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Tuesday, June 06, 2023


No, Garlic will not Cure COVID.

Garlic extracts are in the news with somewhat breathless headlines ( see here [paywall] and here and here) as the Doherty Institute has reported that garlic extracts are able to prevent influenza and SARS-CoV-2 infection of cells in culture. Unfortunately, the full experimental details are not available, but the effects of garlic extracts on viral infection in isolated cells have been seen before and suggest garlic is unlikely to affect the course of COVID infection.

Garlic extract has been shown to inhibit virus activity previously (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7434784/), and SARS-CoV-2 in particular (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8581659/

 However, while these preclinical studies are an essential first step to developing therapies, there is a long way to go before these extracts can be adopted as preventatives or treatments. After all, as I said on Media Watch, many things kill viruses in dishes, including extract of old shoes.

Garlic has been used in medicines for millennia, although evidence that it is actually useful is largely lacking. Garlic’s most prominent components are organic sulfur compounds which give it its distinctive smell. More than thirty sulfur containing compounds are present in garlic along with other potentially active compounds such as lecithin's and flavonoid antioxidants (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7434784/). The organic sulfur compound Allicin is thought to be the primary component responsible for antiviral activity. 

Absorption and metabolism of the active components of garlic extracts may mean that the levels of these compounds may not reach levels that are effective in the body. In the previous In vitro studies, rather high concentrations of extract (https://journal.isv.org.ir/article-1-205-fa.pdf, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4780135/) and Allicin are required to inhibit viral activity (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8581659/). Furthermore, the cell type used in the in vitro experiments affects the results, with Allicin in human lung cells being less effective against SARS-CoV2 than Vero cells (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8581659/).

Garlic compounds are readily broken down and results suggest they do not enter the body at the levels required to inhibit viral reproduction. (https://academic.oup.com/jn/article/131/3/955S/4687054, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6073756/).
There was a suggestion that consuming garlic might help with the gastrointestinal effects of COVID, and possibly lead to faster recovery via effects on the GI tract. While it is quite clear that COVID causes gastrointestinal symptoms, it is less clear if this is due to virus in the GI tract binding to the GI epithelium, virus getting to the GI cells via the blood or due to the systemic effects of the virus. Even if it is due to virus in the GI tract infecting the GI epithelium, it is not clear there would be a high enough concentration in the gut content to stop virus binding. The major issue and really serious effects of COVID is the virus binding in the lungs (and the effects on circulation and the heart), so affecting the GI tract is not likely to have a significant impact on the course or the worst adverse effects of COVID.
Small clinical trials of garlic preparations suggest they may reduce symptoms, but not incidence, of colds and flu. The composition and concentrations of these extracts may not be comparable to the materials tested by the Doherty Institute. A small trial with a fortified garlic extract in hospitalised COVID patients showed no significant effect on the primary measures of infection recovery (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10011030/). 

Overall, while the results reported by the Doherty Institute are interesting, until clinical trials have been done no claims can be made about the effects of these extracts for the prevention and/or treatment of influenza let alone COVID. With what information we already have, an actual benefit seems highly implausible.


Rouf R, Uddin SJ, Sarker DK, Islam MT, Ali ES, Shilpi JA, Nahar L, Tiralongo E, Sarker SD. Antiviral potential of garlic (Allium sativum) and its organosulfur compounds: A systematic update of pre-clinical and clinical data. Trends Food Sci Technol. 2020 Oct;104:219-234. doi: 10.1016/j.tifs.2020.08.006. Epub 2020 Aug 19. PMID: 32836826; PMCID: PMC7434784. 

Mehrbod P., Amini E., Tavassoti-Kheiri M. Antiviral activity of garlic extract on Influenza virus. Iranian Journal of Virology. 2009;3(1):19–23. 

Chavan RD, Shinde P, Girkar K, Madage R, Chowdhary A. Assessment of Anti-Influenza Activity and Hemagglutination Inhibition of Plumbago indica and Allium sativum Extracts. Pharmacognosy Res. 2016 Apr-Jun;8(2):105-11. doi: 10.4103/0974-8490.172562. PMID: 27034600; PMCID: PMC4780135. 

Mösbauer K, Fritsch VN, Adrian L, Bernhardt J, Gruhlke MCH, Slusarenko AJ, Niemeyer D, Antelmann H. The Effect of Allicin on the Proteome of SARS-CoV-2 Infected Calu-3 Cells. Front Microbiol. 2021 Oct 28;12:746795. doi: 10.3389/fmicb.2021.746795. PMID: 34777295; PMCID: PMC8581659. 

Lawson LD, Hunsaker SM. Allicin Bioavailability and Bioequivalence from Garlic Supplements and Garlic Foods. Nutrients. 2018 Jun 24;10(7):812. doi: 10.3390/nu10070812. PMID: 29937536; PMCID: PMC6073756. 

Harunobu Amagase and others, Intake of Garlic and Its Bioactive Components, The Journal of Nutrition, Volume 131, Issue 3, March 2001, Pages 955S–962S, https://doi.org/10.1093/jn/131.3.955S 

Taghavi MR, Tavanaei Tamanaei T, Oghazian MB, Tavana E, Mollazadeh S, Niloofar P, Oghazian S, Hoseinzadeh A, Hesari A, Ansari Mohseni M, Rezaei S, Haresabadi M. Effectiveness of Fortified Garlic Extract Oral Capsules as Adjuvant Therapy in Hospitalized Patients with Coronavirus Disease 2019: A Triple-Blind Randomized Controlled Clinical Trial. Curr Ther Res Clin Exp. 2023;98:100699. doi: 10.1016/j.curtheres.2023.100699. Epub 2023 Mar 14. PMID: 36998289; PMCID: PMC10011030.

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