Two women are said to be in a life-threatening condition in hospital in Co Louth after consuming cannabis which may have been contaminated or mixed with another substance.
Both are in their twenties and are in the intensive care unit of Our Lady of Lourdes Hospital in Drogheda.
Gardaí in Drogheda have recovered a quantity of cannabis and it is being tested to identify exactly what it contains.
There are concerns that it may be contaminated or mixed with a synthetic substance as the effects suffered by the women are not usually caused by cannabis on its own.
Garda Superintendent Gerry Smith of Drogheda garda station said he is "concerned that other people who use cannabis may suffer the same effects".