Methamphetamine, cannabis, ecstasy, heroin and alcohol — these are some of the drugs New Zealand inmates have tested positive for in the last two years.

But Corrections says the number of prisoners caught using drugs is falling and it is constantly looking for new ways to detect contraband before it gets behind the perimeter fence.

In 2015 and 2016, Corrections randomly drug tested 16,719 inmates.

Of those, 1179 were found to have a drug — or a combination of drugs — in their system.

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While some tested positive for substances found in medication provided by prison medical staff, most of the results showed cannabis or amphetamine-type stimulants (ATS).

The stimulants include methamphetamine and ecstasy.

Of the 1179 inmates who tested positive, 36 were women.

The names of prisoners subject to drug testing are randomly selected on a weekly basis.

Alongside ATS and cannabis, the drugs used also included opiates — generally opium, heroin, morphine, methadone, codeine and pethidine — benzodiazepines and alcohol.

Benzodiazepines — including diazepam and lorazepam — are generally prescription drugs used to treat conditions such as anxiety and sleep problems.

Corrections acting national commissioner Rachel Leota said there was zero tolerance for contraband — encompassing drugs and drug paraphernalia, alcohol, communication devices, tattoo equipment and weapons — in New Zealand prisons.

Leota said prisoners had a vast number of ways of getting contraband into prison, such as concealment in vehicles and produce, internal concealment on an offender's body, concealment in mail and in items thrown over fences or smuggled in by prisoners' visitors.

"Over the past decade we have a high success rate of detecting contraband," she said.

"In 2016/17 Corrections conducted approximately 8000 drug tests in prisons; just 3.6 per cent of the general random drug tests ... returned a positive result; compared to 2010/2011 when the rate was 6.8 per cent".

Leota said most cases were dealt with through the internal misconduct system.

However, prisoners can also be prosecuted under the Corrections Act 2004.

Leota said Corrections staff use a range of screening measures to prevent contraband entering prisons and are "constantly working to identify and mitigate risk areas in the physical environment and stay informed about new methods of concealment in order to maintain our high success rate in detecting contraband."