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garlic illustrationAlso Known As:

Aged Garlic Extract, Ail, Ajo, Allii Sativi Bulbus, Allium.

Scientific Name:

Allium sativum.

Family: Alliaceae or Liliaceae.

People Use This For:

Garlic is used for hypertension, hyperlipidemia, coronary heart disease, age-related vascular changes and atherosclerosis, myocardial infarction, earaches, chronic fatigue syndrome, and menstrual disorders. Garlic is also used to treat Helicobacter pylori infection. Other uses include treatment of allergic rhinitis, traveller's diarrhoea, colds, and flu. It is also used for immune system stimulation, and prevention and treatment of bacterial and fungal infections. Other uses include treatment of fever, coughs, headache, stomachache,sinus congestion, athlete's foot, gout, rheumatism, bronchitis, low blood pressure. It is also used as an aphrodisiac, for enhancing circulation, fighting stress and fatigue.

Topically, garlic oil is used for fungal infections.

Intravaginally, garlic is used alone or in combination with yogurt for vaginitis.

In foods and beverages, fresh garlic, garlic powder, and garlic oil are used as flavour components.



No concerns regarding safety when used orally and appropriately. Garlic has been used safely in clinical studies lasting up to 7 years without reports of significant toxicity.63,64,65,66,67,68,69,70,71,72,73,74,75,76

Children: Likely to be safe when used orally and appropriately, short-term. In one study, garlic extract 300 mg three times daily had side effects comparable to placebo when used in children ages 8-18 years for eight weeks.77 There are no case reports available of significant adverse events or mortality in children associated with ingestion of garlic.

Pregnancy and Lactation: No concerns regarding safety when used orally in amounts commonly found in foods.78



Atherosclerosis. Taking low doses of garlic powder orally, 300 mg per day, seems to lessen age-related decreases in aortic elasticity.

Higher doses of 900 mg per day seem to slow development of atherosclerosis in both aortic and

femoral arteries when used over a four-year period.79,72,73

Colorectal cancer. Several population studies suggest that increased dietary garlic consumption can decrease risk of developing colorectal cancer.84,80,81,82 However, garlic supplements do not seem to offer this benefit.83

Gastric cancer. Some evidence from population studies suggests that increasing dietary garlic consumption is associated with a decreased risk of developing stomach cancer.84,85,86

High Blood Pressure. Some clinical research shows that taking garlic orally can modestly reduce blood pressure in patients with hypertension and in people with normal blood pressure.87,88,89,63,75,90

In one analysis, garlic reduced systolic blood pressure by about 8% and diastolic blood pressure by about 7%, compared to placebo in patients with hypertension.90

Ringworm. Applying a garlic gel containing 0.6% ajoene seems to be as effective as terbinafine 1% cream.91

Tinea pedis (athlete's foot). Applying a garlic gel containing 1% ajoene seems to be more effective than 0.6% ajoene gel, and seems to beas effective as 1% terbinafine (Lamisil) for tinea pedis infections. Sixty days after completing one week of treatment 1% ajoene produces 100% mycologic cure, 0.6 % produces 72% mycologic cure, and 1% terbinafine produces 94% mycologic cure.92,93


Common cold. Preliminary clinical research suggests garlic might reduce the frequency and number of colds when taken prophylactically.94


Mechanism of Action:

The applicable part of garlic is the bulb. Garlic is mostly used for its antihyperlipidemic, antihypertensive, and antifungal effects. However, it is also reported to have antibacterial, antiparasite (worms), antiviral, antispasmodic, promotes sweating, expectorant, immunostimulant, and antithrombotic effects.95,96,97,98,99 Many of the pharmacological effects of garlic are attributed to the allicin, ajoene, and other organosulfur constituents such as S-allyl-L-cysteine.98


It's thought that the effectiveness of garlic products might to be determined by their ability to yield allicin, which in turn triggers production of other active constituents.100

Intact garlic cells in fresh garlic contain the odorless amino acid, alliin. When intact cells are broken, alliin comes intocontact with the enzyme alliinase in garlic, producing allicin, an unstable, odiferous compound.100,97 Fresh garlic contains approximately 1% alliin. One milligram of alliin is converted to 0.458mg allicin.101 Further conversion yields ajoene. The amount of allicin in garlic preparations is dependent upon the method of preparation. Processes that involve maceration of the garlic clove increase the activity of allicinase. Freeze-dried garlic may contain little or no allicin. To improve effectiveness, garlic preparations may be coated to protect the active constituents from degeneration

by stomach acid.102 Heat and steam distillation used to produce garlic oil from crushed garlic converts allicin to allyl sulfides which are also thought to have biological activity.100


Garlic is aged to reduce the content of other sulfur compounds and the odor commonly associated with garlic. The process to produce odorless aged garlic extract reduces the alliin content to only 3% of what is typically contained in fresh garlic.101

Aged garlic extract is usually standardized to S-allyl-L-cysteine, another major organosulfur constituent in garlic.95


In patients with hyperlipidemia, garlic might lower cholesterol levels by acting as a HMG-CoA reductase inhibitor (statin).103,104 There is some evidence the constituent S-allyl-L-cysteine may be a potent inhibitor of hepatic cholesterol synthesis.105


For age-related vascular changes and atherosclerosis, garlic is thought to be beneficial and protect vascular endothelial cells from injury by reducing oxidative stress, inhibiting low-density lipoprotein (LDL) oxidation, and through antithrombotic effects.106,107,98,108 There is evidence that LDL oxidation may be inhibited by the constituents S-allyl cysteine, S-allyl mercaptocysteine, alliin, allixin, and by N-acetyl-S-allyl cysteine, a metabolite of S-allyl cysteine.108 Garlic appears to prevent endothelial cell depletion of glutathione, which may be responsible for its antioxidant effects.106


Garlic powder and aged garlic preparations have been shown to have antiplatelet properties in both patients with cardiovascular disease and in healthy volunteers.109,95,96,110,111

Garlic has been found to have antithrombotic properties and can increase fibrinolytic activity,decrease platelet aggregation and adhesion, increase the prothrombin time (PT), and inhibit metabolic enzymes in platelets responsible for the conversion of arachidonic acid into prostaglandins and other products.95,96,98,112 Raw garlic seems to have more potent antiplatelet properties

than cooked garlic.113,114,115 Crushing garlic before cooking might prevent some of the loss of antiplatelet activity.115 Garlic oil does not appear to affect platelet aggregation.116


Garlic is thought to reduce blood pressure by causing smooth muscle relaxation and vasodilation by activating production of endothelium-derived relaxation factor (EDRF, nitric oxide).117


Garlic also seems to have humoral and cellular immunostimulant activity.


The constituents allicin and ajoene are thought to beresponsible for garlic's antifungal activity against ringworm infections.98,93 Fresh garlic, but not aged garlic, has shown activity against Escherichia coli, methicillin-resistant Staph aureus, salmonella enteritidis, and Candida albicans in the laboratory; it has been suggested as a food additive to prevent food poisoning.

118 Preliminary evidence suggests that garlic compounds might have activity against viruses


Adverse Reactions:

Orally, garlic has dose-relatedadverse effects, which most commonly include breath and body odour, mouth and gastrointestinal burning or irritation, heartburn, flatulence, nausea, vomiting, and diarrhoea. These effects can be more pronounced with consumption of raw garlic or in patients unaccustomed to eating garlic.78,65,101 Oral use of garlic can also cause changes to the intestinalflora,78 ,101 which might result in gastrointestinal upset. Garlic's effect on platelet function is well known, and can possibly increase the risk of bleeding.


Interactions with Herbs & Supplements:

Anticoagulatn/Antiplatelet Herbs and Supplements: Concomitant use of herbs that have constituents that might affect platelet aggregation could theoretically increase the risk of bleeding in some people. These herbs include angelica, clove, danshen, ginger, ginkgo, red clover, turmeric, vitamin E, willow, and others.109,95,96,110,111


Interactions with Drugs:

Anticoagulatn/Antiplatelet Drugs including Warfarin.

Cyclosporine: (transplant patients).

Isoniazid (TB treatment).

Saquinavir (HIV treatment).


Interactions with Foods:

None known.


Interactions with Lab Tests:

Blood Pressure: Garlic can lower blood pressure and blood pressure readings.87,88,89

Cholesterol: Garlic can lower serum cholesterol concentrations and test results.87,88,89

Clotting Studies.120


Interactions with Diseases or Conditions:

Bleeding Disorders:95,96,98 Contraindicated.

Gastrointestinal (GI) Irritation: Garlic can irritate the GI tract; dose related, resolves on stopping garlic.


Surgery: discontinue one to two weeks prior to scheduled surgery.121,101,122



Dr Clare’s Blends: 1gm/day


Specific References: GARLIC

63. 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;58:866-70.

64. Holzgartner H, Schmidt U, Kuhn U. Comparison of the efficacy and tolerance of a garlic preparation vs. bezafibrate. Arzneimittelforschung 1992;36:1473-7.

65. Jain AK, Vargas R, Gotzkowsky S, McMahon FG. Can garlic reduce levels of serum lipids? A controlled clinical study. Am J Med 1993;94:632-5. 66. Mader FH. Treatment of hyperlipidaemia with garlic-powder tablets. Evidence from the German Association of General Practitioners' multicentric placebo-controlled double-blind study. Arzneimittelforschung 1990;34:1111-6.

67. Rotzsch W, Richter V, Rassoul F, Walper A. [Postprandial lipemia under treatment with Allium sativum. Controlled double-blind study of subjects with reduced HDL2-cholesterol]. [Article in German]. Arzneimittelforschung 1992;36:1223-7.

68. Silagy C, Neil A. Garlic as a lipid lowering agent--a meta-analysis. J R Coll Physicians Lond 1994;28:33-39.

69. Vorberg G, Schneider B. Therapy with garlic: results of a placebo-controlled, double-blind study. Br J Clin Pract Symp Suppl 1990;69:7-11.

70. Adler AJ, Holub BJ. Effect of garlic and fish-oilsupplementation on serum lipid and lipoprotein concentrations in hypercholesterolemic men. Am J Clin Nutr 1997;59:445-44.

71. Morcos NC. Modulation of lipid profile by fish oil and garlic combination. J Natl Med Assoc 1997;89:673-8.

72. Breithaupt-Grogler K, Ling M, Boudoulas H, Belz GG. Protective effect of chronic garlic intake on elastic properties of aorta in the elderly.Circulation 1997;96:2649-49.

73. Koscielny J, Klussendorf D, Latza R, et al. The antiatherosclerotic effect of Allium sativum. Atherosclerosis 1999;144:237-43.

74. Stevinson C, Pittler MH, Ernst E. Garlic for treating hypercholesterolemia: a meta-analysis of randomized clinical trials. Ann Intern Med 2000;133:420-9.

75. Ackermann RT, Mulrow CD, Ramirez G, et al. Garlic shows promise for improving some cardiovascular risk factors.

Arch Intern Med 2001;161:813-18.

76. You WC, Brown LM, Zhang L, et al. Randomized double-blind factorial trial of three treatments to reduce the prevalence of precancerous gastric lesions. J Natl Cancer Inst 2006;98:974-83.

77. McCrindle BW, Helden E, Conner WT. Garlic extract therapy in children with hypercholesterolemia. Arch Pediatr Adolesc Med 1998;152:108 9-94.

78. Bloch AS. Pushing the Envelope of Nutrition Support: Complementary Therapies. Nutrition 2000;16:236-9.

79. Siegel G, Klubendorf D. The anti-atherosclerotic effect of Allium sativum: Statistics re-evaluated. Atherosclerosis 2000;150:437-8.

80. Steinmetz KA, Kushi LH, Bostick RM, et al. Vegetables, fruit, and colon cancer in the Iowa Women's Health Study. Am J Epidemiol 1994;139:1-15.

81. Witte JS, Longnecker MP, Bird CL, et al. Relation of vegetable, fruit, and grain consumption to colorectal adenomatous polyps. Am J Epidemiol 1996;144:1015-19.

82. Le Marchand L, Hankin JH, Wilkens LR, et al. Dietary fiber and colorectal cancer risk. Epidemiology 1997;8:658-59.

83. 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;17:477-84.

84. Fleischauer AT, Poole C, Arab L. Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr 2000;72:1047-46.

85. You WC, Blot WJ, Chang YS, et al. Allium vegetables and reduced risk of stomach cancer. J Natl Cancer Inst 1989; 81:162-4.

86. Takezaki T, Gao CM, Ding JH, et al. Comparative study of lifestyles of residents in high and low risk areas for gastric cancer in Jiangsu Province, China; with special reference to allium vegetables. J Epidemiol 1999;9:297-305.

87. Silagy CA, Neil HA. A meta-analysis of the effect of garlic on blood pressure. J Hypertension 1994;12:463-8.

88. McMahon FG, Vargas R. Can garlic lower blood pressure? A pilot study. Pharmacotherapy 1993;13:406-7.

89. Auer W, Eiber A, Hertkorn E, et al. Hypertension and hyperlipidaemia: garlic helps in mild cases. Br J Clin Pract

Symp Suppl 1990;69:3-6.

90. Ried K, Frank OR, Stocks NP, et al. Effect of garlic on blood pressure: A systematic review and meta-analysis. BMC Cardiovasc Disord 2008;8:13.

91. Ledezma E, Lopez JC, Marin P, et al. Ajoene in the topical short-term treatment of tinea cruris and tinea corporis in humans. Randomized comparative study with terbinafine. Arzneimittelforschung 1999;43:544-7.

92. Ledezma E, DeSousa L, Jorquera A, et al. Efficacyof ajoene, an organosulphur derived from garlic, in the short-term therapy of tinea pedis. Mycoses 1996;33:393-5.

93. Ledezma E, Marcano K, Jorquera A. Efficacy of ajoene in the treatment of tinea pedis: A double-blind and comparative study with terbinafine. J Am Acad Dermatol 2000;37:829-32.

94. Josling P. Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey. Adv Ther 2001;18:189-93.

95. Rahman K, Billington D. Dietary supplementation with aged garlic extract inhibits ADP-induced platelet aggregation in humans. J Nutr 2000;130:2662-5.

96. Steiner M, Li W. Aged garlic extract, a modulator of cardiovascular risk factors: a dose-finding study on the effects of AGE on platelet functions. J Nutr 2001;131:980S-4S.

97. Ankri S, Mirelman D. Antimicrobial properties ofallicin from garlic. Microbes Infect 1999;1:125-9.

98. M, Thomson M, Afzal M. Garlic and onions: their effect on eicosanoid metabolism and its

clinical relevance. Prostaglandins Leukot Essent Fatty Acids 2000;56:49-73.

99. Lamm DL, Riggs DR. The potential application ofallium sativum (garlic) for the treatment of bladder cancer. Urol Clin North Am 2000;21:157-56.

100. Zhang XH, Lowe D, Giles P, et al. Gender may affect the action of garlic oil on plasma cholesterol and glucose levels of normal subjects. J Nutr 2001;131:1471-8.

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

102. Staba EJ, Lash L, Staba JE. A commentary on the effects of garlic extraction and formulation on product composition. J Nutr 2001;131:1118S-9S.

103. Gebhardt R, Beck H. Differential inhibitory effects of garlic-derived organosulfur compounds on cholesterol biosynthesis in primary rat hepatocyte cultures. Lipids 1996;31:1269-76.

104. Qureshi AA, Din ZZ, Abuirmeileh N, et al. Suppression of avian hepatic lipid metabolism by solvent extracts of garlic: impact on serum lipids. J Nutr 1983;113:1746-49.

105. Yeh YY, Liu L. Cholesterol-lowering effect of garlic extracts and organosulfur compounds: human and animal studies. J Nutr 2001;131:989S-93S.

106. Ide N, Lau BH. Aged garlic extract attenuates intracellular oxidative stress. Phytomedicine 1999;6:125-31.

107. Dirsch VM, Kiemer AK, Wagner H, Vollmar AM. Effect of allicin and ajoene, two compounds of garlic, on inducible nitric oxide synthase. Atherosclerosis 1998;139:333-9.

108. Lau BH. Suppression of LDL oxidation by garlic. JNutr 2001;131:985S-8S.

109. Steiner M, Lin RS. Changes in platelet function and susceptibility of lipoproteins to oxidation associated with administration of aged garlic extract. J Cardiovasc Pharmacol 1998;31:904-8.

110. Kiesewetter H, Jung F, Jung EM, et al. Effect of garlic on platelet aggregation in patients with increased risk of juvenile ischaemic attack. Eur JClin Pharmacol 1993;39:333-6.

111. Legnani C, Frascaro M, Guazzaloca G, et al. Effects of a dried garlic preparation on fibrinolysis and platelet aggregation in healthy subjects. Arzneimittelforschung 1993;37:119-22.

112. Evans V. Herbs and the brain: friend or foe? The effects of ginkgo and garlic on warfarin use. J Neurosci Nurs 2000;32:229-32.

113. Chutani SK, Bordia A. The effect of fried versus raw garlic on fibrinolytic activity in man. Atherosclerosis 1981;32:417-21.

114. Ali M, Bordia T, Mustafa T. Effect of raw versus boiled aqueous extract of garlic and onion on platelet aggregation. Prostaglandins Leukot Essent Fatty Acids 1999;54:37-7.

115. Cavagnaro PF, Camargo A, Galmarini CR, Simon PW. Effect of cooking on garlic (Allium sativum l.) Antiplatelet

activity and thiosulfinates content. J Agric Food Chem 2007;49:1280-8.

116. Morris J, Burke V, Mori TA, et al. Effects of garlic extract on platelet aggregation: a randomized placebo-controlled double-blind study. Clin Exp Pharmacol Physiol 1995;22:414-7.

117. Pedraza-Chaverri J, Tapia E, Medina-Campos ON, et al. Garlic prevents hypertension induced by chronic inhibition

of nitric oxide synthesis. Life Sci 1998;56:71-7.

118. Sasaki J, Kita T, Ishita K, et al. Antibacterial activity of garlic powder against Escherichia coli O-157. J Nutr Sci Vitaminol (Tokyo) 1999;39:785-90.

119. Weber ND, Andersen DO, North JA, et al. In vitro virucidal effects of Allium sativum (garlic) extract and compounds. Planta Med 1992;52:417-17.

120. Sunter WH. Warfarin and garlic. Pharm J 1991;246:722.

121. Burnham BE. Garlic as a possible risk for postoperative bleeding. Plast Reconstr Surg 1995;95:213.

122. Carden SM, Good WV, Carden PA, Good RM. Garlic and the strabismus surgeon. Clin Experiment Ophthalmol 2002;30:303-4.

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