Decriminalising cannabis would generate money for the Government and ease pressure on New Zealand's courts according to an informal Treasury report.

The documents obtained under the Official Information Act by Nelson lawyer Sue Grey came from an internal Treasury forum "to test policy thinking on a range of issues in the public domain," Finance Minister Bill English said.

The documents reveal Government spends about $400 million annually enforcing prohibition whereas decriminalisation would generate about $150m in revenue from taxing cannabis.

Moreover, it said reforming drug policies would "ease pressure on the justice sector, and lead to fewer criminal convictions for youth and Maori".

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Drug prohibition in New Zealand disproportionately affects males, Maori and youth. In 2001 Maori made up 14.5 per cent of the population but received 43 per cent of convictions for cannabis use.

The report also noted that "drug reform isn't a particularly radical idea these days".

"It's supported by The Economist and the Global Commission on Drug Policy, as well as reports by our Health Select Committee and the Law Commission.

"There are a range of palatable options. Drug use can be kept illegal, satisfying international treaties, but with criminal penalties swapped for civil penalties, like rehabilitation treatment for people who need it."

It noted that Denmark, Germany, Portugal and parts of Australia and the United States had decriminalised cannabis and "don't seem to have increased drug use".

Secretary to the Treasury Gabriel Makhlouf said that while the figures in the report were drawn from "high-level estimates", they were not official Treasury estimates and did not represent a position on drug policy reform.

English added that the documents were "not intended to be distributed more widely than as speaking notes for the forum".

"It was a document prepared by a single staff member for an internal forum and did not come to me."

English declined to comment on whether he had read or considered the document or its recommendations since becoming aware of it.

Sue Grey, whose request made the information public, said that regardless of whether the documents were official advice or not, they proved Treasury had information that drug prohibition cost New Zealand.

"With information comes responsibility.

"[The Government's] main argument is that cannabis presents a huge cost to the community but the report shows the costs are made up of enforcement."

Associate Minister for Health Peter Dunne and Justice Minister Amy Adams declined to comment on how much weight the recommendations made in the report should be afforded.

According to Treasury police spent 600,000 hours on illicit drug enforcement in 2005.

About 6 per cent of cannabis users are caught by police but 95 per cent of those continue to use cannabis.

Rebecca Reider was prosecuted for importing medicinal cannabis products in March.

She said criminal convictions were "a sad rite of passage" for many who use the drug medicinally.

"For some of us getting busted is a sad rite of passage. It's traumatic but it's not going to stop anyone using it.

"From a patient's perspective the numbers that were released to Sue were common sense but it's amazing that someone in the New Zealand government had done those calculations.

"My experience so far has been that everyone is ready for cannabis law reform except the people in government, so I hope putting those figures out there will help."