Smoking marijuana damages the lungs more than tobacco

By Benedette Cuffari, M.Sc.Reviewed by Danielle Ellis, B.Sc.Nov 15 2022

In a recent Radiology journal study, researchers report chest computed tomography (CT) findings that the lungs of marijuana smokers exhibit more significant levels of airway inflammatory markers and emphysema as compared to those of tobacco-only smokers.

Study: Chest CT Findings in Marijuana Smokers. Image Credit: PIJITRA PHOMKHAM / Shutterstock.com

The health effects of smoking marijuana

Marijuana is the most widely used psychoactive drug throughout the world, with its global use continuing to rise following its decriminalization and/or legalization in many countries. Within Canada, for example, 20% of individuals over the age of 15 have reported having used marijuana in the past three months. Similarly, almost 13% of adults in the United States have reported marijuana use within the past year.

Although marijuana is the second most commonly smoked substance after tobacco in the world, it can be consumed in several other ways including vaporization and ingestion. As compared to tobacco smoking, marijuana smoking often involves the inhalation of greater volumes of smoke for longer periods of time. Furthermore, marijuana is frequently smoked without a filter.

Like tobacco smoke, marijuana smoke also consists of various carcinogens and chemicals capable of causing respiratory disease. In fact, several studies have confirmed that marijuana smoking can lead to respiratory symptoms like cough, sputum production, and wheezing, all of which are also commonly reported among tobacco smokers. The presence of these symptoms has been found to alter pulmonary function tests in marijuana smokers, thus indicating the likely presence of airway inflammation in these individuals.

Assessing the effects of marijuana smoke through CT imaging

In addition to pulmonary function tests, CT lung imaging can also provide important information on the impact of marijuana smoking on the lungs.

To this end, the researchers of the current study compared chest CT studies from 56 marijuana smokers, 57 nonsmokers, and 33 tobacco-only smokers obtained between October 2005 and July 2020 in Ottawa, Canada. All patients included in the current study were matched by age and sex.

Importantly, the researchers were limited in their ability to quantify daily marijuana use among the patients due to the retrospective nature of this study. In fact, only 28 of the 56 patients had provided information about their daily marijuana consumption rates, which averaged to 1.85 grams each day. Fifty of the 56 marijuana smokers also smoked tobacco.

As compared to non-smokers, the CT findings for marijuana smokers indicated different rates of emphysema, bronchial thickening, bronchiectasis, mucoid impaction, and centrilobular nodules, all of which are CT markers for airway inflammation. Gynecomastia was also reported in 38% of marijuana patients as compared to 16% of non-smokers.

Upon comparison of CT findings between marijuana and tobacco-only smokers, the researchers reported differences in bronchial thickening, bronchiectasis, and mucoid impaction. Furthermore, higher rates of emphysema were observed in age-matched marijuana smokers as compared to tobacco-only smokers of 93% and 67%, respectively. No differences were observed when comparing the occurrence of centrilobular nodules between marijuana and tobacco-only smokers; however, this may be due to the high rate of tobacco smokers who also smoked marijuana.

Paraseptal emphysema was also more frequently identified in marijuana smokers as compared to the lungs of tobacco-only smokers. Conversely, centrilobular emphysema was primarily visualized in the lungs of tobacco-only smokers.

Future outlook

In the future, larger cohort studies are needed to confirm the CT findings in this study, as well as elucidate possible pathogenic mechanisms responsible for the effects of marijuana smoke on lung damage. Furthermore, since most marijuana smokers in this study also smoked tobacco, it is difficult to ascertain whether the CT findings reported in this study were due to marijuana smoke or if they are synergistic effects of both marijuana and tobacco smoke on the lungs.