Stormont ministers have launched a review of how vulnerable prisoners are monitored following a number of recent suicides and self-harm incidents.
Justice Minister Claire Sugden and Health Minister Michelle O'Neill are jointly undertaking the probe.
Five people have died in custody in the last 12 months - four of whom were suspected suicides.
Prison authorities were also heavily criticised in a recent damning report by the Prisoner Ombudsman after an inmate inflicted extreme self-harm on himself in Maghaberry high security jail in June 2014.
Ms Sugden announced the review in a statement to the Assembly.
She also revealed that this month, the prison population totalled 1,533. Of these, 417 were recorded as having a mental health illness and a further 740 prisoners recorded as having an addiction - just over 75% of the prison population.
"I know members appreciate the scale of the challenge in respect of mental health in prisons and the need for joined up partnership working to address that challenge," she said.
Ms Sugden said full investigations of the suicide incidents inside Maghaberry were ongoing and officials were also endeavouring to develop a "community response plan" to prevent further deaths. She said the Prison Service's suicide and self-harm policy was also being re-examined.