37% of Mountjoy inmates on methadone

Thirty-seven percent of inmates in the Mountjoy Prison complex are on methadone, which is normally used to treat an addiction to heroin.

Twenty percent of those in the men's jail are on the substance, and 46% in the women's section.

That compares to an average of 17% in all Irish prisons, according to details released under the Freedom of Information Act.

Dr Greg Kelly said methadone should only be given to prisoners for a very short period.

He said: "As regards giving it to them long term, it makes no sense to me at all because they may be in prison for months and years and be still taking an amount of methadone every day which is an addictive drug.

"I fail to understand the reasoning behind it."