Cannabis could be more harmful to the lungs than tobacco, study suggests

The small-scale study evaluated and compared chest CT scans of cannabis smokers, tobacco smokers, and nonsmokers.
Mert Erdemir
Marijuana cannabis joint stock image.
Marijuana cannabis joint stock image.


A recent study conducted by researchers from the University of Ottawa and the Ottawa Hospital suggests that smoking cannabis could be more harmful to the lungs and the respiratory tract than tobacco.

In the small-scale study, researchers evaluated chest X-ray scans of 56 cannabis smokers, 33 tobacco-only smokers, and 57 nonsmokers as control patients between October 2005 to July 2020. They compared the rates of emphysema, airway changes, gynecomastia, and coronary artery calcification between the groups.

The results revealed that regular cannabis smokers had higher rates of airway inflammation, emphysema, which is a chronic lung condition, and gynecomastia compared to regular tobacco smokers and nonsmokers.

The way you consume substances could boost the negative effects

"Marijuana smoking is on the rise, and there's a public perception that marijuana is safe, or that it's safer than (tobacco) cigarettes," Giselle Revah, a radiologist at the Ottawa Hospital, told AFP, according to a report by ScienceAlert. "But this study raises concerns that this may not be true."

Reval further added that the reason why cannabis smokers have higher rates of inflammation and disease than tobacco smokers could be related to the ways of consumption.

"Marijuana is smoked unfiltered, versus tobacco which is usually filtered. When you're smoking unfiltered marijuana, more particulates are reaching your airways, getting deposited there and irritating your airways," she said.

"People usually take bigger puffs and hold the smoke in their lungs longer for marijuana, which may lead to more trauma to those air spaces."

More research is needed

As a limitation of the study, researchers stated that some of the cannabis smokers also smoked tobacco, so some of the lung scans may have produced inconclusive results. Therefore, more study on the topic is necessary to acquire more reliable results.

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At the end of the study, marijuana smokers showed distinct radiologic findings in the lung, including higher rates of paraseptal emphysema and airway inflammatory changes, such as bronchiectasis, bronchial wall thickening, and mucoid impaction, when compared to nonsmokers and those who only smoke tobacco.

The study paper concludes that more and larger-scale studies should be conducted to comprehend the effects of marijuana use, especially considering that more and more countries are legalizing its use for medical and recreational purposes.

The research paper was published in the journal Radiology.


Background: Global consumption of marijuana is increasing, but there is a paucity of evidence concerning associated lung imaging findings.

Purpose: To use chest CT to investigate the effects of marijuana smoking in the lung.

Materials and Methods: This retrospective case-control study evaluated results of chest CT examinations (from October 2005 to July 2020) in marijuana smokers, nonsmoker control patients, and tobacco-only smokers. We compared rates of emphysema, airway changes, gynecomastia, and coronary artery calcification. Age- and sex-matched subgroups were created for comparison with tobacco-only smokers older than 50 years. Results were analyzed using χ2 tests.

Results: A total of 56 marijuana smokers (34 male; mean age, 49 years ± 14 [SD]), 57 nonsmoker control patients (32 male; mean age, 49 years ± 14), and 33 tobacco-only smokers (18 male; mean age, 60 years ± 6) were evaluated. Higher rates of emphysema were seen among marijuana smokers (42 of 56 [75%]) than nonsmokers (three of 57 [5%]) (P < .001) but not tobacco-only smokers (22 of 33 [67%]) (P = .40). Rates of bronchial thickening, bronchiectasis, and mucoid impaction were higher among marijuana smokers compared with the other groups (P < .001 to P = .04). Gynecomastia was more common in marijuana smokers (13 of 34 [38%]) than in control patients (five of 32 [16%]) (P = .039) and tobacco-only smokers (two of 18 [11%]) (P = .040). In age-matched subgroup analysis of 30 marijuana smokers (23 male), 29 nonsmoker control patients (17 male), and 33 tobacco-only smokers (18 male), rates of bronchial thickening, bronchiectasis, and mucoid impaction were again higher in the marijuana smokers than in the tobacco-only smokers (P < .001 to P = .006). Emphysema rates were higher in age-matched marijuana smokers (28 of 30 [93%]) than in tobacco-only smokers (22 of 33 [67%]) (P = .009). There was no difference in rate of coronary artery calcification between age-matched marijuana smokers (21 of 30 [70%]) and tobacco-only smokers (28 of 33 [85%]) (P = .16).