CANNABIS LINKED TO LUNG CANCER RISK

Cannabis smoking may cause 5 per cent of lung cancer cases in people
up to middle age, according to a New Zealand study which challenges
international thinking on the drug.

Around 15 per cent of New Zealand adults under 46 use cannabis,
drug-use surveys have found.

Researcher Dr Sarah Aldington, of the Medical Research Institute in
Wellington, presented the new case-control study to the Thoracic
Society conference in Auckland yesterday.

Cannabis users may have thought they were safe from lung cancer after
a Californian study of more than 1600 people last year found no link
between the disease and smoking the drug.

Dr Aldington said the evidence on cannabis and the risk of lung cancer
was limited and conflicting.

Her study found the risk rose more than five-fold among the third of
users smoking the most cannabis.

"In conclusion there is a relationship between cannabis smoking and
lung cancer in this study," she said. "Approximately 5 per cent of
lung cancer cases in those aged 55 and under may be attributable to
cannabis..."

This equates to about 15 new cases a year - in 2002, 306 people aged
18-55 were diagnosed with lung cancer in New Zealand.

The study questioned about 60 people with lung cancer from eight
health districts between Waikato and Canterbury and more than 200
"controls" - people randomly selected from electoral rolls in the same
areas.

They were asked about risk factors, including cannabis and tobacco
use.

The researchers calculated that the risk of developing lung cancer
increased by about 8 per cent a year for people whose cumulative
exposure equated to smoking one joint a day. This was about the same
as the increase for someone with a one-pack-a-day tobacco habit.

The younger someone started smoking cannabis, the higher their risk of
lung cancer.

"Long-term cannabis use increases the risk of lung cancer in young
adults, particularly in those who start smoking cannabis at a young
age," the researchers conclude.

Dr Aldington said cannabis was the most commonly used recreational
drug in the world, used by 161 million people, and its use was
increasing in many countries.

She said cannabis contained 50 per cent more cancer-causing chemicals
than tobacco.

The study has found what the University of California researchers had
expected to find but didn't.

A researchers from that study, Dr Donald Tashkin, said in the
Washington Post his group had thought cannabis smokers' deeper
inhalation and tendency to hold smoke in their lungs for longer than
tobacco users would contribute to an increased cancer risk.

He said earlier work had shown cannabis contained cancer-causing
chemicals as potentially harmful as those in tobacco. But cannabis
also contained the chemical THC, which might kill ageing cells and
keep them from becoming cancerous.

Middlemore Hospital clinical director of medicine Associate Professor
Jeff Garrett, a leader of the Thoracic Society, said the Aldington
study was "a good pilot study. It's early work, it's interesting, but
there needs to be more work done."

Drug Foundation executive director Ross Bell was generally sceptical
of the findings as they contradicted most cannabis research he had
read, but he picked up on the increased risk found with starting
young. "We need to be doing things that delay use," he said.

[sidebar]

THE NUMBERS

* Cannabis is used by 161 million people around the
world

* In NZ 5 per cent of lung cancer cases in those aged under 55 may be
due to cannabis smoking.