A seclusion room at the scandal-hit Muckamore Abbey Hospital was used 745 times in 2015, new figures have revealed.
The BBC reports that 21 patients were placed in the controversial room at the County Antrim hospital at least once.
The Belfast Health Trust told the BBC the room was used to treat patients with aggressive behaviour. It was also used for patients being angry, anxious, challenging, threatening or requesting time out.
The news comes following a damning review surrounding the protection of vulnerable adult patients at the hospital, published last month, which found that many lives were compromised.
The report listed a series of catastrophic care failings and said there was a "culture of tolerating harm" at the hospital.
Figures show the seclusion room was used 745 times in 2015, compared to 159 occasions last year.
The BBC found that in spite of 80 men and women being treated at the hospital, on average it was the same 21 patients who were subjected to the room on one or more occasion during 2015.
The Belfast Health Trust's policy on seclusion states that it is an emergency procedure and that it should only be used as a last resort.
Since 2018, the trust changed its policy meaning that only a consultant can authorise the use of the seclusion room. Prior to this change, a more junior medic could have granted permission.
A Belfast Trust spokesman said: "Seclusion may be used as an emergency management procedure to contain severely challenging behaviour which is likely to cause harm to the patient themselves or to others.
"Where indicated and in line with the policy practised in certain contexts of Learning Disability Inpatient Services.
"Staff have clear guidance on the use of seclusion. A patient is assessed by a nurse in charge and monitored at all times.
"It should only be used for shortest time possible and kept under constant review.
"The Trust’s seclusion policy in relation to Muckamore Abbey Hospital is currently under review by a multi-disciplinary team which will fully engage with patients, carers and staff.
"The use of seclusion to de-escalate a situation where a patient may harm themselves or others has declined in recent years. Whilst the practice of using seclusion is changing, the decision to do so rests with the clinical team in line with guidelines and best practice."