Almost 30 per cent of inmates at the Alexander Maconochie Centre reported using heroin inside the prison in 2016, amid an ongoing culture of detainee drug-seeking and seeming easy access to the centre's methadone program.
The findings are part of an investigation into the prison's opioid replacement therapy program by ACT Health Services Commissioner Karen Toohey, sparked by Phillip Moss' independent inquiry into the death in custody of Steven Freeman in 2016.
It is one of a series of Legislative Assembly committee inquiries, Auditor-General investigations and reports by independent consultants that raised similar concerns about the prison's methadone program over several years.
The commissioner's investigation did not look at the specific circumstances surrounding Mr Freeman's death, or the death in custody of Mark O'Connor in the prison last year, both of which are currently the subject of coronial inquests.
Ms Toohey's inquiry found that while "significant improvements" had been made to the opioid replacement therapy program in the AMC since Mr Freeman's death, more needed to be done and some existing policies were not being fully enforced.
It also found inmates and staff maintained the view there was a "culture of drug seeking" among inmates and that it was relatively easy for some to get on the methadone program, which some were doing for "recreation".
The commissioner made 16 key recommendations to improve the rigour and consistency of decision-making on induction and assessment to reduce the chances of inmates been prescribed methadone when not genuinely opioid-addicted.
"Further action is needed to minimise risks of diversion of methadone, and to ensuring that the particular needs of Aboriginal and Torres Strait Islander detainees are met in the provision of health services at the AMC," she said.
The recommendations also included better assessment of inmates before putting them on methadone, more staff training and strengthening efforts to prevent diversion of drugs to non-prescribed inmates.
The investigation reviewed clinical files for 20 inmates inducted on the program from April to October last year, none of which had any evidence urine testing was undertaken to corroborate inmates' claims of opioid-dependency.
It also found little evidence justice health workers tried to corroborate such claims with inmates' community general practitioners or the Winnunga Nimmityjah Aboriginal Health Service.
The commissioner also found no evidence of any individual case plans for indigenous inmates, as required by the ACT's opioid treatment guidelines, or cultural supports being sought for those detainees
It also found that despite new electronic iris-scanning "idose" machines operating at the prison since last August - which would make for safer dosing practices - one inmate overdosed on the drug as recently as February this year.
That inmate had sought out a dose of methadone outside of the usual dosing period, and while the machine was off, staff instead gave the inmate a manual dosing, leading to an overdose which the inmate later recovered from.
The commissioner also recommended improving Throughcare practices for opioid-dependant inmates leaving the prison, ensure all indigenous inmates are offered annual health check ups and that the justice directorate work harder to progress a needle syringe program at the prison.
The report also cited the latest ACT Health Detainee Health and Wellbeing Survey, which was completed in 2016 but not publicly released, which found 29 per cent of inmates at the prison had used heroin while in the prison.
That survey also found 55 per cent of detainees reported having ever used heroin, with 35 per cent reporting injecting illicit drugs once a day or more in the four weeks prior to incarceration.
The survey, the commissioner's report shows, also found 19 per cent of detainees had used other opiates while in prison and up 19 per cent reported injecting drugs in the AMC.
Ms Toohey's report also cited the high rate of inmates on the official methadone program, at 30 per cent compared to the national rate of five per cent, though comparisons are difficult given varied practices from one jurisdiction to another.
The report also showed existing policies for preventing of 'diversion' - when a prescribed inmate passes the drug on to another - were not being followed rigorously, including allowing inmates to take a dose while wearing coverings such as hoods or items that could have obscured containers.
Ms Toohey recommended the existing policy be enforced and staff be provided more training to ensure it was adhered to.
The commissioner will be working with justice health and corrective services to ensure changes implemented are maintained and continue to improve health services at the AMC.