One prisoner remains in ICU this morning following the overdoses at Portlaoise Prison.
It's understood he's in a serious condition but is responding to treatment.
11 inmates in total had to be taken to hospital after a suspected synthetic drug was taken on Tuesday.
An investigation is now underway into what exactly the drug was and how it got into the jail.
Former Garda Commissioner Michael O'Sullivan says it's impossible to stop drugs getting into prisons:
"The Prison Service are doing their best, and they're working closely with the Gardai. But you know, what are you talking about? You could be talking about a dessert spoon full of drugs, very easily concealed by a visitor, or, as they sometimes do, throw drugs over the walls and there are nets there to try and catch them, etc".
