There are 48 inmates of Cork Prison on a waiting list for methadone treatment for opioid addiction, while a further 47 are being treated for it.
That is according to the most recent figures available from the Department of Justice, for March 1, when there were 267 inmates in the prison.
Those on the waiting list and those receiving the treatment combine to make up 35% of the prison population.
There are currently 522 prisoners in receipt of methadone across the entire prison system.
Criminologist and presenter of The Two Norries podcast James Leonard, who is a recovering heroin addict, said the provision of methadone to heroin addicts in prison is as important as providing insulin to diabetics.
He said he was not on methadone when he was imprisoned and, as a result, he suffered major withdrawal symptoms from heroin when in prison.
He added: “It is much more humane now.”