NEW YORK (Reuters Health)
- Smoking marijuana can cause changes in lung
tissue that may promote cancer growth, according
to a review of decades of research on marijuana
smoking and lung cancer.
Still, it is not possible
to directly link pot use to lung cancer based on
More than 40 percent of
Americans 12 and older have tried marijuana at
least once, Dr. Reena Mehra of Case Western
Reserve University in Cleveland, Ohio and her
colleagues point out.
"Given the widespread use
of marijuana, its use for what are believed to
be medicinal purposes, and the increasing abuse
and dependence on this substance, it is
important to examine potential adverse clinical
consequences," they write in the Archives of
To investigate whether
marijuana smoking might lead to precancerous
changes in the lungs or lung cancer, Mehra and
her team reviewed 19 studies of the topic.
Analyses of sputum and
lung tissue performed in some of these studies
found more cancer-promoting changes in pot
smokers than in cigarette smokers or
non-smokers, including oxidative stress,
dysfunction of tumor-fighting cells, changes in
tissue structure and DNA alterations, the
However, none of the
studies they analyzed found evidence that
marijuana smoking actually caused lung cancer,
after factoring in the effects of tobacco use.
"We must conclude that no
convincing evidence exists for an association
between marijuana smoking and lung cancer based
on existing data," Mehra and her team write.
Nevertheless, they add,
the precancerous changes seen in studies
included in their analysis -- as well as the
fact that marijuana smokers generally inhale
more deeply and hold smoke in their lungs longer
than cigarette smokers, and that marijuana is
smoked without a filter -- do suggest that
smoking pot could indeed boost lung cancer risk.
It is known, they add, that marijuana smoking
deposits more tar in the lungs than cigarette
The failure to find a
marijuana-lung cancer link may have been due to
methodological flaws in existing research,
rather than the absence of such a link, the
researchers say. Doctors should advise their
patients that marijuana does indeed have
potential adverse effects, they conclude,
including causing precancerous changes in the
SOURCE: Archives of
Internal Medicine, July 10, 2006.