CHICAGO (AP) — Smoking a joint once a week or a bit more apparently doesn't
harm the lungs, suggests a 20-year study that bolsters evidence that marijuana
doesn't do the kind of damage tobacco does.
The results, from one of the largest and
longest studies on the health effects of marijuana,
are hazier for heavy users — those who smoke two or more joints daily for
several years. The data suggest that using marijuana that often might cause a
decline in lung function, but there weren't
enough heavy users among the 5,000 young adults in the study to draw firm
conclusions.
Still, the authors recommended "caution and moderation when marijuana
use is considered." Marijuana is an illegal drug under federal law although some states allow
its use for medical purposes.
The study by researchers at the University of California, San Francisco, and the University of Alabama at Birmingham was released Tuesday
by the Journal of the American Medical Association.
The findings echo results in some smaller
studies that showed while marijuana contains some of the same toxic chemicals
as tobacco, it does not carry the same risks for lung disease.
It's not clear why that is so, but it's
possible that the main active ingredient in marijuana, a chemical known as THC,
makes the difference. THC causes the "high" that users feel. It also
helps fight inflammation and may counteract the effects of more irritating
chemicals in the drug, said Dr. Donald Tashkin,
a marijuana researcher and an emeritus professor of medicine at the University of California, Los Angeles. Tashkin was not
involved in the new study.
Study co-author Dr. Stefan Kertesz said there are other aspects of
marijuana that may help explain the results.
Unlike cigarette
smokers, marijuana users tend to breathe in deeply when they inhale a
joint, which some researchers think might strengthen lung tissue. But the
common lung function tests used in the study require the same kind of deep
breathing that marijuana smokers are used to, so their good test results might
partly reflect lots of practice, said Kertesz, a drug abuse researcher and
preventive medicine specialist at the Alabama university.
The study authors analyzed data from participants in a 20-year federally
funded health study in young adults that began in 1985. Their analysis was
funded by the National Institute on Drug Abuse.
The study randomly enrolled 5,115 men and
women aged 18 through 30 in four cities: Birmingham, Chicago, Oakland, Calif.,
and Minneapolis. Roughly equal numbers of blacks and whites took part, but no
other minorities. Participants were periodically asked about recent marijuana
or cigarette use and had several lung function tests during the study.
Overall, about 37 percent reported at
least occasional marijuana use, and most users also reported having smoked
cigarettes; 17 percent of participants said they'd smoked cigarettes but not
marijuana. Those results are similar to national estimates.
On average, cigarette users smoked about
9 cigarettes daily, while average marijuana use was only a joint or two a few
times a month — typical for U.S. marijuana users, Kertesz said.
The authors calculated the effects of
tobacco and marijuana separately, both in people who used only one or the
other, and in people who used both. They also considered other factors that
could influence lung function, including air pollution in cities studied.
The analyses showed pot didn't appear to
harm lung function, but cigarettes did. Cigarette
smokers' test scores worsened steadily during the study. Smoking
marijuana as often as one joint daily for seven years, or one joint weekly for
20 years was not linked with worse scores. Very few study participants smoked
more often than that.
Like cigarette smokers, marijuana users
can develop throat irritation and coughs, but the study didn't focus on those.
It also didn't examine lung cancer, but other studies haven't found any
definitive link between marijuana use and cancer.
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Source: Online
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