Almost a quarter of Ireland's heroin addicts are now based outside Dublin, according to a recent study.

The survey by Merchant's Quay Ireland, which compiles statistics from the Gardaí, treatment clinics and other agencies, pinpoints those using the class A drug across the country.

The spread of heroin abuse means that no county has escaped the epidemic.

There are now 21,000 addicts in the state, with 16,000 in the greater Dublin area.