Smoking marijuana may be more harmful to smoker’s lungs than tobacco, new study finds

But more research is needed on the overall health effects of marijuana.

Cannabis may do more harm to a smoker’s lungs and airways than tobacco, according to a small Canadian study published Tuesday.

Researchers from the University of Ottawa and The Ottawa Hospital looked at chest X-ray scans of 56 cannabis smokers, 57 non-smokers and 33 people who smoked only tobacco between 2005 and 2020.

They found higher rates of airway inflammation and emphysema – a chronic lung disease – among regular cannabis smokers compared to regular tobacco-only smokers and non-smokers.

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Challenging perception

“Marijuana smoking is on the rise and there’s a public perception that marijuana is safe, or that it’s safer than (tobacco) cigarettes,” Giselle Revah, a radiologist The Ottawa Hospital, where the research was conducted, told AFP.

“But this study raises concerns that this may not be true.”

Smoking marijuana may be more harmful to smoker's lung than tobacco, new study finds
Airway changes in a 66-year-old male marijuana and tobacco smoker. Contrast-enhanced (A) axial and (B) coronal CT images show cylindrical bronchiectasis and bronchial wall thickening (arrowheads) in multiple lung lobes bilaterally in a background of paraseptal (arrows) and centrilobular emphysema. Image credit: Radiological Society of North America

She said the higher rates of inflammation and disease among cannabis smokers versus tobacco could be related to the differences in how the drugs are typically consumed.

“Marijuana is smoked unfiltered, versus tobacco which is usually filtered,” she said.

“When you’re smoking unfiltered marijuana, more particulates are reaching your airways, getting deposited there and irritating your airways.”

Also, she added, “people usually take bigger puffs and hold the smoke in their lungs longer for marijuana, which may lead to more trauma to those air spaces.”

Smoking marijuana may be more harmful to smoker's lung than tobacco, new study finds
Pulmonary emphysema in (A, B) marijuana and (C, D) tobacco smokers. (A) Axial and (B) coronal CT images in a 44-year-old male marijuana smoker show paraseptal emphysema (arrowheads) in bilateral upper lobes. (C) Axial and (D) coronal CT images in a 66-year-old female tobacco smoker with centrilobular emphysema represented by areas of centrilobular lucency (arrowheads). Image credit: Radiological Society of North America

More research needed

Despite these possible explanations, the authors of the study, which was published in the journal Radiology, pointed out that some of the cannabis smokers also smoked tobacco, and that some of the lung scans produced inconclusive results, meaning more study is necessary.

As Revah noted, there is very little research on the health effects of cannabis overall, as it is banned in most countries.

Canada, where the researchers are based, legalized recreational use of cannabis in 2018. 

It is also legal for recreational use in Uruguay and Mexico, among other countries, and many US states, while several other countries and territories have also recently decriminalised possession of the drug or approved it for medicinal use. 

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