The meth epidemic sweeping New Zealand is not only causing personal heartache, it's costing the prison service millions.

Photo: juniart

Recent research done by the Department of Corrections suggests more than half of prisoners have used methamphetamine in the lead up to entering prison.

New Zealand's prisons are bursting at the seams, a record 11,000 people are inside and that number continues to grow.

The assistant prison director at Mount Eden, Karen Gillies, said a lot of the central Auckland prison's time and resources go toward dealing with the harm caused by meth.

"It's everything we do, whether it's related to the offending or is the reason that they are here, it goes into every part of the business that we are operating here."

Methamphetamine sentences are on average four years and nine months, and the Department of Corrections said it costs more than $500,000 to house each prisoner during their sentence.

There are 674 offenders in prison for crimes directly related to meth, so for the current cohort of meth producers, sellers and importers in prison, it's costing taxpayers $353 million, just to keep them there.

But Corrections said that's just the obvious cost and doesn't include funds needed for drug treatment services, keeping staff safe from violent users and healthcare.

Apart from the direct drug-related convictions, are the offences committed in order to get meth or while users were high?

Mike, a prisoner at Paremoremo, said he first tried meth the day he got out of prison for his first burglary sentence and meth has been the reason for every one of his offences since.

"And then I ended up in jail three months later for crimes to get meth. I ended up in jail for burglaries back then, but I've been doing home invasions, aggravated robberies, couple of kidnappings, pretty much everything except for murder and rape."

Corrections said it did not hold specific information on how much methamphetamine has contributed to other crime, but it's understood a lot of domestic violence, assaults and armed robberies lead back to the meth trade and meth use.

Its researchers recently took a closer look at meth use by offenders in the year before they were convicted and found that 58 percent of prisoners had used it.

And 70 percent of those users were actually doing time for burglary.

Corrections chief custodial officer Neil Beales said while there are a few factors at play, it's likely that widespread and increasing meth use is contributing to the sharp rise in prisoner numbers in the past few years.

"I don't think any particular study has been done in recent times as to how much of that 25 percent growth that we're seeing in the last three years is directly attributed to meth, but I don't think it would be too shorter line to draw to say that, yes, meth is having an impact."

Corrections said meth is a problem that isn't going to go away and it's now running a meth-specific drug treatment programme called "Meth and Me" to help prisoners.

It's also using that programme to gather much needed information on meth use so it can get a better understanding of exactly what services it needs to provide.

For more on meth and the prison service listen to Insight just after the 8 o'clock news on Sunday Morning and then tune in on air and online on Monday for more of RNZ's Broken Bad investigation into methamphetamine in New Zealand.