Often, when people hear about the studies which have shown that smoking marijuana doesn’t cause lung cancer, they’ll say something like, “Well, inhaling any smoke, cancer or not, is bound to cause some breathing problems.” Guess what? It doesn’t do that, either.
A report published last year in the Journal of the American Medical Association shows that — over a 20-year period — marijuana smokers generally did not experience a loss in lung function. In fact, many actually had enhanced lung capacity, which one researcher speculated might come from the practice of “deep-lunging” hits to maximize their intoxicating effects.
Whatever the cause, the fact remains that the study showed the lung function of most marijuana smokers actually improved slightly over time.
A healthy adult man can exhale about a gallon of air in a second, according to researcher Stefan Kertesz, M.D., an assistant professor of medicine at the University of Alabama at Birmingham.
But cannabis smokers, on average, were able to blow out that gallon of air plus about 50 milliliters.
The average number of times marijuana users in the study said they smoked was two to three times per month — but even in regular users, researchers said they still saw no evidence of breathing problems.
In fact, researchers estimated that lung capacity would stay slightly larger even if a person had smoked a joint a day for seven years, or two or three joints a day for three years.
Kertesz said the study should reassure people who smoke marijuana for medical reasons.
”This is a well-designed, well-described study,” said Jeanette M. Tetrault, M.D., an assistant professor of medicine at Yale School of Medicine in New Haven, Connecticut.
Researchers said this “lung-stretching” property of cannabis may be due to the way people smoke marijuana — by taking and holding deep breaths with smoke — than it does with any actual benefit of marijuana itself.
The study didn’t have a lot of light to shed on heavy smokers — those who smoked the equivalent of a joint a day for 40 years, or smoked more than 25 times a month — because the number of such users in the study was small, and the scientists weren’t sure if a possible trend indicating slight lung irritation from heavy smoking was valid or not.
There is, however, another study — the largest of its kind ever conducted, in fact, by Dr. Donald Tashkin of the University of California at Los Angeles (UCLA) — which shows that marijuana smoking, even heavy, long-term smoking, does not lead to lung cancer.
Tashkin, medical director of the pulmonary function laboratory at the David Geffen School of Medicine at UCLA, who has spent his career studying the health effects of marijuana, said the new study is helpful because it was relatively large and followed people for a long time, which gives him confidence in the results.
“The main thrust of the paper has confirmed previous results indicating that marijuana in the amounts in which it is customarily smoked does not impair lung function,” he said.
His own study of heavy, habitual marijuana smokers — people who smoked the equivalent of a joint a day for 50 years — found no harmful effect on lung function.
Tobacco’s Another Story
Tobacco smokers, on the other hand, were found to have less capacity in the amount of air they could exhale, and also in the speed at which they could empty air from the lungs. Cigarette smokers in the study saw their lung function drop steadily over the entire 20 years.
The study included more than 5,000 people in the United States. They were studied between 1986 and 2006.
“Marijuana may have beneficial effects on pain control, appetite, mood and management of other chronic symptoms,” researchers from the University of Alabama, the University of California, and Northwestern University said in a statement.
“Our findings suggest that occasional use of marijuana for these or other purposes may not be associated with adverse consequences on lung function [emphasis added],” the researchers said.
Over the 20-year period, researchers repeatedly checked two measures of lung function, reports Brenda Goodman at WebMD. One was a test that measured the amount of air forcefully exhaled in a single second; the second test measured the total amount of air exhaled after taking the deepest possible breath.
These tests help doctors diagnose chronic, irreversible breathing problems like chronic obstructive pulmonary disease (COPD).
Cigarette smoking is a leading cause of COPD; researchers expected marijuana to irritate the lungs in a similar fashion, since it contains many of the same chemicals as tobacco smoke. But crucially, the cannabinoids in marijuana smoke seem to protect the lungs and pulmonary passageways from both irritation and from cancer.