Ingredient in common over-the-counter cough medicines helps coronavirus grow, says research

Ingredient in common over-the-counter cough medicines helps coronavirus grow, says research
(Getty Images)

A common ingredient found in over-the-counter cough medicines appears to have the potential to promote the growth of the new coronavirus, researchers have found in a laboratory experiment.

An international team of more than 120 scientists analyzed the impact of over-the-counter and prescription drugs on Covid-19. They found that the presence of an ingredient commonly found in cough suppressants, called dextromethorphan, helps the virus. Dextromethorphan promoted SARS-CoV-2 (the virus that causes Covid-19) infection in the laboratory experiment. When the research team tested infected cells with this compound, the virus was able to replicate more easily, and more cells died. 


The team was led by Dr Nevan Krogan, director of the Quantitative Biosciences Institute at the University of California, San Francisco, and a senior investigator at Gladstone Institutes. Based on their findings, the researchers have urged that this compound be used wisely during the Covid-19 pandemic. 

If a person has Covid-19, they may have mild (or no symptoms) to severe illness. The symptoms can include fever, cough, shortness of breath, among others. Accordingly, given that cough suppressants may be used by people with coronavirus, whether they have been officially diagnosed or not, the researchers have called for more research on dextromethorphan’s safety.

According to the researchers, while the findings from their study is potentially very important, they emphasize that more tests are needed to determine if cough syrup with this ingredient should be avoided by someone who has Covid-19.

“We find that the widely used antitussive dextromethorphan harbors proviral activity and therefore, its use should merit caution and further study in the context of Covid-19,” say researchers in their findings published in Nature. 

Brian Shoichet from the University of California, San Francisco School of Pharmacy, who was involved in the study, said during a briefing, “We’re not necessarily recommending that everyone stop taking dextromethorphan.” “But because the lab results demonstrate a pro-viral effect, it would be wrong not to highlight it, because it could be detrimental,” added Shoichet.


Dextromethorphan is used to temporarily relieve cough caused by the common cold, the flu, or other conditions. Dextromethorphan is in a class of medications called antitussives. It works by decreasing activity in the part of the brain that causes coughing. It is used in cough syrup, tablets, capsules and lozenges. 


Dextromethorphan is used to temporarily relieve cough caused by the common cold, the flu, or other conditions. It is used in cough syrup, tablets, capsules and lozenges (Getty Images)

Study also shows some promising results

Rather than focusing on an antiviral approach to block SARS-CoV-2, the researchers first combined biological and computational techniques to create a ‘blueprint’ of more than 300 human proteins that the virus requires to infect human cells and to thrive and replicate in the body. They then explored the question of which drugs, both those that are currently marketed as well as those in development, might be repurposed to treat SARS-CoV-2 infection by targeting those human proteins.

Since it is not known yet which human cells work best for studying the coronavirus in the laboratory, the experts used African green monkey cells. They are frequently used in place of human cells to test antiviral drugs. “They can be readily infected with the coronavirus and respond to drugs very closely to the way human cells do,” Dr Krogan writes in The Conversation.

The researchers introduced the coronavirus proteins into cells in culture. Once inside the cells, the viral proteins found specific human proteins that they could latch onto, very much as they would during a normal infection. After identifying these proteins and determining small molecules known to bind them based on prior scientific research, the scientists identified 69 molecules that seemed most promising based on their “targeting specificity.” 

Subsequently, the team evaluated the impact of 47 of these compounds in cells infected with live virus, as well as an additional 28 compounds known to act on two key targets identified by other methods. These experiments were required to quickly establish robust and quantitative “viral replication inhibition assays under high biocontainment to study the impact of these compounds on the biological cycle” of the novel coronavirus. 

“Our multidisciplinary team of researchers identified 69 existing drugs and compounds with potential to treat Covid-19. We have tested 47 of these drugs and compounds in the lab against live coronavirus. I’m happy to report we’ve identified some strong treatment leads and identified two separate mechanisms for how these drugs affect SARS-CoV-2 infection,” says Dr Krogan.


The researchers emphasize that while the drugs identified in the study are promising, they have only been tested against the virus in laboratory experiments. The team does not advocate anyone prescribing and/or using the drugs unless human clinical trials find them to be safe and effective.

The next step is to further investigate the most promising compounds to advance them as quickly as possible through clinical trials, says the team. “We are working with several pharma and biotech companies to evaluate the antiviral effectiveness and safety of drug candidates that showed the most promise in our laboratory experiments,” says Dr Krogan.


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