Garlic is taken orally to reduce high blood pressure, prevent heart disease and artherosclerosis, treat earaches, stimulate both the immune and circulatory systems and prevent cancer. Other applications include treating diabetes, arthritis, colds and flu, fighting stress and fatigue and maintaining healthy liver function (3).
Various official monographs list garlic as being both antibacterial and antimycotic (suppresses the growth of certain fungi) (1) (4) (5). Consequently garlic is administered to treat Helicobacter pylori infections (3) (7), and to inhibit the growth of Candida albicans, particularly in cases of recurrent yeast infections (6).
Parasitic worms are also apparently susceptible to garlic. The World Health Organization “Monographs on Selected Medicinal Plants” reports garlic has having been used to treat roundworm (Ascaris strongyloides) and hookworm (Ancylostoma caninum and Necator americanus) infestations, listing allicin as the active anthelmintic constituent (5).
The United States Department of Agriculture lists garlic as being a viricide on its Medicinal Plant Database (8).
What accounts for the antibacterial action of garlic? The garlic bulb contains an amino acid derivative called alliin, which is in fact odorless and contains no antibacterial properties. However when the garlic bulb is crushed or ground, alliin comes into contact with an enzyme (alliinase) that converts the alliin into allicin. Allicin is the reason for garlic’s distinctive odor, and is a potent antibacterial agent (2).
The use of garlic in history goes back thousands of years, with Hippocrates, Galen, Pliny the Elder, and Dioscorides all reporting its use for various conditions, including parasites, low energy, and respiratory and digestive disorders. Garlic’s reputation in Western medicine was established in 1858 when Louis Pasteur confirmed its antibacterial properties (6).
Traditional Chinese medicine has used garlic since at least A.D. 510 (6), and is still using it for amoebic and bacterial dysentery, tuberculosis, scalp ringworm and vaginal trichomoniasis.
Other folk medicine cultures have traditionally used garlic for treating colds and flu, fever, coughs, headache, hemorrhoids asthma, arteriosclerosis, low blood pressure, both hypoglycemia and hyperglycemia, cancer and as an aphrodisiac (amongst other things) (3) (4). Garlic has also been used to treat pinworms (4).
The anti-parasitic nature of garlic is demonstrated in the uses to which it has been applied in folk medicines around the world. For example, it has been traditionally used to treat parasitic worms in such diverse cultures as East Asia, India, Italy, North America, Peru, Saudi Arabia, Tunisia and the West Indies. Traditional practitioners in Greece have long used garlic extracts to protect against amoebic infections (10).
Laboratory tests (both in test tubes and in animals) have demonstrated that fresh garlic has antimicrobial activities (including antibacterial, antiviral, antifungal, anti-protozoal, and anti-parasitic) (3) (7) (10).
Particular activity against B. subtilis, E. coli, P. mirabilis, Salmonella typhi, methicillin-resistant Staph aureus, Staph faecalis, salmonella enteritidis, and V. cholerae have been noted (3) (7).
Bacteria shown to be susceptible to garlic in the test tube include species from Staphylococcus, Escherichia, Proteus, Salmonella, Providencia, Citrobacter, Klebsiella, Hafnia, Aeromonas, Vibrio and Bacillus genera (7). Human trials as well as in vitro studies have shown that garlic consumption is active against Mycobacterium tuberculosis (10).
An epidemiological study in China among 214 people from the Shandong province suggested that garlic consumption might have a protective effect against H. pylori infection and the development and progression of precancerous gastric lesions (9).
Fungi demonstrated to be susceptible to garlic in lab tests include the genera Microsporum, Epidermophyton, Trichophyton, Rhodotorula, Torulopsis, Trichosporon, Cryptococcus neoformans, and Candida, including Candida albicans. It is reported that garlic is more effective against pathogenic yeasts than nystatin, especially Candida albicans (3) (7) (10) (11).
Essential garlic oils were active on Entamoeba histolytica in clinical trials, confirming its potential for anti-amoebic activity (10).
Anti-protozoan activity has also been demonstrated in lab tests against Paramecium caudatum (14).
Garlic has also shown itself in lab tests to have several immune-enhancing effects (12).
Fresh garlic, garlic extracts, oil and oleoresin have been generally recognized as safe when consumed in amounts commonly found in food. Garlic has been used for medicinal purposes in clinical studies lasting up to 4 years without reports of significant toxicity. It is possibly unsafe when consumed in large amounts, with the American Herbal Products Association Botanical Safety Handbook claiming that high doses could be dangerous or even fatal for children. There are, however, no reported cases of significant adverse reactions or mortality in children associated with the ingestion of garlic (3).
There are no published reports of garlic adversely affecting pregnancy, although it would be wise to avoid consuming large amounts during these times. (Theoretically large amounts of garlic might act as an abortifacient causing uterine contractions.) There is a lack of reliable information dealing with the use of garlic while breastfeeding, but it has been generally accepted that consuming it in amounts commonly found in food would be safe (3).
Blumenthal M, et. al. ed.The Complete German Commission E Monographs: Therapeutic Guide to Herbal Medicines.Austin:American Botanical Council,1998.
Foster S, Tyler VE.Tyler’s Honest Herbal: A Sensible Guide to the Use of Herbs and Related Remedies.Fourth Edition.New York: The Haworth Herbal Press,1999.
Jellin JM, Batz F, Hitchens K.Natural Medicines Comprehensive Database.Third Edition.Stockton, California: Therapeutic Research Faculty, 2000.
Lueng AY, Foster S.Encyclopedia of Common Natural Ingredients Used in Food, Drugs and Cosmetics.Second Edition.New York, NY:Wiley & Sons,1996.
World Health Organization (WHO) (1999).Monographs on Selected Medicinal Plants.Volume 1.WHO,Geneva.
“Garlic ”Vitaminevi Herbal Index.1998.Accessed April 4, 2003.http://www.vitaminevi.com/Herb/Garlic.htm
Barnes J, Anderson LA, Phillipson JD,Herbal Medicines: A Guide for Healthcare Professionals.Second Edition.London: Pharmaceutical Press,2002.
“Garlic, Allium sativum.”United States Department of Agriculture (USDA) Medicinal Plant Database.Beltsville Agricultural Research Center.(Accessed May 30, 2003).http://www.pl.barc.usda.gov/plant_detail.cfm?plant_id=84
You WC, Zhang L, Gail MH, Ma JL, Chang YS, Blot WJ, Li JY, Zhao CL, Liu WD, Li HQ, Hu YR, Bravo JC, Correa P, Fraumeni JF Jr.Helicobacter pylori infection, garlic intake and precancerous lesions in a Chinese population at low risk of gastric cancer. Int J Epidemiol. 1998 Dec; 27 (6): 941-4.
Ross I.Medicinal Plants of the World: Chemical Constituents, Traditional and Modern Medicinal Uses. Totowa: Humana Press,1999.
Arora DS, Kaur J. Antimicrobial activity of spices. Int J Antimicrob Agents. 1999 Aug; 12 (3): 257-62