Ten prisoners are being treated for suspected overdoses at Portlaoise Prison.
The Irish Prison Service (IPS) said it is “working closely” with the HSE in response to a number of overdose presentations in custody.
The prison service has secured extra naloxone kits and said “extra vigilance” is being taken.
In a statement, the IPS said preventing drugs and other contraband from entering prisons is a high priority.
It said: “The Irish Prison Service has committed to continuing to invest in new technologies and measures to support our efforts to keep contraband out of prisons.
“Prison staff have increased the use of random and intelligence-led cell searches on a daily basis. Our Canine Unit carry out searches around the prisons, including a greater focus on searching deliveries into prisons.
“The Irish Prison Service continues to engage with An Garda Siochana with regard to preventing contraband entering our prison and this happens at both local and national level.”