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Largest Cannabis study ever concludes herb not harmful
- The largest study of its kind has unexpectedly concluded that smoking
marijuana, even regularly and heavily, does not lead to lung cancer.
The new findings "were against our expectations," said Donald Tashkin
of the University of California at Los Angeles, a pulmonologist who has
studied marijuana for 30 years.
"We hypothesized that there would be a positive association between
marijuana use and lung cancer, and that the association would be more
positive with heavier use," he said. "What we found instead was no
association at all, and even a suggestion of some protective effect."
Federal health and drug enforcement officials have widely used
Tashkin's previous work on marijuana to make the case that the drug is
dangerous. Tashkin said that while he still believes marijuana is potentially
harmful, its cancer-causing effects appear to be of less concern than
Earlier work established that marijuana does contain cancer-causing
chemicals as potentially harmful as those in tobacco, he said. However,
marijuana also contains the chemical THC, which he said may kill aging
cells and keep them from becoming cancerous.
Tashkin's study, funded by the National Institutes of Health's National
Institute on Drug Abuse, involved 1,200 people in Los Angeles who had
lung, neck or head cancer and an additional 1,040 people without cancer
matched by age, sex and neighborhood.
They were all asked about their lifetime use of marijuana, tobacco and
alcohol. The heaviest marijuana smokers had lighted up more than 22,000
times, while moderately heavy usage was defined as smoking 11,000 to
22,000 marijuana cigarettes. Tashkin found that even the very heavy
marijuana smokers showed no increased incidence of the three cancers
"This is the largest case-control study ever done, and everyone had to
fill out a very extensive questionnaire about marijuana use," he said.
"Bias can creep into any research, but we controlled for as many
confounding factors as we could, and so I believe these results have real
Tashkin's group at the David Geffen School of Medicine at UCLA had
hypothesized that marijuana would raise the risk of cancer on the basis of
earlier small human studies, lab studies of animals, and the fact that
marijuana users inhale more deeply and generally hold smoke in their
lungs longer than tobacco smokers -- exposing them to the dangerous
chemicals for a longer time. In addition, Tashkin said, previous studies
found that marijuana tar has 50 percent higher concentrations of chemicals
linked to cancer than tobacco cigarette tar.
While no association between marijuana smoking and cancer was found,
the study findings, presented to the American Thoracic Society
International Conference this week, did find a 20-fold increase in lung cancer
among people who smoked two or more packs of cigarettes a day.
The study was limited to people younger than 60 because those older
than that were generally not exposed to marijuana in their youth, when it
is most often tried.
420 Times Magazine
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