RESEARCHERS SURPRISED TO FIND NO LINK BETWEEN MARIJUANA, LUNG CANCER

Study's Findings Apply Even To Heavy Pot Smokers

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 Dr. Donald
Tashkin, a UCLA 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 previously thought.

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 lit 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 studied.

"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 meaning."

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 use in their youth,
when it is most frequently tried.