The number of drug seizures in Irish prisons increased by nearly 10% last year.
There was also a sharp rise in substances recovered in the State's detention centre for young offenders.
According to details released under the Freedom of Information Act, there were 1,138 drug seizures in jails across the country in 2018.
But this increased to 1,251 last year.
The highest numbers were in Dublin's prisons - with 490 in Wheatfield, 237 in Mountjoy and 186 in Cloverhill.
Dr Greg Kelly, a former GP in Castlerea Prison in Co Roscommon, said he was surprised by the findings.
He said: "It actually amazes me that they're not picked up and detected when coming into the prison.
"If you can't control the flow of drugs into a prison, it is no wonder that it's so difficult to control it in the whole country and to control it coming into the country.
There was also a big jump in drug seizures in Oberstown Children's Detention Campus last year with 32, compared to seven the previous year.
As of December 31st, there were 31 boys and two girls in the detention centre.
A spokesperson for Oberstown said: "There is always a challenge in keeping drugs out of any secure setting.
"We have a process in place which we follow when young people enter the campus and for those visiting to ensure drugs are not brought in and we have invested in new mechanisms to help us keep the campus drug free."