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CT Scans Reveal Higher Rates of Emphysema in Cannabis Smokers

By Alexander Beadle

Published: Apr 12, 2021   
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Cannabis smokers experience emphysema at higher rates than both non-smokers and tobacco smokers, according to new research from the Ottawa Hospital, Canada.

In the new research, due to be presented at the 2021 ARRS Virtual Annual Meeting, scientists also found cannabis smokers to be at greater risk of paraseptal emphysema (as compared to other subtypes) when compared to tobacco smokers and the control group of non-users.

Cannabis smoking associated with increased incidence of lung problems

The new study set out to understand marijuana’s effects on the lungs from a radiological perspective – a perspective largely ignored in current medical literature, according to the study’s authors.

“Given that marijuana use is increasing, particularly within nations such as Canada, that have legalized the substance, it is important for us, as radiologists, to define specific findings associated with its consumption,” wrote first author Luke Murtha, a diagnostic radiologist at Ottawa Hospital, in an accompanying presentation research summary.

The researchers from Ottawa Hospital identified three groups of age and sex-matched patients through the Ottawa Hospital Picture Archiving and Communication System (PACS): one group of cannabis smokers, a control group made up of non-smokers/non-cannabis users, and a comparison group made up of exclusively tobacco smokers. The recorded chest CT scans taken from patients were then analyzed by two board-certified, fellowship-trained radiologists who were blinded to the smoking status of each individual. 

Rates of emphysema, a lung disease that causes shortness of breath through the slow destruction of lung tissue, were significantly higher in the cannabis-using patient group; three-in-four of the scans of these patients showed signs of emphysema, compared to just 5 percent of control patients. Age-matched subgroup analysis showed a significant increase in emphysema in the cannabis-using patients (93 percent) as compared to tobacco smokers (66 percent).

The radiologists also noticed differences in the proportion of patients with paraseptal emphysema, a type of emphysema characterized by inflammation or damage to the lung’s air sacs, resulting in lifelong problems with wheezing and shortness of breath. Age-matched subgroup analysis showed a significant increase in the proportion of paraseptal emphysema, as compared to other types, in cannabis smokers (53 percent) versus tobacco-only smokers (24 percent) and the control group (7 percent).

“Marijuana smoking is also associated with airways disease, including bronchial wall thickening, bronchiectasis, and bronchiolar mucoid impaction, in comparison to both the control group and tobacco-only group,” reported Murtha.

Cannabis and respiratory issues

As demonstrated by the history of research into the health effects of tobacco, which was slow to fully comprehend the links between tobacco cigarettes and lung cancer risk, it is crucial that any potential health risks posed by the use of cannabis are identified quickly so that proper public health measures can be taken to curtail any harms. This kind of research is ongoing, with mixed findings.

A recent study from researchers at the University of Michigan School of Nursing found that teens who vape cannabis are almost twice as likely to report problems with wheezing and coughing than their peers who use tobacco cigarettes or vape nicotine products. This research, which was based on data from over 15,000 students taking part in the US national Population Assessment of Tobacco and Health (PATH) study, found that students who reported any lifetime use of cannabis vapes were at a greater risk than their peers for experiencing pulmonary irritation, including wheezing after exercise, wheezing that disrupts speech, and a night-time dry cough.

But while cannabis may produce poorer respiratory health outcomes than tobacco in this emphysema study and in the earlier pulmonary irritation study, this trend may not hold true across the board. A 2018 literature review from researchers at the Imperial College London Institute of Clinical Sciences and the Respiratory Medicine found that cannabis use may not in fact be linked to COPD, lung cancer, or other respiratory conditions that are routinely linked to tobacco use.

While cannabis may lead to some COPD-like symptoms, such as shortness of breath, the Imperial College London researchers found the evidence to be lacking for other hallmarks of COPD. Similarly, while cannabis users perform more poorly on lung function tests than non-smokers, the researchers determined that the factors contributing to these poor scores were different to the causes of poor performance in tobacco smokers. Furthermore, the literature review authors were unable to find any high-quality studies that could prove a link between cannabis use and lung cancer.

It is apparent that cannabis use can have a negative impact on pulmonary health, but why and how this happens is still unclear. Continued research, whether that be through case studies, observational studies, or radiological imaging, will all help to broaden the scientific understanding of this drug and any negative health risks it may present.


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