Smoking marijuana in combination with cigarettes may cause greater damage to the lung alveoli, according to research presented today at the annual meeting of the Radiological Society of North America (RSNA).
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It is commonly believed that smoking marijuana is not harmful to the lungs. There is a large body of established research identifying the harms of smoking. In contrast, very little is known about the effects of smoking marijuana, and even less research has been done on the combined effects of smoking marijuana and cigarettes.
"Marijuana is the most widely used illicit psychoactive substance in the world, and its use has increased in Canada since legalization for non-medicinal purposes in 2018," said study co-author Jessie Kang, MD, a cardiothoracic radiologist and assistant professor in the Department of Diagnostic Radiology at Dalhousie University in Halifax, Nova Scotia, Canada. "Currently, there isn’t much research on the effects of marijuana use on the lungs."
To determine the effects of smoking marijuana and cigarettes, researchers in the multicenter prospective study examined chest CT images of four groups of patients: nonsmokers, cigarette smokers, marijuana smokers, and combined marijuana and cigarette smokers. The marijuana smokers included in the study had smoked marijuana at least four times a month for two years. Patients who ingested marijuana in the form of edibles or oral drops were excluded from the study.
The researchers found that people who combined marijuana and cigarettes were 12 times more likely to have centrilobular emphysema than non-smokers. Centrilobular emphysema is a type of pulmonary emphysema in which the air sacs inside the lungs are damaged. This can cause breathing difficulties and other serious respiratory symptoms.
Figure : Pulmonary emphysema in marijuana and tobacco smokers. CT images of a marijuana smoker show paraseptal emphysema in the bilateral upper lobes. CT images in a tobacco smoker with centrilobular emphysema. (Courtesy of Radiology)
"The mean number of years of marijuana use was lower than that of cigarette smokers and combined marijuana and cigarette smokers," Dr. Kang said. "However, smoked marijuana is often unfiltered, which can potentially lead to more harmful particles entering the airways and lungs."
Combined marijuana and cigarette smokers were three to four times more likely to have thickening of the airway walls, which can lead to infections, scarring, and further damage to the airways. The association with marijuana only and smoking only with bronchial wall thickening was not as significant. Similar results were observed with centrilobular and paraseptal emphysema, suggesting that the combination of cigarette smoking and marijuana may have a synergistic role in the lungs and airways.
"With our study, we showed that smoking marijuana has physical effects on the lungs and that smoking cigarettes and smoking marijuana can have a combined harmful effect on the lungs," Dr. Kang said.
According to Dr. Kang, more research is needed to identify the long-term effects of smoking marijuana. "There is a common misconception among the public that smoking marijuana is not harmful," Dr. Kang said. "More research needs to be done in this area, so the public can make an informed decision about their recreational use of marijuana."
Co-authors are Sebastian Karpinski, B.Sc., Paul Sthiadoss, MBBS, Eric Lam, M.Sc., Eric Hutfluss, MD, O. Osorio, MD, DA Hashem, MD, Matthew DF McInnes, MD, and Giselle Y. Revah , M.D.
