The Irish Penal Reform Trust (IPRT) has said that overcrowding is contributing to some of the issues with drugs in Irish prisons.
Its executive director Saoirse Brady was commenting after 11 prisoners at the Midlands Prison were hospitalised for suspected overdoses.
Speaking on RTÉ's Morning Ireland, Brady said that prison numbers stood at 5,017 yesterday (13 August) across all prisons – a figure that represents 112% of capacity.
She added that many people in the prison system had an existing addiction, and did not always get the support that they needed while in prison.
"There is a health-led approach in the community to substance misuse, and the emphasis should be on that within the prison estate as well, taking into account the security considerations that are there. Drug use in prison does happen and a zero-tolerance approach doesn't always work," Brady said.
Last month, the Irish Prison Service issued an urgent drug alert to all prisons after analysis conducted by the HSE National Drug Treatment Centre Laboratory that confirmed the presence of a nitazene-type substance linked to overdoses in Irish prisons.