Garlic (Allium sativum L.)
  
Garlic (Allium sativum L.)
Background
Numerous controlled trials have examined the effects of oral garlic on serum lipids. Most studies have been small (<100 subjects), with poorly described design and results, and most have reported non-significant modest benefits. Several overlapping meta-analyses have pooled these studies, suggesting that non-enteric-coated tablets containing dehydrated garlic powder (standardized to 1.3% alliin) elicit modest reductions in total cholesterol vs. placebo (<20mg/dL) in the short term (4-12 weeks), with unclear effects after 20 weeks. Small reductions in low-density lipoprotein (LDL) (by <10mg/dL) and triglycerides (by <20mg/dL) may also occur in the short-term, although results have been variable. High-density lipoprotein (HDL) levels are not significantly affected. Long-term effects on lipids or cardiovascular morbidity and mortality remain unknown. Other preparations (such a enteric-coated or raw garlic) have not been well studied.
Small reductions in blood pressure (<10mmHg), inhibition of platelet aggregation, and enhancement of fibrinolytic activity have been reported, and may exert effects on cardiovascular outcomes, although evidence is preliminary in these areas.
Numerous case-control/population-based studies suggest that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of developing several types of cancer, including gastric and colorectal malignancies. However, prospective controlled trials are lacking.
Multiple cases of bleeding have been associated with garlic use, and caution is warranted in patients at risk of bleeding or prior to some surgical/dental procedures. Garlic does not appear to significantly affect blood glucose levels.
Synonyms
Alisat, allicin, Allii sativi bulbus, alliinase, allium, allyl mercaptan, alubosa elewe, Amaryllidaceae (family) , ayo-ishi, ayu, banlasun, camphor of the poor, clove garlic, da-suan, dai toan, dasuan, dawang, diallyl disulphide, diallyl sulfide, diallyl sulphide, dipropyl disulphide, dipropyl sulphide, dra thiam, foom, garlic clove, garlic corns, garlic extract, garlic oil, Gartenlauch, hom khaao, hom kia, hom thiam, hua thiam, kesumphin, kitunguu-sumu, knoblauch, kra thiam, Krathiam, krathiam cheen, krathiam khaao, Kwai®, Kyolic®, l'ail, lahsun, lai, la-juan, lasan, lashun, la-suan, lasun, lasuna, lauch, lay, layi, lehsun, lesun, Liliaceae (family), lobha, majo, naharu, nectar of the gods, Ninniku, pa-se-waa, poor man's treacle, rason, rasonam, rasun, rust treacle, rustic treacles, S-allylcysteine (SAC), seer, skordo, sluon, stinking rose, sudulunu, tafanuwa, ta-suam, ta-suan, tellagada, Tellagaddalu, thiam, thioallyl derivative, thiosulfinates, toi thum, tum, umbi bawang putih, vallaippundu, Velluli, vellulli, verum, vinyl dithiin.
Evidence
These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Uses based on scientific evidenceGrade*High cholesterol
Multiple studies in humans have reported small reductions in total blood cholesterol and low-density lipoproteins ("bad cholesterol") over short periods of time (4 to 12 weeks). It is not clear if there are benefits after this amount of time. Effects on high-density lipoproteins ("good cholesterol") are not clear. This remains an area of controversy. Well-designed and longer studies are needed in this area.
B
Familial hypercholesterolemia
Familial hypercholesterolemia is a genetic disorder in which very high cholesterol levels run in families. Research in children with an inherited form of high cholesterol suggests that garlic does not have a large effect in lowering cholesterol levels in these patients.
C
Atherosclerosis (hardening of the arteries)
Preliminary research in humans suggests that deposits of cholesterol in blood vessels may not grow as quickly in people who take garlic. It is not clear if this is due to the ability of garlic to lower cholesterol levels, or to other effects of garlic.
C
Peripheral vascular disease (blocked arteries in the legs)
Some human studies suggest that garlic may improve circulation in the legs by a small amount, but this issue remains unclear. Better-designed studies are needed.
C
Heart attack prevention in patients with known heart disease
It is not clear if garlic prevents future heart attacks in people who have already had a heart attack. The effects of garlic on cholesterol levels may be beneficial in such patients.
C
High blood pressure
Numerous human studies report that garlic can lower blood pressure by a small amount, but larger, well-designed studies are needed to confirm this possible effect.
C
Cancer prevention
It is not clear if eating garlic or taking garlic supplements regularly prevents cancer. More study is needed in this area before a conclusion can be drawn.
C
Anti-fungal (applied to the skin)
Several laboratory studies and historical reports describe the application of garlic to the skin to treat fungal infections, including yeast infections. However, little information on effectiveness is available. Take caution as garlic can cause severe burns and rash when applied to the skin of sensitive individuals.
C
Anti-platelet effects (blood thinning)
Laboratory and human studies suggest that garlic may reduce blood clotting due to effects on platelets in the blood. Excessive bleeding has been reported in people who take garlic supplements. It is not clear what doses of garlic have these effects, and caution is warranted in people with bleeding problems or taking drugs that increase the risk of bleeding. Additional safety studies are needed.
C
Tick repellant
No reliable scientific information is available on using garlic as a tick repellant.
C
Upper respiratory tract infection
Preliminary reports suggest that garlic may reduce the severity of upper respiratory tract infections. However, this has not been demonstrated in well-designed human studies.
C
Diabetes
Animal studies suggest that garlic may lower blood sugar and increase the release of insulin, but studies in humans do not confirm this effect.
D
Stomach ulcers caused by Helicobacter pylori bacteria
Early studies in humans show no effect of garlic on this condition.
D
* Key to grades
A: Strong scientific evidence for this use;
B: Good scientific evidence for this use;
C: Unclear scientific evidence for this use;
D: Fair scientific evidence against this use (it may not work);
F: Strong scientific evidence against this use (it likely does not work).
Uses based on tradition or theory
The below uses are based on tradition or scientific theories. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.
Abortion, age-related memory problems, AIDS, allergies, amoeba infections, antioxidant, antitoxin, anti-viral, aphrodisiac, arthritis, ascaridiasis (worms in the gut or liver), asthma, athlete's foot, bile secretion problems, bloody urine, bronchitis, cholera, claudication (leg pain due to poor blood flow), colds, cough, Cryptococcal meningitis, cytomegalovirus infection, dental pain, digestive aid, diphtheria, dysentery, diuretic (water pill), earache, fatigue, fever, gallstones, hair growth, headache, heart rhythm disorders, hemorrhoids, hepatopulmonary syndrome, HIV, immune system stimulation, induction of vomiting, influenza, kidney problems, kidney damage from antibiotics, liver health, malaria, mucous thinning, muscle spasms, nephrotic syndrome, obesity, parasites and worms, perspiration, pneumonia, psoriasis, Raynaud's disease, ringworm (, ), sedative, sinus decongestant, snake venom protection, spermicide, stomach ache, stomach acid reduction, stress (anxiety), stroke, thrush, toothache, traveler's diarrhea, tuberculosis, vaginal trichomoniasis, typhus, urinary tract infections, vaginal irritation, warts, well-being, whooping cough.
Dosing
The below doses are based on scientific research, publications, traditional use, or expert opinion. Many herbs and supplements have not been thoroughly tested, and safety and effectiveness may not be proven. Brands may be made differently, with variable ingredients, even within the same brand. The below doses may not apply to all products. You should read product labels, and discuss doses with a qualified healthcare provider before starting therapy.
Standardization
Standardization involves measuring the amount of certain chemicals in products to try to make different preparations similar to each other. It is not always known if the chemicals being measured are the "active" ingredients. Although allicin was once thought to be the major active ingredient in garlic, it now appears that additional compounds may contribute to the effects of garlic. The amounts of these compounds likely vary with the process used to manufacture the garlic product. Dried garlic powder is thought to have similar activity to fresh crushed garlic. However, garlic products prepared by other methods may not have as strong effects. For example, steam-distilled oils, oils from crushed garlic, and aged-garlic in alcohol may have less blood-thinning effects. The method of processing may be as important as the ingredients reported.
The standardized garlic powder product Kwai® has been used in numerous studies (manufactured by Lichtwer Pharma GmbH, Berlin, Germany). It is standardized to contain 1.3% allicin. Other research has used a standardized preparation containing 220 milligrams of garlic powder containing 2.4 milligrams of allicin. In the United States, pharmacy-grade garlic contains 0.3% (powdered) to 0.5% (fresh, dried) allicin, while in Europe, pharmacy-grade garlic must has at least 0.45% allicin.
Adults (18 years and older)
Tablets or capsules : 600 to 900 milligrams daily of non-coated, dehydrated garlic powder in three divided doses, standardized to 1.3% allicin content, has been used in human studies. The European Scientific Cooperative on Phytotherapy (ESCOP) recommends 3 to 5 milligrams allicin daily (1 clove or 0.5 to 1.0 gram dried powder) for prevention of atherosclerosis. The World Health Organization (WHO) recommends 2 to 5 grams fresh garlic, 0.4 to 1.2 grams of dried powder, 2 to 5 milligrams oil, 300 to 1000 milligrams of extract, or other formulations that are equal to 2 to 5 milligrams of allicin.
Oil : Human studies report the use of 4 to 12.3 milligrams of garlic oil by mouth daily. Steam-distilled oils, oil from crushed garlic, and aged-garlic in alcohol may be less effective for some uses, particularly as a blood thinner.
Tincture : The European Scientific Cooperative on Phytotherapy (ESCOP) recommends 2 to 4 grams of dried bulb or 2 to 4 milliliters of tincture (1:5 dilution in 45% ethanol), by mouth three times a day for upper respiratory tract infections.
Children (younger than 18 years)
Safety or effectiveness of garlic supplements has not been proven in children. One small study involving children with a hereditary form of high cholesterol showed no benefit from 900 milligrams of dehydrated garlic powder tablets (Kwai®) taken in three divided daily doses when compared to placebo (sugar pills). Garlic in amounts found in food is likely safe.
Safety
The U.S. Food and Drug Administration does not strictly regulate herbs and supplements. There is no guarantee of strength, purity or safety of products, and effects may vary. You should always read product labels. If you have a medical condition, or are taking other drugs, herbs, or supplements, you should speak with a qualified healthcare provider before starting a new therapy. Consult a healthcare provider immediately if you experience side effects.
Allergies
People with a known allergy to garlic, any of its ingredients, or to other members of the Liliaceae (lily) family, including hyacinth, tulip, onion, leek, and chives, should avoid garlic. Allergic reactions have been reported with garlic taken by mouth, inhaled, or applied to the skin. Some of these reactions are severe including throat swelling and difficulty breathing (anaphylaxis). It has been suggested that some cases of asthma from inhaling garlic may be due to mites on the garlic. Fresh garlic applied to the skin may be more likely to cause rashes than garlic extract.
Side Effects and Warnings
Bad breath, body odor, and allergic reactions are the most common reported side effects of garlic. Fresh garlic has caused rash or skin burns, both in people taking garlic therapy and in food preparers handling garlic. Most reactions improve after stopping garlic therapy. Garlic products should not be applied to the skin of infants or children due to multiple reports of skin burns, and should be used cautiously in adults. Other reported side effects include dizziness, increased sweating, fever, chills, asthma flares, and runny nose.
Bleeding is a potentially serious side effect of garlic use, including bleeding after surgery and spontaneous bleeding. Several cases of bleeding are reported, which may be due to effects of garlic on blood platelets, or to increased breakdown of blood clots (fibrinolysis). There is debate about the effects of garlic in people treated with warfarin (Coumadin®), but studies suggest that garlic does not alter the International Normalized Ratio (INR) values that are used to measure the effect of warfarin on blood thinning. Garlic should be stopped prior to some surgical or dental procedures due to an increased risk of bleeding. Caution is urged for people who have bleeding disorders or who take blood thinning medications (anticoagulants, aspirin/anti-platelet agents, non-steroidal anti-inflammatory drugs such as ibuprofen or naproxen) or herbs/supplements that may increase the risk of bleeding. Dosing adjustments may be necessary.
Animal studies suggest that garlic or its ingredients may lower blood sugar levels and increase the release of insulin. However, studies in humans do not show changes in blood sugar control in people with or without diabetes. Nonetheless, caution is advised in people with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood sugar levels may need to be monitored by a healthcare provider, and medication adjustments may be necessary. Informal reports describe low iodine absorption in the thyroid and low levels of thyroid hormone (hypothyroidism) with garlic supplementation. A few reports suggest that garlic and garlic-like plants may be linked to nodules or tumors of the thyroid. Reduced sperm counts have been reported in rats, but not in humans.
Dehydrated garlic preparations or raw garlic taken by mouth may cause burning of the mouth, bad breath, abdominal pain or fullness, poor appetite, gas, belching, nausea, vomiting, irritation of the stomach lining, changes in the bacteria in the gut, heartburn, diarrhea, or constipation. One report describes bowel obstruction in a man who ate a whole garlic bulb. Garlic should be used cautiously by people with stomach ulcers or who are prone to stomach irritation.
Multiple studies show a small reduction in blood cholesterol levels after garlic supplements are taken by mouth. Small reductions in blood pressure are also commonly reported. One case of heart attack is noted in a healthy man after taking a large amount of garlic by mouth.
Contamination of garlic products has been reported.
In Vancouver, British Columbia, a commercial preparation of chopped garlic was linked to botulism. One report describes overdose of colchicine and even death after meadow saffron ( Colchicum autumnale ) was mistaken for wild garlic ( Allium ursinium ).
Pregnancy and Breastfeeding
Garlic is likely safe during pregnancy in amounts usually eaten in food, based on historical use. However, garlic supplements or large amounts of garlic should be avoided during pregnancy due to a possible increased risk of bleeding. In addition, early animal studies suggest that garlic may cause contraction of the uterus. Many tinctures contain high levels of alcohol, and should be avoided during pregnancy.
Garlic is likely safe during breastfeeding in amounts usually eaten in food, based on historical use. However, some mothers who take garlic supplements report increased nursing time, milk odor, and reduced feeding by the infant. The safety of garlic supplements during breastfeeding is not known.
References
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November 01, 2002 
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