One chaplin described the habit as impossible to avoid.
The amount of drugs coming into jails is 'extremely concerning', according to some prison chaplains.
Their 2019 annual reports have been released under the Freedom of Information Act.
Mountjoy Prison's chaplaincy service says it's almost impossible to avoid the temptation of drugs within the jail.
Chaplains in Wheatfield Prison in Dublin say prisoners arriving into jail clean can leave addicted - and some inmates refuse to go to the prison yard for fresh air, due to drug activity.
Former Portlaoise Prison governor John Lonergan says drugs have been a problem in jails for decades:
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