Popular drugs among inmates are understood to include pregabalin, a prescription medication used to treat epilepsy and nerve pain, and quetiapine, an antipsychotic medication for schizophrenia and bipolar disorder.

Prescription medications are typically easier to access compared with illicit drugs such as heroin or methamphetamine, and can be used as a kind of black market currency among inmates.

The emergence of pregabalin, marketed under the brand name Lyrica, has been well documented inside British prisons, with the British Medical Association last year calling for it to be made a controlled substance.

A study in 2008 found that quetiapine, marketed under the brand name Seroquel, was prone to abuse inside American prisons.

Other contraband prescription medications listed on AMC search registers dating back to 2013 include mirtazapine, an anti-depressant, and fluvoxamine, which is used to treat obsessive-compulsive disorder among other things.

In 2016-17 there were 146 separate medication seizures made inside the prison, or an average of a seizure every two and a half days.

These included properly prescribed medications that had been stockpiled, as well as expired medications, a spokesman for the territory's justice directorate said.

"The medications range from drugs that would be available over the counter in the community (paracetamol) through to pharmacy or prescription medications.

"Notwithstanding the efforts of ACT Corrective Services and partner agencies, it remains the unfortunate case that contraband, including illicit substances, still enters the AMC ... this is not unique to the ACT."

In comparison, cannabis was confiscated 20 times in 2016-17, methamphetamine was confiscated nine times and heroin was confiscated twice.

The total number of confiscations was slightly down from 2015-16, when there were 152 medication seizures at the AMC.

A justice directorate spokesman said there had been no noticeable upward trend in the amount of contraband medication, which had always comprised a significant proportion of seizures.

Throughout the month of May last year officers seized 42 items of contraband medication, including mirtazapine, zyprexa and fluvoxamine.

One inmate was found to be hoarding 48 tablets of fluvoxamine, which can cause agitation, insomnia and, in rare cases, hallucinations.

The Penington Institute, a not-for-profit organisation that researches substance abuse issues, has previously researched wider issues around drug use inside Australian prisons.

"There is no doubt that prescription medicines are prevalent in our prisons," chief executive John Ryan said.

"Unfortunately, prescription drug abuse is a growing problem in Australia and our prisons are the perfect environments to fuel any sort of substance misuse."

Prescription drugs were also popular because they could be traded for other contraband prison commodities such as cigarettes, Mr Ryan added.

Mr Ryan said it was vital prisons offered drug-treatment programs that went beyond merely prescribing medication to treat an issue, and applauded the work of the ACT government in this space.

"The Alexander Maconochie Centre in the Australian Capital Territory is a great example of what can be done [in terms of drug treatment]," Mr Ryan said.

Over the Christmas period two inmates, including a convicted murderer, were taken to hospital after overdosing inside the prison.

"The prescription drugs are getting more and more popular with buprenorphine and ice being rampant," said one prison source following the overdoses.

Buprenorphine, like methadone, is a synthetic drug used to treat opiate addiction by preventing withdrawal and lowering cravings.

A justice directorate spokesman said there had been an increased volume of contraband found inside the prison throughout November and December last year.

A spokesman for ACT Health has previously said there had been three detainee overdoses in total throughout December.

"ACT Health is unable to specifically identify the medications that were involved in these three incidents due to the fact that the small number of incidents may potentially identify detainees."