Matthew John Millard spent the past three weeks handcuffed to a hospital bed and under constant guard after taking the pills and falling unconscious.

He was revived after another detainee sounded the alarm but the 29-year-old suffered serious brain damage after his oxygen supply was cut for several minutes.

The injured man, who had a history of overdosing on drugs, was not expected to fully recover from the brain damage.

The news came after revelations paedophiles at the jail had allegedly formed a pornography ring, obtaining and distributing electronic images of child abuse.

The ACT opposition and a former commander of the jail said on Friday there were serious question marks over the supervision regime and the political oversight of the jail

But Corrections Minister Shane Rattenbury said he had been kept briefed on Millard's overdose.

"There's a range of things that happen in the prison and I'm generally kept up to speed with them," Mr Rattenbury said. "Due to privacy issues I'm not in a position to talk about why he [Millard] is in hospital or to comment on his condition.

"Prisons are difficult environments as we've discussed in the past 24 hours and it's a constant process of vigilance and monitoring to ensure we're providing as secure an environment as we can."

There had been at least 13 overdoses of the heroin replacement drug, methadone, at the jail since it began taking prisoners in early 2009 and Mr Rattenbury said authorities were trying to improve ways of governing the medication of detainees.

"I am aware there have been some incidents in the past and these things are a constant process to make improvements to ensure these things are not repeated," he said.

Millard had a long and troubled history of drugs and run-ins with the law. He was jailed in March for a four-hour crime spree in which he stole a car, broke into a home and led police on a daylight pursuit.

He was already paralysed in the left arm, a legacy of a drug overdose last year that left him in intensive care.