Cannabis linked to lung cancer risk
Herald, March 27, 2007
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
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
Dr Aldington said the evidence
on cannabis and the risk of lung cancer was limited
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
"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 researcher 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
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.
* 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