Marijuana Not as Damaging to Lungs as Tobacco

Marijuana contains many of the irritating chemicals found in tobacco, but smoking it occasionally does not result in long-term loss of lung function, a recent study indicates. Heavy use, however, did result in significant damage.

“With marijuana use increasing and large numbers of people who have been and continue to be exposed, knowing whether it causes lasting damage to lung function is important for public-health messaging and medical use of marijuana,” said the study’s senior author, Stefan Kertesz, MD, an associate professor in the division of preventive medicine at the University of Alabama at Birmingham, in a press release.

The researchers used data from the Coronary Artery Risk Development in Young Adults (CARDIA) study, which regularly measured pulmonary function and gathered information on smoking patterns from 5,115 subjects over the course of two decades starting in 1985.

The data revealed that nearly as many participants were exposed to marijuana smoke as to tobacco smoke. However, marijuana use was relatively infrequent (two to three episodes per month on average) compared with tobacco use (eight to nine cigarettes per day on average).

The more tobacco a participant smoked, the lower their pulmonary function was as measured by forced expiratory volume in the first second of expiration (FEV₁) and forced vital capacity (FVC). However, those with low levels of exposure to marijuana actually had increased levels of FEV₁ and FVC, though as exposure grew very heavy these levels began to decline.

“Those increases [in pulmonary function] were not large, but they were statistically significant,” Kertesz said in the release. “And the data showed that even up to moderately high-use levels—one joint a day for seven years—there is no evidence of decreased air-flow rates or lung volumes.”

Kertesz cautioned that the study results do not indicate that marijuana is a healthy habit. “Marijuana is still an illegal drug, and it has many complicated effects on the human body and its function,” he said. “In our findings we see hints of harm in pulmonary function with heavy use, and other studies have shown that marijuana use increases a user’s likelihood of a heart attack, according to the American Heart Association, and impairs the immune system's ability to fight disease, according to the National Institute on Drug Abuse.”

The study was published in the January 11 edition of the Journal of the American Medical Association.