Study finds no marijuana-lung cancer link
California (Reuters) -- Marijuana smoking does not
increase a person's risk of developing lung cancer,
according to the findings of a new study at the
University of California Los Angeles that surprised
even the researchers.
had expected to find that a history of heavy
marijuana use, like cigarette smoking, would
increase the risk of cancer.
Instead, the study,
which compared the lifestyles of 611 Los Angeles
County lung cancer patients and 601 patients with
head and neck cancers with those of 1,040 people
without cancer, found no elevated cancer risk for
even the heaviest pot smokers. It did find a 20-fold
increased risk of lung cancer in people who smoked
two or more packs of cigarettes a day.
The study results
were presented in San Diego Tuesday at a meeting of
the American Thoracic Society.
The study was
confined to people under age 60 since baby boomers
were the most likely age group to have long-term
exposure to marijuana, said Dr. Donald Tashkin,
senior researcher and professor at the UCLA School
The results should
not be taken as a blank check to smoke pot, which
has been associated with problems including
cognitive impairment and chronic bronchitis, said
Dr. John Hansen-Flaschen, chief of pulmonary and
critical care at the University of Pennsylvania
Health System in Philadelphia. He was not involved
in the study.
showed marijuana tar contained about 50 percent more
of the chemicals linked to lung cancer, compared
with tobacco tar, Tashkin said. In addition, smoking
a marijuana joint deposits four times more tar in
the lungs than smoking an equivalent amount of
"Marijuana is packed
more loosely than tobacco, so there's less
filtration through the rod of the cigarette, so more
particles will be inhaled," Tashkin said in a
statement. "And marijuana smokers typically smoke
differently than tobacco smokers -- they hold their
breath about four times longer, allowing more time
for extra fine particles to deposit in the lung."
He theorized that
tetrahydrocannabinol, or THC, a chemical in
marijuana smoke that produces its psychotropic
effect, may encourage aging, damaged cells to die
off before they become cancerous.
cautioned a cancer-marijuana link could emerge as
baby boomers age and there may be smaller population
groups, based on genetics or other factors, still at
risk for marijuana-related cancers.