The number of drug users being locked up in Queensland prisons is pushing the system to breaking point, according to a major inquiry, which finds society receives little in return for the $107,000 it costs to keep each offender behind bars for a year.

Key points: In the past five years, Queensland's prisoner population has jumped from 6,079 to 9,021

In the past five years, Queensland's prisoner population has jumped from 6,079 to 9,021 That's about 2,000 inmates more than what the state's jails are designed to hold

That's about 2,000 inmates more than what the state's jails are designed to hold An inquiry recommends changing the status of certain drug crimes so they don't lead to jail time

More people are being sent to prison now than at any time in the past 120 years — despite crime rates being on a steady decline.

That is one of the findings of the Queensland Productivity Commission, which was asked by the Palaszczuk Government to work out what was causing the surge of people in the state's prisons.

The commission also found that locking up drug users was often a waste of time and money, and recommended that some drug offenders be kept out of the prison system.

In the past five years alone, the inmate population has jumped from 6,079 to 9,021 — more than 2,000 beyond what the state's jails are designed to hold.

One in three of those extra prisoners went to jail on drug charges.

Richard Smyth, 47, is one of them.

Beyond the brink and back again

The former landscaper was jailed for four-and-a-half years in 2016 on two high-level drug possession charges.

He served 18 months in Borallon prison outside Ipswich.

He is now clean and living on the Sunshine Coast.

But he said incarceration was a long way from rehabilitation.

Mr Smyth served 18 months in jail for drug possession and is now clean. ( ABC Sunshine Coast: Owen Jacques )

He told of inmates "shooting up" in prison, and of easy access to drugs for those who want them.

"It's readily available," he said.

What you need to know: Queensland is locking up more people now than any time since 1900

Queensland is locking up more people now than any time since 1900 One in three of those extra prisoners were convicted for drug offences

One in three of those extra prisoners were convicted for drug offences The QPC draft report finds the benefits of locking up drug offenders is not worth the cost

The QPC draft report finds the benefits of locking up drug offenders is not worth the cost It recommends drug offences be dropped from the Criminal Code

It recommends drug offences be dropped from the Criminal Code Every prison in Queensland is overcrowded, and each inmate costs $107,000 a year to keep behind bars

Every prison in Queensland is overcrowded, and each inmate costs $107,000 a year to keep behind bars By 2025, the Queensland Government would need to spend $6.5 billion on prisons just to keep up Queensland Productivity Commission's Inquiry into Imprisonment and Recidivism, draft report

He said the level of overcrowding, even three years ago, meant there were not enough drug rehabilitation programs for inmates who needed them.

Once released, he had nowhere to go and was suddenly homeless.

Mr Smyth was no longer using ice and found a friend to stay with.

For other inmates, that can mean re-entering the same world of illicit drug use that put them into prison.

"You come out of jail and it's very hard to get a place to stay. So people go and stay with the people that they're with before — so you just you go back into that same environment," Mr Smyth said.

Of the 1,000 prisoners released from Queensland jails each month, half return to prison or community supervision within two years.

The commission recommends changing the status of certain drug, public nuisance and other minor crimes. They would remain illegal, but would not lead to jail time.

The reforms would focus on crimes "for which the benefits [of jail] do not outweigh the costs" and which "do not have an obvious victim".

'Brutal and alien': Are prisons making better criminals?

Together Union's Michael Thomas represents Queensland prison officers at a particularly dangerous time.

In the past 12 months, two workers have been violently attacked while on the job: one at Woodford prison on the Sunshine Coast late last year, and another last month at Wolston jail, south of Brisbane.

Mr Thomas said prisons were alien and brutal places, and that some minor criminals would become more dangerous by being inside.

Michael Thomas warns prisons are overcrowded and officers' lives are at risk. ( ABC News: Mark Leonardi )

"What we're doing is introducing them to more people that may fundamentally change the direction of their life in a way that puts the community at risk.

"If we're incarcerating the wrong people, what we are effectively doing is training better criminals."

He said the overcrowding meant there were multiple people in cells designed for one and that was causing more assaults and "standover tactics".

Mr Thomas also conceded drugs were coming in and circulating through prisons, despite the best efforts of staff.

'This is not a war on drugs. It's a war on drug users'

Marion McConnell's son died from a heroin overdose in the early 1990s.

The Canberra mum helped found Families and Friends for Drug Law Reform — a group that brings together those who have loved ones beset by drug addiction.

Marion McConnell's son died from a heroin overdose in the 1990s. ( ABC News: Greg Nelson )

She said in the 25 years since the group's founding, the so-called war on drugs had not only failed, but the drugs had become even more dangerous.

"It's many, many, many times worse," she said.

"Back when our group started, heroin was the main drug. And there were treatments for heroin addiction.

"Now we have so many synthetic drugs, and we can buy drugs on the internet. It's a much worse situation we have now because we didn't do what we could have done 25 years ago."

Head of the Queensland Network of Alcohol and Other Drug Agencies, Rebecca Lang, said any war on drugs had failed and that they were now more powerful, cheaper and more widely available than ever before.

"It seems we've got 30 years' worth of evidence now that demonstrates that, so it's time to try something different," she said.

Drug expert Rebecca Lang says it's time for the laws to change. ( ABC News: Elizabeth Pickering )

Ms Lang works alongside drug rehabilitation and support groups and said if the state spent more on treating drug users instead of locking them up, it would make an "astounding" difference.

"We're already paying for the costs of people who have drug problems," she said.

"But if we invest in treatment, what we're actually doing is getting to the source of the problem."

What will it cost if nothing changes?

Corrective Services Minister Mark Ryan said the Queensland Government was spending $861 million to address overcrowding.

It is expanding the Capricornia Correctional Centre near Rockhampton and building a new prison outside Gatton west of Brisbane.

He said the two projects would deliver 1,300 extra beds.

That is about 800 beds short of what's needed today, according to Queensland Productivity Commission data.

Mr Ryan said there would be an extra 4,000 beds for inmates by 2023.

The commission warns that if the state maintains a business-as-usual approach to locking people up, it would need to spend up to $6.5 billion on building almost 6,000 more cells by 2025.

That is the equivalent of $1,300 for every man, woman and child in Queensland.

The commission is due to release its final report in August.

Mr Smyth said regardless of its findings, something had to change.

"Is putting people in jail, is that rehabilitating people?" he asked.

"No, clearly not if you're reoffending."