A prison officer is among three people arrested as part of an investigation into trafficking prohibited items into Maghaberry.
A quantity of suspected Class A and B controlled drugs and drugs paraphernalia was seized during searches carried out at HMP Maghaberry and other properties on Friday.
The 23-year-old was detained on Friday morning at the prison on suspicion of conveyancing prohibited articles into a prison, misconduct in public office, possession of criminal property and being concerned in the supply of Class A and B drugs, as well as prescription medication, following a joint operation with the Prison Service.
He was taken to Musgrave Police Station for questioning.
Two women, aged 26 and 55, were also arrested following searches of properties in Lisburn and Dungannon as part of the investigation.
The 26-year-old was bailed on Saturday. The prison officer and 55-year-old woman remain in police custody.
Detective Chief Inspector Brian Foster, from the PSNI’s Criminal Investigation Branch, said: “This operation is a good example of how collaborative working can disrupt crime and also demonstrates our commitment to Keeping People Safe by removing harmful drugs from society.
“We will continue to work closely with the Prison Service to clamp down on the trafficking of illicit drugs into prisons.”
Welcoming the outcome of the joint operation, Head of the Northern Ireland Prison Service, Ronnie Armour, said: “Removing dangerous drugs from Maghaberry will help to keep staff and prisoners safe. I would commend everyone involved in this operation.”