There are more people seeking treatment for heroin addiction in the north inner city than anywhere else in the country.
And nearly half of addicts have been on methadone for over ten years.
New figures from the HSE show that more than 3,300 addicts have been taking methadoe for over ten years, while 178 people have been on the programme for over two decades.
Tallaght has roughly the same number of addicts seeking treatment as in the south inner city.
It's believed that running the methadone treatment plan for the last 20 years could have cost up to €200 million.
Currently, it costs almost €20 million every year.
Questions are being raised about the success of the plan, which was designed to replace heroin with a less dangerous medication- with the aim of weaning addicts off drugs.
It costs €1,700 to maintain an addict on the programme for a year.
