¿ Garlic

Home > Medical Reference > Complementary Medicine


Also listed as: Allium sativum


Garlic has been used as both food and medicine in many cultures for thousands of years, dating as far back as the time that the Egyptian pyramids were built. Later, gravediggers in early 18 th -century France drank a concoction of crushed garlic in wine they believed would protect them from the plague that killed many people in Europe. More recently, during both World Wars I and II, soldiers were given garlic to prevent gangrene. Today garlic is used to help prevent heart disease, including atherosclerosis (plaque buildup in the arteries that can block the flow of blood and possibly lead to heart attack or stroke), high cholesterol, high blood pressure, and to improve the immune system. Garlic may also protect against cancer.

While the science is not definitive at this point, much of the research is showing promise, and many clinicians continue to report improvements in the areas of cancer protection and heart-related risk factors for patients.

Garlic has antioxidant properties. Antioxidants help destroy free radicals -- particles that can damage cell membranes, interact with genetic material, and possibly contribute to the aging process as well as the development of a number of conditions including heart disease and cancer. Free radicals occur naturally in the body, but environmental toxins (including ultraviolet light, radiation, cigarette smoking, and air pollution) can also increase the number of these damaging particles. Antioxidants can neutralize free radicals and may reduce or even help prevent some of the damage they cause over time.

There are several types of garlic preparations. Most clinical studies have been performed on aged garlic extract (AGE) or enteric coated, dried garlic tablets. The conditions for which garlic is showing the most promise include:

Cardiovascular disease

Studies report that garlic consumption may decrease the progression of cardiovascular disease. Cardiovascular disease is associated with several factors, including raised serum total cholesterol, raised low density lipoprotein (LDL), and an increase in LDL oxidation (free radical damage), increased platelet aggregation (clumping), hypertension, and smoking. Garlic may help decrease LDL and total cholesterol levels while raising good cholesterols (high density lipoprotein, or HDL), decrease platelet aggregation (helps the blood flow more easily), and decrease blood pressure. Recently, garlic was also found to decrease two other markers of cardiovascular disease, homocysteine and C-reactive protein.

Garlic may also decrease blood pressure. Numerous studies have reported small reductions in systolic and diastolic blood pressure associated with the use of oral garlic.

Common cold

A well-designed study of nearly 150 people supports the value of garlic for preventing and treating the common cold. In this study, people received either garlic supplements or placebo for 12 weeks during "cold season" (between the months of November and February). Those who received the garlic had significantly fewer colds than those who received placebo. Plus, when faced with a cold, the symptoms lasted a much shorter time in those receiving garlic compared to those receiving placebo.


Garlic may strengthen the immune system and may help the body fight diseases such as cancer. Laboratory studies suggest that garlic may have some anti-cancer activity. Studies which follow groups of people over time suggest that people who have more raw or cooked garlic in their diet are less likely to have certain types of cancer, particularly colon and stomach cancers. Dietary garlic may also offer some protection against the development of breast, prostate, and laryngeal (throat) cancers.

While these results are promising, more research is needed to best understand whether dietary intake of garlic and other plants in the same family (such as onions, leeks, scallions, chives, and shallots) truly help to protect us from cancer.

Other uses

Plant Description

Garlic originally came from central Asia, and is now cultivated throughout the world. Garlic is a perennial that can grow 2 feet high or more. The most important part of this plant for medicinal purposes is the compound bulb. Each bulb is made up of 4 - 20 cloves, and each clove weighs about 1 gram. Garlic supplements can either be made from fresh, dried, aged, or garlic oil, and each may have different effects on the body.

What's It Made Of?

There are several important components of garlic that have been identified, and many more that have not. Alliin is an odorless sulfur-containing chemical derived from the amino acid cysteine. When garlic bulbs are crushed, alliin is converted into another compound called allicin. Allicin appears to be at least one of the primary active compounds that gives garlic its characteristic odor and many of its healing benefits. However, allicin is not absorbed effectively by the human body.

To combat this problem, aged garlic is fermented to break allicin down to usable compounds. These compounds are water-soluble sulfur compounds (S-allyl cysteine and others) and a small amount of oil-soluble sulfur compounds. The sulfur containing compounds in aged garlic give the supplement its reported benefits in cholesterol levels, heart disease, and cancer.

Available Forms

Garlic supplements are made from whole fresh garlic, dried, or freeze-dried garlic, garlic oil, and aged garlic extracts.

Not all garlic contains the same amount of active ingredients. There is a fairly wide variation in the amount of important components in both fresh garlic and commercial supplements. The amount of healthy compounds present depends on where the garlic is grown as well as how the product is prepared. Some experts believe that the wide variation in the quantity of active ingredients in garlic preparations explains why there is some variability in how well the substances lower cholesterol, improve blood pressure, and fight infection in different people.

Aged garlic products are made by fermenting garlic. Several clinical studies support the use of aged garlic for cardiovascular disease prevention. The manufacturers of aged garlic report that allicin, a compound commonly thought of as having healing effects in the body, is actually not absorbed efficiently by the body. Aged garlic is high in sulfur compounds that are absorbed and have beneficial effects on heart disease and health.

It is important to read the label on all garlic products carefully. It is best to use standardized garlic products to ensure that you are getting the most benefit. Also, follow the directions of a qualified health care provider with knowledge and experience in herbal medicine.

How to Take It


An appropriate medicinal dose for children has not been established. For this reason, use of garlic for health-related reasons in children should be directed by a qualified health care provider who has experience treating children with herbal remedies.


Whole garlic clove (as a food supplement): 2 - 4 grams per day of fresh, minced garlic clove (each clove is approximately 1 gram)

Aged garlic extract: 600 - 1,200 mg, daily in divided doses

Tablets of freeze-dried garlic: 200 mg, 2 tablets 3 times daily, standardized to 1.3% alliin or 0.6% allicin. Products may also be found standardized to contain 10 - 12 mg/Gm alliin and 4,000 mcg of total allicin potential (TAP).

Fluid extract (1:1 w/v): 4 mL, daily

Tincture (1:5 w/v): 20 mL, daily

Oil: 0.03 - 0.12 mL, 3 times daily


The use of herbs is a time-honored approach to strengthening the body and treating disease. Herbs, however, contain components that can trigger side effects and that can interact with other herbs, supplements, or medications. For these reasons, herbs should be taken with care, under the supervision of a health care provider qualified in the field of botanical medicine.

Garlic is considered to have very low toxicity and is listed as Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration.

Side effects from garlic include upset stomach, bloating, bad breath, body odor, and a stinging sensation on the skin from handling too much fresh or dried garlic. Handling garlic may also cause the appearance of skin lesions. Other, more rare side effects that have been reported by those taking garlic supplements include headache, fatigue, loss of appetite, muscle aches, dizziness described as vertigo (dizziness), and allergies such as an asthmatic reaction or contact dermatitis (skin rash).

Garlic has blood-thinning properties. This is also important to know if you are going to have surgery or deliver a baby. Too much garlic can increase your risk for bleeding during or after those procedures.

Possible Interactions

Garlic may alter the function of certain prescription medications. If you are being treated with any of the following medications, you should not use garlic supplements without first talking to your health care provider.

Antiplatelet medications -- Garlic may exaggerate the activity of medications that inhibit the action of platelets in the body. Examples of such medications include indomethacin, dipyridamole, Plavix, and aspirin.

Blood-thinning medications -- There have been reports of a possible interaction between garlic and warfarin that could increase the risk of bleeding in people taking this blood thinning medication. Therefore, when taking medications that may thin the blood, such as aspirin and warfarin, you not use garlic supplements unless you are under the supervision of a doctor.

Protease inhibitors -- Garlic may reduce blood levels of protease inhibitors, a medication used to treat people with the human immunodeficiency virus (HIV). Protease inhibitors inclue indinavir, ritinavir, and saquinavir.

Supporting Research

Ackermann RT, Mulrow CD, Ramirez G, Gardner CD, Morbidoni L, Lawrence VA. Garlic shows promise for improving some cardiovascular risk factors. Arch Intern Med . 2001;161:813-824.

Alder R, Lookinland S, Berry JA, et al. A systematic review of the effectiveness of garlic as an anti-hyperlipidemic agent. J Am Acad Nurse Pract . 2003;15(3):120-129.

Ang-Lee MK, Moss J, Yuan C-S. Herbal medicines and perioperative care [review]. JAMA . 2001;286(2):208-216.

Apitz-Castro R, Escalante J, Vargas R, et al. Ajoene, the antiplatelet principle of garlic, synergistically potentiates the antiaggregatory action of prostacyclin, forskolin, indomethacin, and dipyridamole on human platelets. Thromb Res . 1986;42(3):303-311.

Ashraf R, Aamir K, Shaikh AR, Ahmed T. Effects of garlic on dyslipidemia in patients with type 2 diabetes mellitus. J Ayub Med Coll Abbottabad . 2005;17(3):60-4.

Bailey C, Day C. Traditional plants medicine as treatments for diabetes. Diabetes Care . 1989;12:553-564.

Berthold HK, Sudhop T. Galic preparation for prevention of atherosclerosis. Curr Opin Lipidol . 1998;9(6):565-569.

Berthold HK, Sudhop T, von Bergmann K. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism. JAMA . 1998;279.

Blumenthal M, Goldberg A, Brinckmann J, eds. Herbal Medicine: Expanded Commission E Monographs . Newton, MA: Integrative Medicine Communications; 2000:139-148.

Caron MF, White CM. Evaluation of the antihyperlipidemic properties of dietary supplements. Pharmacotherapy . 2001;21(4):481-487.

Delaha EC, Garagusi VF. Inhibition of mycobacteria by garlic extract ( Alliumsativum ). Antimicrob Agents Chemother . 1985;27(4):485-486.

Dillon SA, Burmi RS, Lowe GM, et al. Antioxidant properties of aged garlic extract: an in vitro study incorporating human low density lipoprotein. Life Sci . 2003;72(14):1583-1594.

Dorant E, van den Brandt PA, Goldbohm RA. A prospective cohort study on the relationship between onion and leek consumption, garlic supplement use and the risk of colorectal carcinoma in The Netherlands. Carcinogenesis . 1996;17(3):477-484.

Dorant E, van den Brandt PA, Goldbohm RA. Allium vegetable consumption, garlic supplement intake, and female breast carcinoma incidence. Breast Cancer Res Treat . 1995;33(2):163-170.

Dorant E, van den Brandt PA, Goldbohm RA, Hermus RJ, Sturmans F. Garlic and its significance for the prevention of caner in humans: a critical view. Br J Cancer . 1993;67(3):424-429.

Fleischauer AT, Arab L. Garlic and cancer: a critical review of the epidemiologic literature. J Nutr . 2001;131:1032S-1040S.

Fleischauer AT, Poole C, Arab L. Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr . 2000;72:1047-1052.

Fugh-Berman A. Herb-drug interactions [review]. Lancet . 2000;355:134-138.

Fugh-Berman A. Herbs and dietary supplements in the prevention and treatment of cardiovascular disease. Prev Cardiol . 2000;3:24-32.

Garlic supplements can impede HIV medication. J Am Coll Surg . 2002;194(2):251.

Gallicano K, Foster B, Choudhri S. Effect of short-term administration of garlic supplements on single-dose ritonavir pharmacokinetics in healthy volunteers. Br J Clin Pharmacol . 2003;55(2):199-202.

Hassan ZM, Yaraee R, Zare N, et al. Immunomodulatory affect of R10 fraction of garlic extract on natural killer activity. Int Immunopharmacol . 2003;3(10-11):1483-1489.

Heck AM, DeWitt BA, Lukes AL. Potential interactions between alternative therapies and warfarin. Am J Health Syst Pharm . 2000;57(13):1221-1227.

Heron S, Yarnell E. Treating parasitic infections with botanical medicines. Altern Complement Ther . 1999;8:214-224.

Isaacsohn JL, Moser M, Stein EA, et al. Garlic powder and plasma lipids and lipoproteins: a multicenter, randomized, placebo-controlled trial. Arch Intern Med . 1998;158(11):1189-1194.

Izzo AA, Ernst E. Interactions between herbal medicines and prescribed drugs: a systematic review. Drugs . 2001;61(15):2163-2175.

Jain RC. Anti tubercular activity of garlic oil [letter]. Indian J Pathol Microbiol . 1998;41(1):131.

James JS. Garlic reduces squinavir blood levels 50%; may affect other drugs. AIDS Treat News . 2001;375:2-3.

Josling P. Preventing the common cold with a garlic supplement: a double blind, placebo-controlled survey. Adv Ther . 2001;18(4):189-193.

Kannar D, Wattanapenpaiboon N, Savige GS, Wahlqvist ML. Hypocholesterolemic effect of an enteric coated garlic supplement. J Am Coll Nutr . 2001;20(3):225-231.

Kasuga S, Uda N, Kyo E, et al. Pharmacologic activities of aged garlic extract in comparison with other garlic preparations. J Nutr . 2001;131(3s):1080S-1084S.

Kendler BS. Recent nutritional approaches to the prevention and therapy of cardiovascular disease. Prog Cardiovasc Nurs . 1997;12(3):3-23.

Koscielny J, Klubendorf D, Latza R, Schmitt R, Radtke H, Siegel G, Kiesewetter H. The antiatherosclerotic effect of Allium sativum. Atherosclerosis . 1999;144:237-249.

Larkin M. Surgery patients at risk for herb-anaesthesia interactions. Lancet . 1999;354(9187):1362.

LaValle JB, Krinsky DL, Hawkins EB, et al. Natural Therapeutics Pocket Guide . Hudson, OH: LexiComp; 2000:438-440.

Levi F, Pasche C, La Vecchia C, Lucchini F, Franceschi S. Food groups and colorectal cancer risk. Br J Cancer . 1999;79(7-8):1283-1287.

Loy MH, Rivlin RS. Garlic and cardiovascular disease. Nutr Clin Care . 2000;3(3):146-151.

Mantle D, Lennard TW, Pickering AT. Therapeutic applications of medicinal plants in the treatment of breast cancer: a review of their pharmacology, efficacy and tolerability. Adverse Drug React Toxicol Rev . 2000;19(3):223-240.

Markowitz JS, Devane CL, Chavin KD, et al. Effects of garlic (Allium sativum L.) supplementation on cytochrome P450 2D6 and 3A4 activity in healthy volunteers. Clin Pharmacol Ther . 2003;74(2):170-177.

Mashour NH, Lin GI, Frishman WH. Herbal medicine for the treatment of cardiovascular disease. Arch Intern Med . 1998;158:2225–2234.

Miller LG. Herbal medicinals: selected clinical considerations focusing on known or potential drug-herb interactions [review]. Arch Intern Med . 1998;158:2200-2211.

Milner JA. A historical perspective on garlic and cancer. J Nutr . 2001;131(3s):1027S-1031S.

Morelli V, Zoorob RJ. Alternative therapies: part I. Depression, diabetes, obesity. Am Fam Physician . 2000;62(5):1051-1060.

Munday JS, James KA, Fray LM, Kirkwood SW, Thompson KG. Daily supplementation with aged garlic extract, but not raw garlic, protects low density lipoprotein against in vitro oxidation. Atherosclerosis . 1999;143(2):399-404.

Nies LK, Cymbala AA, Kasten SL, et al., Complementary and alternative therapies for the management of dyslipidemia. Ann Pharmacother. 2006;40(11):1984-92.

Peleg A, Hershcovici T, Lipa R, et al. Effect of garlic on lipid profile and psychopathologic parameters in people with mild to moderate hypercholesterolemia. Isr Med Assoc . J 2003;5(9):637-640.

Pinto JT, Rivlin RS. Antiproliferative effects of allium derivatives from garlic. J Nutr . 2001;131(3S):1058S-1060S.

Rahman K. Historical perspective on garlic and cardiovascular disease. J Nutr . 2001;131(3s):977S-979S.

Rose KD, Croissant PD, Parliament CF, Levin MB. Spontaneous spinal epidural hematoma with associated platelet dysfunction from excessive garlic ingestion: a case report. Neurosurgery . 1990;26:880–882.

Sarrell EM, Mandelberg A, Cohen HA. Efficacy of naturopathic extracts in the management of ear pain associated with acute otitis media. Arch Pediatr Adolesc Med . 2001;155:796-799.

Salih BA, Abasiyanik FM. Does regular garlic intake affect the prevalence of Helicobacter pylori in asymptomatic subjects? Saudi Med J. 2003;24(8):842-845.

Siegers CP, Steffen B, Robke A, Pentz R. The effects of garlic preparations against human tumor cell proliferation. Phytomedicine . 1999;6(1):7-11.

Silagy CA, Neil AW. A meta-analysis of the effect of garlic on blood pressure. J Hypertens . 1994;12:463-468.

Spigelski D, Jones PJ. Efficacy of garlic supplementation in lowering serum cholesterol levels. Nutr Rev . 2001;59(7):236-241.

Steiner M, Khan AH, Holbert D, Lin RI. A double-blind crossover study in moderately hypercholesterolemic men that compared the effect of aged garlic extract and placebo administration on blood lipids. Am J Clin Nutr . 1996;64:866–870.

Steinmetz KA, Kushi LH, Bostick RM, Folsom AR, Potter JD. Vegetables, fruit, and colon cancer in the Iowa Women's Health Study. Am J Epidemiol . 1994;139(1):1-15.

Stevinson C, Pittler MH, Ernst E. Garlic for treating hypercholesterolemia. Ann Intern Med . 2000;133(6):420-429.

Superko HR, Krauss RM. Garlic powder, effect on plasma lipids, postprandial lipemia, low-density lipoprotein particle size, high-density lipoprotein subclass distribution and lipoprotein(a). J Am Coll Cardiol . 2000;35(2):321-326.

Wang HX, NG TB. Natural products with hypoglycemic, hypotensive, hypocholesterolemic, antiatherosclerotic and antithrombotic activities. Life Sci . 1999;65(25):2663-2677.

Witte JS, Longnecker MP, Bird CL, Lee ER, Frankl HD, Haile RW. Relation of vegetable, fruit, and grain consumption to colorectal adenomatous polyps. Am J Epidemiol . 1996;144(11):1015-1025.

Yeh YY, Liu L. Cholesterol-lowering effect of garlic extracts and organosulfur compounds: human and animal studies. J Nutr. 2001;131(3s):989S-993S.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial process . A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997-2007 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.