11 inmates in total were affected by the incident.
All prisoners affected by the overdoses at Portlaoise Prison have been discharged from hospital.
11 inmates in total were taken to Regional Hospital Portlaoise for treatment after the incident on Tuesday.
The last of those had been receiving treatment in ICU - they were discharged yesterday.
A quantity of white powder, believed to be a synthetic opioid, was discovered in the prison's C Wing earlier this week.
An investigation is now underway into what exactly the drug was and how it got into the jail.
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