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No, marijuana is not more harmful than tobacco

Another questionable study is being used to stoke Reefer Madness 2.0. Here’s what that study really found, and why it’s being used to mislead the public.


Earlier this week the Wall Street Journal published a health article titled “Marijuana May Hurt Smokers More Than Cigarettes Alone,” attempting to raise concerns that smoking cannabis may be more harmful than smoking cigarettes.

The article was based on a new study from Canada, which compared the lung health of cigarette smokers, and cigarette smokers who also smoke cannabis. But many outlets are spinning the data before washing it in context for readers.

That Wall Street Journal headline? It’s just wrong.

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Here’s what that study really found, plus answers as to why cannabis users are being bombarded with misleading info about the plant from seemingly reputable sources.

No marijuana-only smokers were actually studied

(Adobe Stock)

Rule number one about newly-released studies: Read the findings yourself. Unless the source of information is clearly linked, be skeptical of whatever conclusions are made about new research until you review it yourself.

In this case, a simple look at the study in question—“Chest CT Findings in Marijuana Smokers,” published on Nov. 15 in the journal Radiology—reveals a major issue.

It’s contained in the article title itself. The CT findings in the study weren’t from marijuana smokers. They were from tobacco smokers who also smoked cannabis. No cannabis-only smokers were included in the study.

How the study was set up

(AdobeStock)

The study’s lead author, a diagnostic radiologist at Ottawa Hospital in Ontario, Canada, wrote: “The purpose of this study was to use chest CT to investigate the effects of marijuana smoking on the lung. We sought to determine if there were identifiable sequelae on chest CT images, including emphysema and signs of airway inflammation.”

To create test groups, researchers reviewed the medical charts of patients seen between 2005 and 2020. The study states: “Thirty-three tobacco-only smokers were identified with chest CT performed between April and June 2019.”

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“If marijuana use was identified, the patient was excluded” from the tobacco-only group, “added to the group of marijuana smokers, and a new patient was selected.”

In other words, the study didn’t compare tobacco smokers to marijuana smokers. Instead, the researchers compared tobacco-only smokers to tobacco smokers who also smoked marijuana. (And a third group of patients who did not smoke anything at all.) There was no group of patients who smoked marijuana but no tobacco.

Probably not a good idea to smoke cigarettes and marijuana

Marlboro
(Olivia de Salve Villedieu/Wikimedia)

So the study, in fact, did not find that “Marijuana May Hurt Smokers More Than Cigarettes Alone,” as the Wall Street Journal headline claimed. But that’s the takeaway that will circle the media globe, and in fact has already been picked up by numerous other news outlets, including CNN and USA Today.

In actually useful news, the study’s authors found that it’s not a healthy thing to smoke both tobacco and cannabis. “The study authors found bronchial thickening in 64% of marijuana smokers versus 42% of tobacco-only smokers and a condition that leads to excess mucus buildup in 23% of marijuana smokers versus 6% of tobacco-only smokers,” reported The Street, accurately.

It’s not clear if that applies more to those who smoke cigarettes and cannabis separately, or those who mix tobacco with their cannabis.

What have previous studies found?

(ilbusca/iStock)

A study from 2007 found a connection between emphysema and other lung issues in cannabis smokers versus non-smokers, but tobacco or cigarettes were not part of the research.

A separate 2012 study by the University of Alabama at Birmingham, found “Marijuana smoke (is) not as damaging to lungs as cigarette smoke,” with a far larger sample size and more rigorous methodology to boot.

The UAB study found: “At levels of marijuana exposure commonly seen in Americans, occasional marijuana use was associated with increases in lung air flow rates and increases in lung capacity,” the study’s lead researcher said. Still, “those increases were not large, but they were statistically significant,” according to the published study.

“Data showed that even up to moderately high-use levels — one joint a day for seven years — there is no evidence of decreased air-flow rates or lung volumes.”

University of Alabama at Birmingham study
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That study acknowledged that lifetime exposure to smoke can still be harmful, but also that longtime, heavy cannabis users are not easy to find for studies, given the plant’s sticky legal status.

The UAB study was funded by the National Heart, Lung and Blood Institute. It was a long-term research project involving more than 5,000 black and white men and women from Birmingham, Chicago, Minneapolis and Oakland, designed to examine the development and determinants of cardiovascular disease and its risk factors. Participants were recruited when they were ages 18-30 and followed them from 1985 to 2006.

Consider the source

In the age of misinformation, even verified, check-marked sources can be peddling fake news. That’s why it’s so important to double-check the validity of news stories before believing them or sharing them with others.

As for the phony headlines using the tobacco and marijuana study to bait clicks and stoke Reefer Madness 2.0, shut that noise down at the door with facts. When your relatives start quoting that bogus headline over Thanksgiving dinner this year, come armed with the real data, and some joints and edibles that might change their perspective on pot for good.

Calvin Stovall's Bio Image
Calvin Stovall

Calvin Stovall is Leafly's East Coast Editor.

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