The Eastern Regional Health Authority has said seven heroin users have died since the beginning of the month due to an "unidentified severe illness".
A total of 14 heroin users were admitted to hospital during this period.
Those who died had abscesses on their legs, arms and buttocks, according to gardai, which may have been due to injecting heroin into muscles instead of veins. But it is still not known how this could have led to the deaths.
The health authorities have said the deaths might have been linked to contaminated heroin.
On Wednesday, the Eastern Regional Health Authority said five drug users had died among 10 admissions to hospital, but last night it said these figures had increased with new information.
The authority said the hospital admissions and deaths appeared to be similar to a recent cluster of heroin deaths in Glasgow, where 11 people have died.
Mr Andrew Horne, of Turning Point, the largest drugs centre in Scotland, said the people who died in Glasgow were also admitted to hospital with abscesses. Eight of the 11 who died were women and Mr Horne said this may be due to the fact that long-term women drug users often lost the ability to inject into veins more quickly than men. He added that some of the women who died attended the same hostel in Glasgow and might have used the same heroin.
The Eastern Regional Health Authority said it was advising users who noticed an abscess, redness or swelling at the area of injecting to seek medical help immediately. It also advised heroin users to seek medical help if they developed any unusual or unexpected effects.
The authority has provided emergency methadone treatment vans in Blanchardstown and Ballymun, where no such treatment facilities exist. It said it was working with the Garda, the National Disease Surveillance Centre in Dublin and the Scottish authorities on a review of the situation. The authority added it was trying to identify common risk factors in the deaths of the heroin users.
Mr Tony Geoghegan, of the Merchants Quay Project, the voluntary drugs service which offers a needle exchange facility, said heroin users were aware of the situation but they had continued to inject heroin. "Scared doesn't come into it when people are looking for drugs," he said.
Mr Vincent Doherty, of the South Inner City Drugs Task Force, also said people were worried about the deaths but were continuing to take drugs.
"There is a temporary hype among users. Is it going to stop them buying heroin on O'Connell Street this evening? Is it going to stop them injecting? Not a chance."
Fine Gael TD Mr Gay Mitchell said there needed to be a more serious response to the problem. He said the Government needed a co-ordinated response from the Departments of Health, Justice, Tourism and Sport and Foreign Affairs.
"There needs to be a statement setting down what the Government are doing and what they are going to do to stop this from happening again," Mr Mitchell said.
He added that heroin users should be contacted in a more effective way to warn them of the dangers. "They don't read newspapers or listen to the radio. We need to go where they hang out and tell them. I don't feel the response is meeting the need."
Mr Tony Gregory TD said gardai on the north of Dublin city were aware of an increase in availability of heroin of varying strength and purity.