Around 1,000 people in the North have been classified as "problem heroin users" with up to two-thirds not having received any treatment for their addiction, according to a new report.
The 12-month-study was commissioned by the Drug and Alcohol Unit of the Department of Health and carried out between November 2000 and October 2001.
It showed regional differences in the way heroin was used, with addicts in Ballymena, Co Antrim, likely to inject the drug, while those in Belfast tended to smoke heroin.
Users in Ballymena were also younger and predominantly male.
"Problem users" were defined as individuals who had experienced significant "social, psychological, physical or legal problems associated with the dependence, intoxication or regular consumption" of heroin.
The report also found that during the 12-month study period, only between 36 and 52 per cent of problem users received treatment.