A new study suggests marijuana smoking may be more damaging to the lungs than cigarette smoking. Research published Tuesday in Radiology, a journal of the Radiological Society of North America, found that emphysema (a lung condition that causes shortness of breath) and airway inflammation are more common in marijuana smokers compared with cigarette smokers. The study supports previous evidence in animals and humans indicating that marijuana use is linked to an increased likelihood of developing emphysema, but contradicts other research showing that marijuana is less harmful to the lungs than tobacco. “The results are unexpected and a replication study seems warranted — tobacco smokers consume many more cigarettes a day than cannabis smokers, so we would expect higher rates of irritation in the respiratory system as a result,” said Keith Humphreys, PhD, a professor of psychiatry and behavioral sciences at Stanford University, whose research covers addiction to tobacco and marijuana. “But at the same time, we still don’t understand all the components of the cannabis plant and it may have some unique ability to do damage to the airways that has not been studied,” added Dr. Humphreys, who was not involved in the investigation. Led by researchers at the University of Ottawa in Canada, the study compared chest computerized tomography (CT) scans from 56 marijuana smokers with those of 57 nonsmoking controls and 33 tobacco-only smokers. These X-ray images revealed that three-quarters of the marijuana smokers had emphysema compared with 67 percent of the tobacco-only smokers. Nonsmokers fared much better, with just 5 percent of them showed signs of emphysema. Scientists noted that paraseptal emphysema, which impairs the tiny ducts that connect to the air sacs in the lungs, was the predominant emphysema subtype in marijuana smokers compared with the tobacco-only group. CT scans also showed airway inflammation to be more frequent among marijuana smokers than nonsmokers and tobacco-only smokers. In addition, gynecomastia (an increase in the amount of breast gland tissue in boys or men, caused by an imbalance of the hormones estrogen and testosterone, per Mayo Clinic) was found in 38 percent of the marijuana smokers compared with 11 percent of the tobacco-only smokers and 16 percent of the controls. Lead study author Giselle Revah, MD, a cardiothoracic radiologist and assistant professor at the University of Ottawa, described the results as surprising, considering 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 above tobacco,” said Dr. Revah in a statement. The evidence points to marijuana and tobacco use having a combined effect on the lungs that may be greater than the effect either drug has individually. Revah and her colleagues highlighted that risks for emphysema and airway inflammation were similar no matter the age of the participants. While the study did not determine the reasons behind the result differences between marijuana and cigarette smokers, the authors suggested some factors. Because marijuana is often smoked unfiltered and tobacco is often smoked filtered, more particulates may be entering the lungs of marijuana users. Also, marijuana is inhaled with a longer hold of breath and volume of smoke compared with cigarettes. “It has been suggested that smoking a marijuana joint deposits four times more particulates in the lung than an average tobacco cigarette,” said Revah in a press release. “These particulates are likely airway irritants.” More study is needed involving larger groups of people and more data on how much and how often people are smoking, according to the research team. They said a look at the impact of different inhalation techniques — such as through a bong, a joint, or a pipe — may be revealing. “Marijuana has been marketed as harmless, indeed even as a cure for many diseases,” said Humphreys. “But the truth is that the drug itself, as well as the act of smoking anything, can damage your body.”
