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The Study Claiming That Cannabis Could Be an Adjunct Treatment for Covid-19 Faces Some Criticism

Published: May 29, 2020   
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In light of the seriousness of the Covid-19 pandemic, there is an urgent need to identify and develop new therapies and strategies that may help to halt the spread of the virus and lessen the impact on those affected.

Given the anti-inflammatory effects of cannabis and its ability to alter immune systems, many have considered whether the drug could hold some therapeutic benefit to the coronavirus disease. Thus, several trials are now taking place around the world which seek to test this idea.  

In recent weeks, the early results of one of these studies have surfaced in popular outlets, such as the New York Post and Merry Jane. But have the facts been sensationalized?

What has the study found?

The findings at the center of both of these widely shared news articles are from a new study led by researchers at the University of Lethbridge, Canada, which is investigating the effects of cannabis extracts on infection.

Similarly to other respiratory pathogens, the SARS-CoV2 coronavirus is transmitted through respiratory droplets and enters into the body using receptor-mediated entry involving the angiotensin-converting enzyme II (ACE2), which is present in lung tissue and in the oral and nasal mucosa, the researchers write. It would then follow that modulation of ACE2 levels in these tissues could be a plausible way of reducing susceptibility to these types of diseases.

The University of Lethbridge study looked at 22 strains of cannabis developed by the researchers and studied the effect that these extracts had on ACE2 gene expression and ACE2 protein levels in artificial human tissue models.

They found 13 high-CBD strains that appeared to modulate ACE2 expression in these tissues, and also observed some extracts to suppress levels of serine protease TMPRSS2, another protein thought to be key in allowing these viruses entry to the body.

“While our most effective extracts require further large-scale validation, our study is crucial for the future analysis of the effects of medical cannabis on Covid-19,” the researchers wrote. “The extracts of our most successful and novel high CBD C. sativa lines, pending further investigation, may become a useful and safe addition to the treatment of Covid-19 as an adjunct therapy.”

The Merry Jane article reported the results of this study under the headline “Cannabis May Stop Coronavirus From Infecting People, Study Finds.” This article was widely shared on Facebook, but notably, the post was flagged as potentially containing misleading information by Facebook; as the researchers themselves note in their published findings, the study results do still require large-scale validation.

Speaking to PolitiFact about the seemly exaggerated headline, lead researcher Igor Kovalchuk confirmed that, “Yes, this is an overstatement.”

Study design and a lack of peer-review

Overstated reports of these cannabis and Covid-19 study findings can make it difficult to know the current scientific understanding of these issues. But it’s also important to actively read the studies themselves with a critical eye.

In a Twitter thread, Leafly’s director of science and innovation, Nick Jikomes, PhD, broke down the findings of the new Canadian study, in which he highlighted several flaws.

Firstly, Jikomes pointed out that this study was published in Preprints, and has not yet been subject to peer review. Also, research teams may feel pressured to rush and publish their Covid-19 related study results as quickly as possible, which more generally could lead to lower quality research.

A figure from the paper shows the effects of the cannabis extracts on ACE2 transcript levels in the tissue, with two extracts marked with an asterisk indicating statistical significance. In the caption of this figure, it’s revealed that the data represented by the bars in the bar chart is an average of just two samples per extract. In the words of Jikomes, This is... not compelling.”

One graph in the paper, titled figure B, is supposed to represent a “larger scale follow up experiment,” and yet the researchers don’t attempt to replicate their statistically significant results from figure A, nor do any of these other extracts meet their threshold for statistical significance. Yet still, the researchers conclude that three of the extracts included in figure B (#9, #45, and #167) are able to down-regulate ACE2 transcript levels.

In the paper, the researchers write that “levels of ACE2 protein... were significantly (p<0.05) down-regulated by extracts #7, #9, #157, #167 and #169,” despite this conclusion not matching up with the visually presented data in figure C – here #9 is not indicated as a statistically significant result.

Additional inaccuracies were noted by other scientific experts responding to the Twitter thread.

“Honestly, after I read it through, I was less than convinced,” replied Alex Chisholm, a PhD candidate in neurobiology and cannabis science communicator. “There are no effect sizes listed anywhere, wasnt convinced by the stats explanation, no explanation of why only some ‘strains’ ‘work,’ also would have expected some CBD or THC only controls.”

“Also if you missed it #81 which produces ‘statistically significant effect’ for oral tissues, doesnt show the same effect for Airway tissues... if anything its higher....dont know how they are gonna reconcile that,” she added.

Too soon to consider cannabis as a coronavirus cure

Jikomes concluded his thread by noting that in the competing interests section of the paper, the researchers acknowledge that they are funded by Pathway Research and Swysh – two startup companies in the cannabis space. He believes that, presumably, these firms will soon start to develop cannabis extract-based products intended for use as some sort of preventative for contracting viruses.

As research into cannabis and its effect (or lack thereof) on viral infection continues, more study papers will be published on the topic. It’s important to read these through a critical lens and understand that these trials are still at a very early stage. It’s too soon to conclude that cannabis could prove effective against Covid-19, and far too soon to trust any products which make claims to do so.


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