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At the same time, just one in eight male prisoners were on methadone.
Over half of female prisoners are on methadone, which is normally used to treat an addiction to heroin.
There were 104 on the drug at the end of last year - out of 189 women in jail at the time.
According to freedom of information figures, only one in eight male prisoners were on methadone at the time.
Former governor of Mountjoy and Portlaoise Prisons, John Lonergan, is not surprised by the figures relating to women: