Detectives fear that further deaths from fentanyl will be confirmed in the coming weeks, adding to the five people who died between April and July — the first such deaths in the country.

Officers are particularly concerned at two recent developments:

- Three men were taken into intensive care a fortnight ago after they snorted what they thought was cocaine at a christening party in south-west Dublin and narrowly avoided death;

- Gardaí seized 1kg of drugs in north Dublin over a week ago which contained fentanyl. It was the first large seizure of the drug.

Sources said the deaths, the seizure, and the overdoses were all “unconnected” — pointing to separate routes of supply.

This includes the involvement of drug trafficking gangs which are capable of importing large amounts.

“We have had five recorded deaths so far, we have our first bulk seizure of the product, and we have three overdoses, which also shows it’s threatening not just heroin users but cocaine users,” said a source.

Two weeks ago, three men at a christening reception at a community centre in Tallaght collapsed after snorting a line of what they thought was cocaine.

It is understood they suffered respiratory failure and ended up in Tallaght Hospital intensive care unit. Sources said they were lucky to survive. It was discovered that the cocaine contained fentanyl.

Fentanyl is a synthetic opiate and is toxic at incredibly small doses, around 2mg. A source said that what would fit on the top of a finger would be enough to kill a user.

“We have feared for years that fentanyl would come here,” said the source. “Now it looks like it’s here to stay.”

The first death occurred in Cork on April 27, after a young man consumed a type of fentanyl called fluorofentanyl which was bought off the dark web (underground internet).

It was not until the deaths of three homeless heroin users in Dublin over four days, between May 25 to 28, did gardaí have a situation where the drug, this time a variation called ocfentanyl, was supplied on the street.

Then on July 27, there was another death in Cork, from fluorofentanyl — this time purchased on the street.

The 1kg of product seized contained fentanyl mixed with paracetamol and caffeine (called ‘bash’). The EU drugs agency said fentanyl was linked to 650 deaths in Estonia between 2005 and 2012, around 160 deaths in Germany between 2008 and 2011 and some 59 deaths in Sweden in 2010 and 2011.

HSE Helpline 1800 459 459; helpline@hse.ie