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Botanical names:
Allium sativum

Parts Used & Where Grown

Garlic has been used since time immemorial as a culinary spice and medicinal herb. Garlic has been cultivated in the Middle East for more than 5,000 years and has been an important part of Traditional Chinese Medicine. The region with the largest commercial garlic production is central California. China is also a supplier of commercial garlic. The bulb is used medicinally.

What Are Star Ratings?

This supplement has been used in connection with the following health conditions:

Used for Why
3 Stars
900 mg daily of a powder standardized for 0.6% allicin
Garlic has been shown to slow down the process of the arteries hardening. Aged garlic extract has been shown to prevent oxidation of LDL ("bad") cholesterol, a significant factor in atherosclerosis development.

Garlic has been shown to prevent atherosclerosis in a four-year double-blind trial. The preparation used, standardized for 0.6% allicin content, provided 900 mg of garlic powder per day. The people in this trial were 50 to 80 years old, and the benefits were most notable in women. This trial points to the long-term benefits of garlic to both prevent and possibly slow the progression of atherosclerosis in people at risk.

Garlic has also lowered cholesterol levels in double-blind research, though more recently, some double-blind trials have not found garlic to be effective. Some of the negative trials have flaws in their design. Nonetheless, the relationship between garlic and cholesterol-lowering is somewhat unclear.

Garlic has also been shown to prevent excessive platelet adhesion (stickiness) in humans. Allicin, often considered the main active component of garlic, is not alone in this action. The constituent known as ajoene has also shown beneficial effects on platelets. Aged garlic extract, but not raw garlic, has been shown, to prevent oxidation of LDL cholesterol in humans, an event believed to be a significant factor in the development of atherosclerosis.

Garlic and ginkgo also decrease excessive blood coagulation. Both have been shown in double-blind and other controlled trials to decrease the overactive coagulation of blood that may contribute to atherosclerosis.

Numerous medicinal plants and plant compounds have demonstrated an ability to protect LDL cholesterol from being damaged by free radicals. Garlic, ginkgo, and guggul are of particular note in this regard. Garlic and ginkgo have been most convincingly shown to protect LDL cholesterol in humans.

3 Stars
High Cholesterol
300 to 900 mg a day of garlic powder
Taking garlic can improve cholesterol levels and help prevent heart disease.
Numerous randomized controlled trials and meta-analyses have found garlic can reduce total and LDL-cholesterol levels and raise HDL-cholesterol levels. A meta-analysis of 14 randomized controlled trials noted garlic had positive effects on all types of cholesterol levels. Similarly, a meta-analysis that included data from 29 randomized controlled trials with a total of almost 2,300 participants found treatment with garlic for two months or longer reduced total cholesterol by 8% and LDL-cholesterol by 10%, although HDL-cholesterol levels were only slightly improved. One meta-analysis concluded garlic improved lipid profiles in people with type 2 diabetes after pooling findings from 39 randomized controlled trials. The majority of clinical trials in these meta-analyses used garlic powder at doses of 300–900 mg per day, but some used garlic oil, aged garlic extract, or raw garlic. In addition to inhibiting cholesterol synthesis in the liver, garlic has been found to reduce oxidation of LDL-cholesterol, lower blood pressure, and decrease the risk of blood clots, lowering the risks of atherosclerosis and cardiovascular events.
3 Stars
600 to 1,200 mg of garlic extract daily
Taking garlic may improve heart and blood vessel health and lower high blood pressure.

supplements, in doses ranging from 600–1,200 mg per day, have consistently been shown in randomized controlled trials to lower high blood pressure to a degree that is comparable to anti-hypertensive medications. One randomized controlled trial that included 88 participants with high blood pressure found treatment with 1,200 mg of aged garlic extract daily for 12 weeks reduced systolic blood pressure by an average of 5 mmHg. The trial identified a subgroup of 29 responders to garlic therapy whose blood pressure dropped by more than 3%; in this subgroup, systolic blood pressure was reduced by an average of 11.5 mmHg and diastolic blood pressure by 6.3 mmHg. Another trial found garlic extract lowered blood pressure in hypertensive patients with severe coronary artery disease: the trial included 56 participants with severe coronary artery disease who were given 800 mg of garlic extract per day or placebo for three months. Although the effect of garlic on blood pressure was not significant overall, in the 18 participants with baseline hypertension, garlic lowered blood pressure significantly more than placebo. Furthermore, garlic extract has been found to reduce arterial stiffness, improve blood glucose control, lower high cholesterol levels, decrease blood clot risk, and improve gut microbial balance, and may reduce the risks of heart attack and stroke.

Fresh garlic may also help lower high blood pressure: In an open trial, 40 participants with metabolic syndrome were given raw crushed garlic in an amount based on body weight (100 mg per kg body weight twice daily). After four weeks, blood pressures were reduced, and other markers of metabolic health, including waist circumference, triglyceride levels, fasting glucose levels, and cholesterol levels were improved. A six-year observational study found those who eat the largest amount of allium vegetables such as garlic and onion were less likely to develop high blood pressure, chronic kidney disease, and cardiovascular events.

3 Stars
Rub cut clove onto area nightly and cover until morning, or apply oil-soluble extract twice per day
Studies have shown topically applied garlic to be effective at clearing common warts.

In a preliminary trial, topical application of cloves was used successfully to treat warts in a group of children. A clove was cut in half each night and the flat edge of the clove was rubbed onto each of the warts, carefully cleaning the surrounding areas, so as not to spread any garlic juice. The areas were covered overnight with Band-Aids or waterproof tape and were washed in the morning. In all cases, the warts cleared completely after an average of nine weeks. In another study, 23 people with warts applied an oil-soluble garlic extract twice a day to the warts. Complete recovery was seen in every case after one to two weeks. A water-soluble garlic extract was less effective. Side effects after application of the oil-soluble extract included blistering, redness, burning, and increased pigmentation of the skin around the application area, which usually disappeared completely in one to two weeks. Zinc oxide ointment was applied to the surrounding normal skin in all cases in an attempt to prevent these side effects.

2 Stars
Benign Prostatic Hyperplasia
1 ml aged extract per 2.2 lbs (1 kg) of body weight daily
A special garlic extract (Kastamonu Garlic) reduced prostate size and significantly improved urinary symptoms in one study.

In many parts of Europe, herbal supplements are considered standard medical treatment for BPH. Although herbs for BPH are available without prescription, men wishing to take them should be monitored by a physician.

In a preliminary study, supplementation with a special aged garlic extract (Kastamonu Garlic) in the amount of 1 ml per 2.2 pounds of body weight per day for one month resulted in a 32% reduction in the size of the prostate gland and a significant improvement in urinary symptoms. It is not known whether other forms of garlic would have the same effect.

2 Stars
Breast-Feeding Support
Follow label instructions
Infants have been shown in some studies to nurse longer when their mothers ate garlic. However, some infants may develop colic from garlic in breast milk.

Numerous herbs are used traditionally around the world to promote production of breast milk. Herbs that promote milk production and flow are known as galactagogues. Stinging nettle (Urtica dioica) enriches and increases the flow of breast milk and restores the mother’s energy following childbirth.Vitex (Vitex agnus castus) is one of the best-recognized herbs in Europe for promoting lactation. An older German clinical trial found that 15 drops of a vitex tincture three times per day could increase the amount of milk produced by mothers with or without pregnancy complications compared with mothers given vitamin B1 or nothing. Vitex should not be taken during pregnancy. Goat’s rue (Galega officinalis) also has a history of use in Europe for supporting breast-feeding. Taking 1 teaspoon of goat’s rue tincture three times per day is considered by European practitioners to be helpful in increasing milk volume. Studies are as yet lacking to support the use of goat’s rue as a galactagogue. In two preliminary trials, infants have been shown to nurse longer when their mothers ate than when their mothers took placebos. However, some infants may develop colic if they consume garlic in breast milk.

2 Stars
Common Cold and Sore Throat
Follow label instructions to take a product containing stabilized allicin
In one study, taking garlic during the winter months reduced the occurrence and duration of colds.

In a double-blind trial, participants took one capsule per day of a placebo or a supplement that contained stabilized allicin (the amount of garlic per capsule was not specified) for 12 weeks between November and February. During that time, the garlic group had 63% fewer colds and 70% fewer days ill than did the placebo group. In another double-blind study of healthy volunteers, supplementing with 2.6 grams per day of an aged-garlic extract for 90 days decreased by 58% the number of days on which severe cold or influenza symptoms occurred.

2 Stars
High Triglycerides
600 to 900 mg daily of a concentrate standardized for 5,000 to 6,000 mcg of allicin
Supplementing with garlic may help keep triglyceride levels in check.

Reports on many clinical trials of performed until 1998 suggested that triglycerides were lowered by an average of 8–27% and cholesterol by 9–12% over a one- to four-month period. Most of these trials used 600–900 mg per day of a garlic supplement standardized to alliin content and allicin potential. More recently, however, three double-blind clinical trials have found garlic to have minimal success in lowering triglycerides and cholesterol. One negative trial has been criticized for using a steam distilled garlic “oil” that has no track record for this purpose, while the others used the same standardized garlic products as the previous positive clinical trials. Based on these findings, the use of garlic should not be considered a primary approach to lowering high triglycerides and cholesterol.

Odor-controlled, enteric-coated garlic tablets standardized for allicin content can be taken in the amount of 900 mg daily (providing 5,000–6,000 mcg of allicin), divided into two or three daily portions.

2 Stars
2.6 grams per day
Healthy volunteers who supplemented with an aged-garlic extract for 90 days decreased the number of days on which severe cold or influenza symptoms occurred by 58%.
In a double-blind study of healthy volunteers, supplementing with 2.6 grams per day of an aged-garlic extract for 90 days decreased by 58% the number of days on which severe cold or influenza symptoms occurred.
2 Stars
Intermittent Claudication
400 mg of a standardized extract twice per day
In one study, people given a garlic powder extract could walk a significantly greater distance than those given a placebo.

A standardized extract of has been tested as a treatment for intermittent claudication. In a double-blind trial, the increase in walking distance was significantly greater in people receiving garlic powder extract (400 mg twice per day for 12 weeks) than in those given a placebo.

1 Star
Athlete’s Foot
Refer to label instructions
The compound ajoene, found in garlic, is an antifungal agent that has been shown to be effective against athlete’s foot. Crushed, raw garlic applied topically may also be effective.

The compound known as ajoene, found in , is an antifungal agent. In a group of 34 people using a 0.4% ajoene cream applied once per day, 79% of them saw complete clearing of athlete’s foot after one week; the rest saw complete clearing within two weeks. All participants remained cured three months later. One trial found a 1% ajoene cream to be more effective than the standard topical drug terbinafine for treating athlete’s foot. Ajoene cream is not yet available commercially, but topical application of crushed, raw garlic may be a potential alternative application.

1 Star
Chronic Candidiasis
Refer to label instructions
Garlic has been shown to have significant anti-Candida activity.

has demonstrated significant antifungal activity against C. albicans in both animal and test tube studies. Greater anti-Candida activity has resulted from exposing Candida to garlic, than to nystatin—the most common prescription drug used to fight Candida. No clinical studies of garlic in the treatment of candidiasis have yet been conducted. However, some doctors suggest an intake equal to approximately one clove (4 grams) of fresh garlic per day; this would equal consumption of a garlic tablet that provides a total allicin potential of 4,000 to 5,000 mcg.

1 Star
Ear Infections
Refer to label instructions
Ear drops with mullein, St. John’s wort, and garlic in an oil or glycerin base are traditional remedies used to alleviate symptoms, particularly pain, during acute ear infections.

Ear drops with mullein, St. John’s wort, and in an oil or glycerin base are traditional remedies used to alleviate symptoms, particularly pain, during acute ear infections. No clinical trials have investigated the effects of these herbs in people with ear infections. Moreover, oil preparations may obscure a physician’s view of the ear drum and should only be used with a healthcare professional’s directions.

1 Star
HIV and AIDS Support
Refer to label instructions
Garlic may help combat opportunistic infections. In one trial, an aged garlic extract reduced the number of infections and relieved diarrhea in a group of patients with AIDS.

may assist in combating opportunistic infections. In one trial, administration of an aged garlic extract reduced the number of infections and relieved diarrhea in a group of patients with AIDS. Garlic’s active constituents have also been shown to kill HIV in the test tube, though these results have not been confirmed in human trials.

1 Star
Refer to label instructions
Garlic is an herb that directly attack microbes.

Herbs that directly attack microbes include the following: chaparral, eucalyptus, , green tea, lemon balm (antiviral), lomatium, myrrh, olive leaf, onion, oregano, pau d’arco (antifungal), rosemary, sage, sandalwood, St. John’s wort, tea tree oil, thyme, and usnea.

1 Star
Refer to label instructions
Garlic has been shown to kill parasites, including amoeba and hookworm, in test tubes and in animals. Other studies support the use of garlic to treat roundworm, pinworm, and hookworm.

has been demonstrated to kill parasites, including amoeba and hookworm, in test tubes and in animals. Older studies in humans support the use of garlic to treat roundworm, pinworm, and hookworm. However, due to a lack of clinical trials, the amount of garlic needed to treat intestinal parasites in humans is not known.

1 Star
Peptic Ulcer
Refer to label instructions
Garlic has been reported to have anti-Helicobacter activity in test-tube studies and may be helpful for peptic ulcers.

has been reported to have anti-Helicobacter activity in test-tube studies. In a preliminary trial, garlic supplementation (300 mg in tablets three times daily for eight weeks) failed to eradicate H. pylori in participants with active infections. In another preliminary trial, participants with active H. pylori infections added 10 sliced cloves of garlic to a meal. The addition of garlic failed to inhibit the growth of the organism. Further trials using garlic extracts are needed to validate the anti-Helicobacter activity of garlic observed in test tubes. Until then, evidence to support the use of garlic for H. pylori-related peptic ulcers remains weak.

1 Star
Sickle Cell Anemia
Refer to label instructions
In one trial, patients with sickle cell anemia who were given folic acid plus aged garlic extract, vitamin C, and vitamin E saw significant improvement and less painful crises.

In a preliminary trial, 20 patients with sickle cell anemia were given either 1 mg of folic acid per day or folic acid plus 6 grams of aged extract, 6 grams of vitamin C, and 1,200 mg of vitamin E per day for six months. Patients taking the combination had a significant improvement in their hematocrit (an index of anemia) and less painful crises than those taking just folic acid.

Traditional Use (May Not Be Supported by Scientific Studies)

Garlic is mentioned in the Bible and the Talmud. Hippocrates, Galen, Pliny the Elder, and Dioscorides all mention the use of garlic for many conditions, including parasites, respiratory problems, poor digestion, and low energy. Its use in China was first mentioned in A.D. 510. Louis Pasteur studied the antibacterial action of garlic in 1858.

How It Works

Botanical names:
Allium sativum

How It Works

The sulfur compound allicin, produced by crushing or chewing fresh garlic or by taking powdered garlic products with allicin potential, in turn produces other sulfur compounds: ajoene, allyl sulfides, and vinyldithiins.1 Aged garlic products lack allicin, but may have activity due to the presence of S-allylcysteine.

Many publications have shown that garlic supports the cardiovascular system. While earlier trials suggest it may mildly lower cholesterol and triglyceride levels in the blood,2, 3, 4 more recent trials found garlic to have minimal success in lowering cholesterol and triglycerides.5, 6, 7 Garlic also inhibits platelet stickiness (aggregation) and increases fibrinolysis,8 which results in a slowing of blood coagulation. It is mildly antihypertensive9 and has antioxidant activity.10

Garlic’s cardiovascular protective effects were illustrated in a four-year clinical trial on people 50–80 years old with atherosclerosis.11 It was found that consumption of 900 mg of a standardized garlic supplement reduced arterial plaque formation by 5–18%. The benefits were most notable in women.

In test tube studies garlic has been found to have antibacterial, antiviral, and antifungal activity.12 However, these actions are less clear in humans and do not suggest that garlic is a substitute for antibiotics or antifungal medications.

Human population studies suggest that eating garlic regularly reduces the risk of esophageal, stomach, and colon cancer.13, 14 This may be partly due to garlic’s ability to reduce the formation of carcinogenic compounds.

How to Use It

People who wish to consume garlic and have no aversion to its odor can chew from one to two whole cloves of raw garlic daily. For those who prefer it with less odor, enteric-coated tablets or capsules with approximately 1.3% allin are available. Clinical trials have used 600–900 mg (delivering approximately 5,000–6,000 mcg of allicin potential) per day in two or three divided amounts.15, 16 Aged-garlic extracts have been studied in amounts ranging from 2.4–7.2 grams per day.


Botanical names:
Allium sativum

Interactions with Supplements, Foods, & Other Compounds

At the time of writing, there were no well-known supplement or food interactions with this supplement.

Interactions with Medicines

Certain medicines interact with this supplement.

Types of interactions: Beneficial Adverse Check

Replenish Depleted Nutrients

  • none

Reduce Side Effects

  • none

Support Medicine

  • Dipyridamole

    A test tube study has shown ajoene, a compound found in garlic that prevents platelet clumping, enhances the beneficial action of dipyridamole on human platelets. Controlled research is needed to determine whether taking garlic supplements together with dipyridamole might enhance the effectiveness of either compound taken alone.

Reduces Effectiveness

  • Chlorzoxazone

    Test tube studies show that watercress, , tea, and cruciferous vegetables, such as Brussels sprouts, broccoli, and Chinese cabbage, block the breakdown of chlorzoxazone into inactive compounds. Controlled human research is needed to determine whether these interactions are important in people taking chlorzoxazone.

Potential Negative Interaction

  • Ticlopidine

    Garlic (Allium sativum) has been shown to help prevent atherosclerosis (hardening of the arteries), perhaps by reducing the ability of platelets to stick together. Interfering with the action of platelets results in an increase in the tendency toward bleeding and in theory could dangerously enhance the effect of ticlopidine. Standardized extracts of garlic have been associated with bleeding in people only on rare occasions. People taking ticlopidine should consult with a doctor before taking products containing standardized extracts of garlic or eating more than one clove of garlic daily.

  • Warfarin

    Garlic (Allium sativum) has been shown to help prevent atherosclerosis (hardening of the arteries), perhaps by reducing the ability of platelets to stick together. This can result in an increase in the tendency toward bleeding. Standardized extracts have, on rare occasions, been associated with bleeding in people. Garlic extracts have also been associated with two human cases of increased warfarin activity. The extracts were not definitively shown to be the cause of the problem. People taking warfarin should consult with a doctor before taking products containing standardized extracts of garlic or eating more than one clove of garlic daily.

Explanation Required

  • none

The Drug-Nutrient Interactions table may not include every possible interaction. Taking medicines with meals, on an empty stomach, or with alcohol may influence their effects. For details, refer to the manufacturers’ package information as these are not covered in this table. If you take medications, always discuss the potential risks and benefits of adding a supplement with your doctor or pharmacist.

Side Effects

Botanical names:
Allium sativum

Side Effects

At the time of writing, there were no well-known side effects caused by this supplement.


1. Koch HP, Lawson LD (eds). Garlic: The Science and Therapeutic Application of Allium sativaum L and Related Species, 2d ed. Baltimore: Williams and Wilkins, 1996, 62-4.

2. Warshafsky S, Kamer R, Sivak S. Effect of garlic on total serum cholesterol: A meta-analysis. Ann Int Med 1993;119(7)599-605.

3. Silagy C, Neil A. Garlic as a lipid-lowering agent—a meta-analysis. J R Coll Phys London 1994;28(1):39-45.

4. Neil HA, Silagy CA, Lancaster T, et al. Garlic powder in the treatment of moderate hyperlipidaemia: A controlled trial and a meta-analysis. J R Coll Phys 1996;30:329-34.

5. McCrindle BW, Helden E, Conner WT. Garlic extract therapy in children with hypercholesterolemia. Arch Pediatr Adolesc Med 1998;152:1089-94.

6. Isaacsohn JL, Moser M, Stein EA, et al. Garlic powder and plasma lipids and lipoproteins. Arch Intern Med 1998;158:1189-94.

7. Berthold HK, Sudhop T, von Bergmann K. Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism. JAMA 1998;279:1900-2.

8. Legnani C, Frascaro M, Guazzaloca G, et al. Effects of a dried garlic preparation on fibrinolysis and platelet aggregation in healthy subjects. Arzneim-Forsch Drug Res 1993;43:119-22.

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

10. Kleijnen J, Knipschild P, Ter Riet G. Garlic, onion and cardiovascular risk factors: A review of the evidence from human experiments with emphasis on commercially available preparations. Br J Clin Pharmacol 1989;28:535-44.

11. Koscielny J, Klüendorf D, Latza R, et al. The antiatherosclerotic effect of Allium sativum. Atherosclerosis 1999;144:237-49.

12. Hughes BG, Lawson LD. Antimicrobial effects of Allium sativum L. (garlic), Allium ampeloprasum L. (elephant garlic) and Allium cepa L. (onion), garlic compounds and commercial garlic supplement products. Phytother Res 1991;5:154-8.

13. Dorant E, van der Brandt PA, et al. Garlic and its significance for the prevention of cancer in humans: A critical view. Br J Cancer 1993;67:424-9 [review].

14. Fleishauer AT, Poole C, Arab L. Garlic consumption and cancer prevention: meta-analyses of colorectal and stomach cancers. Am J Clin Nutr 2000;72:1047-52.

15. Brown DJ. Herbal Prescriptions for Better Health. Rocklin, CA: Prima Publishing, 1996, 97-109.

16. Blumenthal M, Busse WR, Goldberg A, et al. (eds). The Complete Commission E Monographs: Therapeutic Guide to Herbal Medicines. Boston, MA: Integrative Medicine Communications, 1998, 134.

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How It Works

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