No, marijuana is no more harmful than tobacco

Another questionable study is being used to fuel Reefer Madness 2.0. Here’s what this 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 Harm Smokers More Than Cigarettes Alone,” which attempts to address concerns that smoking cannabis may be more harmful than smoking cigarettes.

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

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


Study surveys 80,000 cannabis users when, how and why they use the plant

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

In fact, no pure marijuana smokers have been studied

(Adobe Stock)

Rule number one of newly published studies: read the results for yourself. If the information source is not clearly linked, you should be skeptical of any conclusions drawn about new research until you have verified it yourself.

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

It is included in the article title itself. The CT findings in the study were not from marijuana smokers. They came from tobacco smokers who also smoked cannabis. No pure cannabis smokers were included in the study.

How the study was set up


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 examine the effects of marijuana smoking on the lungs. We wanted to determine if there were any identifiable sequelae on chest CT scans, including emphysema and signs of airway inflammation.”

To form test groups, the researchers reviewed the medical records of patients seen between 2005 and 2020. The study states: “A chest CT scan was identified in 33 pure tobacco smokers between April and June 2019.”


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“If marijuana use was detected, the patient was excluded from the pure tobacco users group, “added to the marijuana smokers group, and a new patient selected.”

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

Probably not a good idea to smoke cigarettes and marijuana

Marlboro(Olivia de Salve Villedieu/Wikimedia Commons)

So the study didn’t actually find that “marijuana may harm smokers any more than cigarettes alone,” as the Wall Street Journal headline claimed. But that’s the takeaway that’s going to be circling the media world and, in fact, has been picked up by numerous other news outlets, including CNN and USA Today.

In some really useful news, the study authors noted that smoking both tobacco and cannabis is not healthy. “The study authors found bronchial thickening in 64% of marijuana smokers versus 42% of tobacco smokers and a condition that resulted in excessive mucus production in 23% of marijuana smokers versus 6% of tobacco smokers,” The Street reported. I agree.

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

What have previous studies revealed?


A 2007 study found an association between emphysema and other lung problems in cannabis smokers compared to non-smokers, but tobacco or cigarettes were not part of the research.

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

The UAB study found, “With marijuana exposure levels that are common among Americans, occasional marijuana use was associated with increases in pulmonary airflow rates and an increase in lung capacity,” the study’s lead researcher said. “These increases were not large, but they were statistically significant. And the data showed that even up to a moderately high level of use – one joint per day for seven years – there is no evidence of reduced airflow rates or lung volumes.”


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This study acknowledged that lifetime smoke exposure can still be harmful, but that long-time, heavy cannabis users are not easy to find for study given the plant’s sticky legal status.

Funded by the National Heart, Lung and Blood Institute, the UAB Study is a long-term research project involving more than 5,000 black and white men and women from Birmingham, Chicago, Minneapolis and Oakland to study the development and determinants of cardiac Investigate vascular disease disease and its risk factors. Participants were recruited between the ages of 18 and 30 and followed them from 1985 to 2006.

Look at the source

In the age of misinformation, even verified, ticked sources can peddle fake news. This is why it is so important to verify the validity of messages before believing them or sharing them with others.

As for the bogus headlines using the tobacco and marijuana study to lure clicks and fuel Reefer Madness 2.0, shut that noise at the door. When your relatives start citing that fake headline at Thanksgiving dinner this year, arrive armed with facts.

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