The Health Service Executive has issued a warning about a dangerous drug which it says has caused the deaths of five people in Dublin and Cork since April.
They say the substance known as "designer" fentanyl or "synthetic" heroin can be up to 600 times more potent than morphine.
Two of the deaths were in Cork and three were in Dublin. They were as a result of overdose.
"Designer" fentanyl or "synthetic" heroin is sold in powder form possibly mixed with heroin, or caffeine and paracetamol to mimic heroin.
It can be snorted, swallowed or injected, or absorbed through the skin.
It is said to be dangerous taken by any route and even the smallest amount can result in overdose and death.
The HSE says that heroin users are most at risk to unwittingly taking this substance and are warning people not to take it.
The HSE Drugs and Alcohol Helpline is available Monday to Friday from 9.30am-5.30pm.
The confidential service has a freephone helpline, 1800-459-459, as well as an email support service helpline@hse.ie.
Information is also available on drugs.ie in relation to this substance.
