Study Shows Marijuana Smokers at Higher Risk than Tobacco Users


A man smoking marijuana – Photo credit: Mel Evans

Regular marijuana smokers appear to be more at risk of lung damage than those who smoke tobacco, a recent study has found.

The research which was conducted by a group of scientists at the University of Ottawa in Ontario , published in the RSNA Journal, discovered that marijuana smokers showed higher rates of airway inflammation and may develop lung damage earlier or with less exposure.

“There's a public perception that marijuana is safe, this study is raising concern that this might not be true,” says Giselle Revah, MD, a radiologist at the University of Ottawa in Ontario.

She and her colleagues compared the chest CT scans of 57 non-smokers and 33 tobacco users to those of 56 marijuana smokers.

According to Revah, she can often determine right away if a CT scan belongs to a heavy or long-term cigarette smoker. She started to worry, however, what smoking marijuana does to the lungs and whether she would be able to distinguish its effects from those of smoking cigarettes when its usage became more widespread and legalized in Canada and many other nations.

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Emphysema rates were still marginally higher among marijuana users without age matching (75% vs. 67%) despite the fact that the difference was no longer statistically significant. However, according to Revah, all of the marijuana users were 50 years of age or older, whereas more than 40 per cent of the tobacco users were under 50.

She claims that the findings corroborate what her family medicine colleagues have observed in practice.

“In their practices, they have younger patients with emphysema,” she says.

The findings are “not even a little bit surprising,” says Alan Kaplan, MD, a family doctor in Ontario who has expertise in respiratory health.

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Lung specialists remarked in the editorial that the new data provides context for a recent rise in referrals for a collapsed lung. According to the authors, they only got six of these recommendations between 2012 and 2020 but received 22 of them within the last two years.

“Many, but not all, of these patients have a documented history of marijuana use,” they write.

According to Kaplan, the method marijuana is smoked might be one factor contributing to the increased harm. Marijuana users might harm their lungs because they “take a large breath in, and they really force it into lungs and hold pressure on it”.

It is hard to tell whether the observed harm was brought on by marijuana alone or by marijuana combined with tobacco because the majority of research participants who used marijuana also smoked cigarettes, according to Revah.

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The marijuana group was compared to tobacco users who had a long history of smoking – 25 to 100-years – and who were from a high-risk lung cancer screening program, she claims, and the results are still startling.

Revah and her associates are currently working on a bigger investigation to determine whether they can corroborate their findings.

“The message to physicians is to ask about cannabis smoking. In the past, people have been reluctant to admit using cannabis. Even with legalization, they may be slow to tell their physicians. But clinicians should still try to identify frequent users, especially those who are predisposed for lung conditions. If they intend to use the drug, the advice should be, there are safer ways to use cannabis,” he said.


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