There is no scientific evidence that cannabis prevents covid-19 infection

A cell culture study on cannabis and covid-19 has gone viral, giving rise to misleading headlines


The internet is currently full of articles and viral messages about a study that has supposedly shown that cannabis can help prevent covid-19 infections. But that content is MISLEADING: what has been discovered in preclinical trials is that certain chemical substances present in cannabis can block the virus from entering human cells. When trials are preclinical, it means that studies have been carried out in a lab on cells, not on human beings. Which is to say: there is still a long way to go before we can see whether the findings can be replicated in real life and, if so, in what way. 

Scientists: Cannabis can prevent covid-19 infections

Misleading headlines that ignore the details of scientific studies are a common source of misinformation. The case of cannabis and the possible reduction of covid-19 infections is one such example. 

Some media sources have pointed out in their headlines that “cannabis can prevent covid-19 infection”, but in reality what the team of scientists led by Richard van Breemen, professor in the Department of Pharmaceutical Sciences at Oregon State University, observed in the study in question by means of a technology known as affinity selection-mass spectrometry is that certain chemical compounds – cannabigerolic acid (CBGA), cannabidiolic acid (CBDA), and tetrahydrocannabinolic acid (THCA) – bind to the spike protein (Spanish only) of SARS-CoV-2, and that the former two acids can block the virus from entering the cell, which is the first step in the infection process. Originally published in the Journal of Natural Products, the study has since gone viral.

The issue is that the trial “uses cells in culture, not in vivo models”, a fact pointed out to Verificat by Manuel Guzmán (Spanish only), professor of biochemistry and molecular biology at the Complutense University of Madrid and vice president of the Spanish Agency of Medicinal Cannabis (OECDM). In other words, it falls into a category that the scientific community considers preclinical.

This sort of interpretation of a preclinical trial has already been used to validate the misconception that compounds such as povidone-iodine, used to make Betadine, are effective in the prevention of covid-19. In this particular case, which we addressed in this article (Spanish and Catalan only), povidone-iodine was shown to be very effective against coronavirus in laboratory studies, but not when consumed directly by human beings. Several people have therefore concluded that the same could happen in real life, but so far the scientific evidence does not conclude the same.

In medicine, this type of study is a first step towards testing a medication in humans. “Its main purpose is to demonstrate a lack of adverse side effects,” explains Fundación Genoma España in its guide to preclinical developments. “Only once it has reached the clinical phase (which is carried out on human beings) does it focus on testing the drug’s therapeutic efficacy”. 

In fact, Professor van Breemen himself insists that even though the study “establishes a mechanism of action by which the cannabinoid acids can prevent entry into the cell by SARS-CoV-2, which causes covid-19, it still requires clinical trials in order to establish the efficacy and to determine the optimal dose and form of administration”.

Cannabis pills

The headline stating that “cannabis can prevent covid-19 infection” has led many people to wonder whether smoking a joint could be effective at preventing the illness, but there is nothing further from the truth. The lead researcher of the study himself explained in an email that “cannabinoid acids are sensitive to heat and can decompose if smoked. Smoking is therefore probably not the ideal way to administer it”.

In addition, as Eduardo Muñoz, professor of immunology at the Maimonides Biomedical Research Institute of Cordoba (IMIBIC) and member of the Spanish Society for Cannabinoid Research (SEIC), has pointed out to Verificat, the doses used in vitro “are very high and could not be achieved in the oral use of these cannabinoids”. Guzmán concurs: “The doses of CBD that the researchers add to the cells in order to inhibit the viral infection are much higher than those that could be achieved in the body of a person using, for example, a CBD oil. “In other words”, he concludes, “the experimental system used by the authors of this paper is ‘very contrived’”. 

For all these reasons, Muñoz considers using this particular piece of news to state that certain cannabinoids can be effective in the treatment of covid to be “completely absurd and baseless”, and that “its true significance for covid-19 is minimal and anecdotal”. Guzmán believes that the trial has “little clinical value”, but “it doesn’t mean that it can’t grow in the future”.