Taken by An Tran

A 20-year study conducted by scientists from UC San Francisco and the University of Alabama at Birmingham has concluded that the occasional usage of marijuana is not associated with lung damage.

The study, which compared the pulmonary functions of cigarette and marijuana smokers, found the former to be significantly more harmful to an individual’s respiratory system. However, the study results also revealed that high exposure to marijuana smoke eventually leads to the declined functioning of the lungs. The lead author of the study, UCSF Professor Mark Pletcher, commented on the results in a press release, stating, “We found exactly what we thought we would find in relation to tobacco exposure: a consistent loss of lung function with increasing exposure. We were, however, surprised that we found such a different pattern of association with marijuana exposure.”

The study involved the long-term examination of 5,115 individuals, aged 18 to 30, in the United States whose pulmonary functions were routinely tested by means of blowing into a spirometer device. The two variables, the forced expiratory volume (FEV) in the first second of expiration and forced vital capacity (FVC) decreased more prominently among tobacco smokers.

“Essentially with tobacco, the more you use, the more loss you have with both of the indicators, air flow rate and lung volume. There’s a straight-line relationship: The more you use, the more you lose,” explained co-author Stefan Kertesz in an article by the UC Newsroom.

The study authors have noted that a source of the difference stems from the higher rates of usage among tobacco smokers than marijuana smokers. “Tobacco users typically smoke 10 to 20 cigarettes/day, and some smoke much more than that. Marijuana users, on average, smoke only two to three times a month, so the typical exposure to marijuana is much lower than for tobacco,” noted Pletcher.

Still, the rationale of marijuana legalization opponents may not be undermined by the study. As displayed on the website of the National Institute on Drug Abuse, marijuana can still produce adverse effects related to substance abuse, impaired brain development among adolescents and higher susceptibility to mental illnesses including psychosis. Meanwhile, the study findings have reinforced conceptions and prompted a positive response from marijuana advocates even in the midst of the findings regarding decreased pulmonary function associated with high exposure to marijuana—which Pletcher said required a “need for caution and moderation when marijuana use is considered.”

Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws, stated that the findings did not surprise him. He also argued that the negative long-term effects were null since the ingestion and vaporization of marijuana—as opposed to smoking—could overcome the harm from the smoke.

“This study is challenging the preconceived notions we’ve had for some time about the dangers of smoking cannabis and the similarities to smoking tobacco,” stated one UC Berkeley professor in an article by the San Francisco Chronicle. The study was released on Jan. 11 in the Journal of the American Medical Association.