Emphysema is more common in marijuana smokers than cigarette smokers
Airway inflammation and emphysema are more common in marijuana smokers than cigarette smokers, according to new research. Researchers said the difference may be due to the way marijuana is smoked and the fact that marijuana smoke enters the lungs unfiltered. The research was published Nov. 15 in Radiologya journal of the Radiological Society of North America (RSNA).
Marijuana is the second most smoked substance after tobacco and one of the most widely used psychoactive substances in the world. Amid the legalization of recreational marijuana in Canada and many states in the US, its use has increased significantly in recent years. With its growing use, there is an urgent need for information on the effects of marijuana on the lungs, something that is currently lacking.
“It has been suggested that smoking a marijuana joint deposits four times more particles in the lungs than an average tobacco cigarette.” — Giselle Revah, MD
“We know what cigarettes do to the lungs,” said study author Giselle Revah, MD, a cardiothoracic radiologist and assistant professor at the University of Ottawa in Ottawa, Canada. “There are well-researched and well-established findings of cigarette smoking on the lungs. We know very little about marijuana.”
To find out more, Dr. Revah and colleagues compared chest CT results of 56 marijuana smokers with those of 57 nonsmoking controls and 33 tobacco-only smokers.
Three-quarters of marijuana smokers had emphysema, a lung disease that causes breathing difficulties, compared to 67% of smokers who smoked only tobacco. Only 5% of non-smokers had emphysema. Paraseptal emphysema, which damages the small ducts that connect to the air sacs in the lungs, was the predominant emphysema subtype in marijuana smokers compared to the tobacco-only group.
Airway inflammation was also more common in marijuana smokers than in nonsmokers and smokers who smoked only tobacco. The same was true of gynecomastia, a condition of enlarged male breast tissue due to a hormonal imbalance. Gynecomastia was found in 38% of marijuana smokers, compared to only 11% of tobacco-only smokers and 16% of controls.
The researchers found similar results among age-matched subgroups, where rates of emphysema and airway inflammation were again higher in the marijuana smokers than in the smokers who only smoked tobacco.
There was no difference in coronary artery calcification between age-matched marijuana groups and tobacco-only groups.
According to dr. Revah, the results were surprising, especially when you consider that the patients in the tobacco-only group had an extensive smoking history.
“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 over tobacco,” she said. “Moreover, our results were still significant when we compared the non-age matched groups, including younger patients who smoked marijuana, who were thought to have less lifetime exposure to cigarette smoke.”
According to the CDC, 48.2 million people, or about 18% of Americans, used marijuana at least once in 2019.
There are likely several factors that contribute to the differences between the two groups. Marijuana is smoked unfiltered, Dr. Revah, while tobacco cigarettes are usually filtered. This results in more particles reaching the airways from smoking marijuana.
In addition, marijuana is inhaled with a longer breath hold and a longer puff volume than tobacco smoke.
“It has been suggested that smoking a marijuana joint deposits four times more particles in the lungs than an average tobacco cigarette,” said Dr. Revah. “These particles are likely respiratory irritants.”
The higher incidence of emphysema may also be due to the way marijuana is smoked. Full inspiration with a sustained Valsalva maneuver, an attempt to exhale against an occluded airway, can lead to trauma and changes in peripheral air space.
More research is needed, Dr. Revah said, with larger groups of people and more data on how much and how often people smoke. Future research could also look at the impact of different inhalation techniques, such as through a bong, a joint or a pipe.
“It would be interesting to see if the inhalation method makes a difference,” said Dr. Revah.
For more information on this study, see Emphysema more common in marijuana smokers than in cigarette smokers.
Reference: “Chest CT Results in Marijuana Smokers” By Luke Murtha, Paul Sathiadoss, Jean-Paul Salameh, Matthew DF Mcinnes, and Giselle Revah, November 15, 2022, Radiology.