Ten prisoners have been taken to hospital after suspected overdoses at Portlaoise Prison.
The prisoners were brought to the Midlands Regional Hospital, County Laois, on Tuesday afternoon.
RTÉ News understands the prisoners are all in a serious condition.
The Irish Prison Service (IPS) said it was working closely with the health service and it had secured extra naloxone kits. Naxolone is a prescription medication used to temporarily reverse the effects of opioid drugs.
The IPS issued an urgent drug alert to all prisons in July following a detection of the drug nitazene, which resulted in a fatal overdose.
On Tuesday, the IPS said extra vigilance was being taken across the prison estate.
As well as securing extra naloxone kits, the IPS said it had commenced an “information campaign for prisoners around the dangers of consuming contraband”.
The prison service has also “increased the use of random and intelligence led cell searches on a daily basis”.