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Heavy cannabis use could be a cause of Maori having the world's highest lung cancer rate, ground-breaking research suggests.

Many Maori, from children to kaumatua, use cannabis in "epidemic proportions", says a study by Professor Richard Beasley of the Medical Research Institute in Wellington.

But cannabis might not be as safe as the proponents of its legalisation say.

A paper by Professor Beasley on the health effects of cannabis was among research that prompted Wellington coroner Garry Evans last week to urge that Government policy on illicit drugs be changed from "harm minimisation" to campaigning against drug use.

The paper reviews the literature on cannabis and suggests it is more cancer-causing than tobacco and, like tobacco, causes bronchitis.

Professor Beasley said that his institute was close to finishing what he believed was the world's first study on links between cannabis and lung cancer.

The study reviews all lung cancer cases from Hamilton to Canterbury with a focus on whether the sufferer used cannabis. A tandem study is tracking 300 New Zealanders in four groups of 75 to find the effects on lungs of cannabis smoking.

One group consists of cannabis smokers only, another smokes cannabis and tobacco, the third tobacco only and the fourth is made up of non-smokers.

In his paper for the coroner, Professor Beasley said information was urgently needed on the potential role of marijuana in New Zealand's high lung cancer rate, particularly among Maori, who had the world's highest rate and were heavy cannabis users.

Research showed cannabis use had reached epidemic proportions and was rising.

The proportion of the population to have tried it went from 43 per cent in 1990 to 52 per cent by 1998 and the proportion of regular users from 18 per cent to 21 per cent.

Studies showed regular smokers of three to four cannabis joints a day had chronic bronchitis and other symptoms similar to those of smokers of 20 or more tobacco cigarettes a day.

"There is a perception that we understand the risks [of illicit drug use], but our research shows we don't know all the effects at all," Professor Beasley said.

The institute also hoped to conduct research into so-called party pills.

Inside dope

* Smoking three cannabis cigarettes a day is equal to more than 20 tobacco cigarettes

* Maori lung cancer rates may be linked to regular cannabis use

* Research suggests cannabis use had reached epidemic proportions and is tolerated among Maori

- NZPA