Pubdate: Fri, 02 Aug 2013
Source: National Post (Canada)
Copyright: 2013 Canwest Publishing Inc.
Contact: http://drugsense.org/url/wEtbT4yU
Website: http://www.nationalpost.com/
Details: http://www.mapinc.org/media/286
Author: Tom Blackwel

SKEPTICS SNUB STUDY LINKING POT, LUNG CANCER

Canadian-Led Research Suggests Risk Doubles

Relatively heavy smoking of marijuana may as much as double the risk 
of someone contracting lung cancer, suggests a new, Canadian-led 
study that adds nuance to the debates over medical marijuana and 
outright legalization.

The study, which contradicts other recent research that concluded the 
connection was all but non-existent, looked at a large group of 
Swedish men who were surveyed about their lifestyles in 1969-70, then 
tracked over the subsequent 40 years. Those classified as "heavy" pot 
users when young were more than twice as likely to have lung cancer 
by 2009, the researchers - Russ Callaghan, a psychiatry professor at 
the University of Northern British Columbia, and colleagues in Russia 
and Sweden - found.

Mr. Callaghan said he does not want to "demonize" marijuana, noting 
that two legal drugs, tobacco and alcohol, unquestionably cause 
"dramatically" more harm.

But it is important to get to the bottom of its possible negative 
effects as well as potential benefits, he said. "It is seen as 
organic and natural," he said. "[The study] does add one piece of 
evidence to suggest a caution around that."

Other leading scientists in the field, however, say the nature of the 
data used in the new research, published in the journal Cancer Causes 
and Control, makes its findings suspect. Much more convincing 
evidence was analyzed recently by the International Lung Cancer 
Consortium, asserted Hal Morgenstern, a University of Michigan 
epidemiologist and part of that group. The consortium scrutinized 
results from six "case control" studies that compared 2,100 cancer 
patients and 3,000 healthy controls, finding no significant link 
between marijuana and malignancy, the scientists told a conference in April.

Though marijuana smoke does contain cancer-causing chemicals, the 
majority of people simply don't consume enough of it to get ill, said 
Mr. Morgenstern.

"When you think about people smoking 20-40 cigarettes a day for 40 
years, they're smoking hundreds of thousands of cigarettes," he said. 
"The exposure [to harmful smoke] that marijuana users get ... is more 
than a magnitude of difference less."

There are reasons to fear that smoking pot might lead to cancer, 
including the fact it contains some of the same carcinogens as 
tobacco, tends to be inhaled more deeply and generally is smoked 
without a filter.

Meanwhile, use of medical marijuana is increasingly popular, with 
varying amounts of evidence suggesting it can help alleviate 
chemotherapy-related nausea, some forms of pain and loss of appetite 
in cancer patients.

The international lung cancer consortium is not alone in dismissing 
the danger of a cancer connection. A similar review published in 
February by Donald Tashkin, a medical professor at the university of 
California at Los Angeles, found no association between cancer and 
low-to-moderate marijuana smoking, and mixed evidence on heavy, long-term use.

Dr. Callaghan said he and colleagues used the Swedish data because it 
provides a particularly comprehensive picture of the health of its 
subjects. They looked at 49,000 men conscripted into the army in 
1969-70 and subjected to extensive testing and surveys at the time - 
including questions about cannabis use - and tracked them through 
various health registries as they aged.

After filtering out the effects of smoking, alcohol consumption, 
respiratory disease and socio-economic status, the researchers found 
that those who had reported using pot at least 50 times by 1970 were 
more than twice as likely to have contracted lung cancer by 2009.

The researchers admit the study could not trace how much the men used 
marijuana or tobacco after the initial interviews. They speculate 
that similar patterns would have continued through their 20s and 30s.

Mr. Morgenstern said it is also possible, though, those individuals 
who contracted cancer and who had been heavy pot smokers when young 
switched to cigarettes later, meaning the tobacco, not marijuana, 
made them sick.

In fact, pot leads to "far less" dependency than does tobacco, noted 
Dr. Tashkin in an email interview.

The Canadian-Swedish study, with 49,000 participants, sounds large, 
but the sample included only 189 lung cancer patients, he added. The 
"case-control" studies the consortium analyzed involved interviewing 
thousands of cancer patients and healthy people about their marijuana 
use, making the findings more statistically powerful, he argued.
- ---
MAP posted-by: Jay Bergstrom