Prison Service figures show that 339 inmates were on restricted regimes last July. This fell 22% to 263 in September.
This includes a 20% fall in those being held on protection, who are kept away from the normal population for their own safety.
Of the 229 prisoners on protection, 213 were there at their own request. The other 16 were placed on protection for the safety of other inmates.
The drop follows a high-level review which was tasked by director-general Michael Donnellan to cut the number on restricted regimes and ensure, at a minimum, they had three hours out-of-cell time.
The figures show:
* A 56% drop in the numbers on 23-hour lock-up (the most restricted regime), dropping from 150 to 65;
* A 15% rise in those on 22-hour lock-up, increasing from 61 to 70;
* The 65 people on 23-hour lock-up include 46 there voluntarily and 19 for discipline reasons;
* Only one prison (Cloverhill) recorded a rise in 22- to 23-hour lock-ups (from 19 to 22);
* Wheatfield experienced the biggest drop (79 to 21);
* Numbers in St Patrick’s Institution for Young Offenders remained largely unchanged (17 to 16), but all 17 in July were on 23-hour lock-up and all 16 in September were on 22-hour lock-up.
“Recent efforts by the prison service to reduce the numbers of prisoners on protection are welcome,” said Fíona Ní Chinnéide of the Irish Penal Reform Trust. “However, we need more transparency around the lengths of time individual prisoners are being held on 22- or 23-hour lock-up.
“Being held in solitary confinement for more than 22 hours a day over longer periods is proven to be extremely harmful to prisoners’ mental health. Locking up anyone for 22 or 23 hours a day must only ever be used as a temporary measure and for the shortest time possible. It should not be a solution in itself to prisoner safety concerns.”