11 inmates were hospitalised as a result of the drug last week.
The HSE says the drug identified in the Portlaoise Prison overdoses is unlikely to be circulating in festivals or nightlife settings.
A new synthetic Benzodiazepine has been deemed responsible, after 11 inmates were hospitalised last week.
National Clinical Lead of Addiction Services at the HSE, Professor Eamon Keenan, says it's the first time the drug has been identified in Ireland, and it's a sedative.
As a result, he thinks it's unlikely to be circulating around festivals or in other nightlife settings, as they tend to see stimulants.
However, Professor Keenan says the situation at Portlaoise Prison is an example of how volatile the drug market is, and new substances are appearing on the market and causing harm quickly.
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