Marijuana is the most widely smoked substance in the world, second only to tobacco. And its use is on the increase since it has become legalized for recreational purposes in some of the U.S. states, as well as in Canada (in 2018). However, not very much is known about the effects that marijuana has on the lungs, and images of lung condition in long-term marijuana users are not readily available.
A recent study, comparing the chest CT images from 56 marijuana smokers with those of 57 non-smoking controls and 33 individuals who smoked only tobacco, has now been published in Radiology, a journal of the Radiological Society of North America. The CT images were taken between 2005 and 2020, and show that those who smoke marijuana are more likely to suffer from emphysema, a lung disease that makes it difficult to breathe in enough oxygen.
Dr. Giselle Revah, a cardiothoracic radiologist and assistant professor in the Faculty of Medicine at the University of Ottawa, in Ottawa, Canada, was first author on the study. She was searching for information on the effect of marijuana on the lungs, and its health implications.
“I can tell if someone is a heavy or a long-time cigarette smoker when I look at a CT scan. With marijuana being the second most inhaled substance after tobacco, I started wondering: What does marijuana inhalation look like on a CT scan? Would I be able to tell if someone was a marijuana smoker; is it different from cigarette smoke?” says Dr. Revah.
“What’s unique about this study, is that there hasn’t been anything comparing the imaging findings in tobacco smokers to marijuana smokers before. In fact, there is a lack of imaging research in marijuana, probably because it’s still illegal in many parts of the world, and in many U.S. states, which is why I think we were the first to do a project like this.”
The comparison showed that 75 percent of the marijuana smokers had emphysema, compared with 67 percent of those who smoked tobacco only. To put this in perspective, only 5 percent of the non-smokers had emphysema. Paraseptal emphysema, which damages the tiny ducts that connect to the air sacs in the lungs, was the predominant type of emphysema seen in marijuana smokers compared to the tobacco-only group.
In addition, the researchers found evidence suggesting that marijuana smokers suffered other health effects on their lungs, including more instances of large and small airway diseases. Airway inflammation was more common in marijuana smokers than non-smokers and tobacco-only smokers, as was gynecomastia, the condition of enlarged male breast tissue due to hormone imbalance. Gynecomastia was found in 38 percent of the marijuana smokers, 11 percent of the tobacco-only smokers and 16 percent of non-smoking controls.
Dr. Revah said the overall results were surprising, especially considering that the patients in the tobacco-only group had extensive histories of smoking.
“The fact that our marijuana smokers – some of whom also smoked tobacco – had additional findings of airway inflammation/chronic bronchitis suggests that marijuana has additional synergistic effects on the lungs above tobacco,” she said. “In addition, our results were still significant when we compared the non-age-matched groups, including younger patients who smoked marijuana and who presumably had less lifetime exposure to cigarette smoke.”
The differences between the effects of marijuana and tobacco smoke may be due to the specific ways in which the substances are smoked. Marijuana is smoked unfiltered; and this results in more particulates reaching the airways. In addition, marijuana is inhaled with a longer breath hold and puff volume than tobacco smoke.
“It has been suggested that smoking a marijuana joint deposits four times more particulates in the lung than an average tobacco cigarette,” Dr. Revah said. “These particulates are likely airway irritants.”
While smoking marijuana, a full inhalation with a sustained Valsalva maneuver, an attempt at exhalation against a closed airway, may also lead to trauma and peripheral airspace changes. Dr. Revah recognizes that more data is needed, particularly involving how much and for how long marijuana has been used. She also states it would be interesting to find out if the technique of smoking, such as through a bong, a joint or a pipe, has an influence on the damage caused.
“We’ve identified an association between marijuana smoking and damage to both the small and the large airways,” she said. “We still need more research before we can effect policy change. We need larger, more robust prospective studies with more patients to confirm it.”
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