Prison officials are accused of trying to cover up the mistake by telling his mother the prisoner had tried to kill himself, according to documents filed in the ACT Supreme Court.

Christopher Colin Crawford, 26, suffered three heart attacks, severe respiratory distress and psychiatric injury as a result of the incident.

Crawford is still serving a four-year sentence for his part in a violent street robbery that left a man with a fractured skull.

In August 2011, he was on remand in the Alexander Maconochie Crisis Support Unit - a 10-bed facility for mentally ill prisoners at high risk of self-harm - when he suffered a seizure due to a pre-existing medical condition.

An ACT Corrective Services incident report said he requested a drink while he was being treated by Corrections and ACT Health staff and was given a container of juice from the communal refrigerator.

But staff were unaware that the juice belonged to another detainee who had been hoarding prescribed methadone in the container with the intention of overdosing.

Crawford drank two cups of the laced drink before vomiting and collapsing from severe respiratory distress.

Paramedics administered narcan - an antidote to opiate overdose - after the owner of the juice revealed it was laced with methadone.

Crawford's condition stabilised with the treatment, but he was taken to Canberra Hospital when he again deteriorated about 6.30pm.

Court documents say he suffered three cardiac arrests and psychiatric injury from drinking the toxic liquid.

Through lawyers Ken Cush and Associates, Crawford alleges staff lied to his mother by saying he had deliberately overdosed on methadone in an attempt to end his life.

Crawford's legal team claims prison authorities had breached their duty of care owed to the detainee in nine areas, including failing to maintain safe systems for the control of dangerous substances such as methadone and failure to follow proper guidelines for the dispensing of the drug.

"The [ACT government] failed to initiate and maintain a safe system of accounting for and dispensing dangerous drugs such as methadone," the statement of claims reads.

"Its servants … lied to [Crawford's] mother, telling her that [her son] had deliberately ingested the methadone so as to end his own life when in fact they knew [he] had not deliberately ingested methadone.

"And that methadone was administered to [Crawford] by centre staff as a consequence of their failure to initiate and maintain a safe system for accounting for and dispensing methadone warranting an award of exemplary and aggravated damages."

The court documents note no claim for economic loss is made.

The lawsuit was served to the government via post last week and Fairfax Media understands it has not had time to file a defence.