispensed to keep addicts quiet and reduce the risk of them committing crime when actually many who are on it might benefit from a different treatment," he said.
His views were echoed by the Merchants Quay project which offers drug treatment.
"Methadone is intended to take people out of the vicious cycle of criminality, but it can be argued that the current system does not provide a follow-through with a personal treatment plan to help people move forward," said chief executive Tony Geoghegan.