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Family: Amaryllidaceae, Alliaceae, or Liliaceae.
Garlic is a culinary herb cultivated worldwide. It is related to onion, leeks, and chives (6465). It is thought that garlic is native to Siberia, but was spread to other parts of the world over 5000 years ago (6465).
- Some evidence for use in patients with diabetes, atherosclerosis, hyperlipidemia, and hypertension, although any benefit is probably modest. Commonly used for the common cold, cancer, and other conditions, but there is no strong evidence to support these uses.
- Likely safe when used orally. Side effects may include breath and body odor, gastrointestinal symptoms, or dizziness. Some people may be allergic to garlic.
- Garlic might increase the risk of bleeding. Use caution in combination with anticoagulant/antiplatelet drugs, and avoid use in patients with bleeding disorders.
Also known as: Aged Garlic Extract, Ail, Ail Blanc, Ail Cultive, Ail Rocambole, Ajo, Alho, Allii Sativi Bulbus, Allium, Angio D’India, Camphor Of The Poor, Clove Garlic, Common Garlic, Da Suan, Echte Rokkenbolle, Echter Knoblauch, Garlic Oil, Knoblauch, Lahsun, Lasun, Lasuna, Maneul, Nectar Of The Gods, Ninniku, Ophio Garlic, Poor Man’s Treacle, Rason, Rocambole, Rockenbolle, Rust Treacle, Schlangenknoblauch, Serpent Garlic, Spanish Garlic, Stinking Rose, Suan, Thoum, Vitlok.
Throughout history, garlic has been used for commercial, culinary, mythical, and medicinal purposes. Around 2500 BC, garlic was used as currency in ancient Egyptian and ancient Middle Eastern cultures (6465). Use of garlic for culinary purposes is described in the Old Testament of the Bible (6465). Balkans used garlic to keep them safe from both vampires and witches, while people in other parts of Europe used garlic to protect against evil spirits (6465). Garlic was used in ancient Greece, Rome, Egypt, India, China, and Japan for various medical indications (51232).
The widespread contemporary use and scientific interest in garlic may stem from antibiotic applications by Louis Pasteur and Albert Schweitzer. Garlic was used during both World Wars to prevent gangrene (51505). Research on garlic began with study of its antibacterial activity in the 1930s, with subsequent investigations into cancer inhibition beginning in the late 1940s (51464).
People Use This For
Orally, garlic is used for hypertension, hypotension, hyperlipidemia, familial hypercholesterolemia, coronary heart disease (CHD), atherosclerosis, peripheral arterial disease (PAD), myocardial infarction, metabolic syndrome, obesity, earaches, chronic fatigue syndrome (CFS), and menstrual disorders. Garlic is also used orally for HIV-drug induced lipid disorders, hepatitis, hepatopulmonary syndrome, Helicobacter pylori infection, and gastritis. Garlic is used to prevent colorectal cancer, esophageal cancer, gastric cancer, breast cancer, lung cancer, multiple myeloma, to treat and prevent prostate cancer, and to treat bladder cancer. Other uses include treatment of benign prostatic hyperplasia (BPH), cystic fibrosis, diabetes, osteoarthritis, allergic rhinitis, traveler’s diarrhea, pre-eclampsia, vaginal candidiasis, swine flu, and flu. It is also used as a tick repellent, as a mosquito repellant, for prevention of the common cold, and for prevention and treatment of bacterial and fungal infections. Garlic is also used for athletic performance, exercise-induced muscle soreness, fibrocystic breast disease, scleroderma, lead toxicity, diarrhea, amoebic and bacterial dysentery, tuberculosis, bloody urine, diphtheria, whooping cough, scalp ringworm, hypersensitive teeth, and vaginal trichomoniasis. Other uses include treatment of fever, coughs, headache, stomachache, sinus congestion, gout, joint pain, hemorrhoids, asthma, bronchitis, shortness of breath, hypoglycemia, and snakebites. It is also used for stress and fatigue.
Topically, garlic oil is used for alopecia areata, oral mucositis, oropharyngeal candidiasis, vaginal candidiasis, tinea pedis, tinea corporis, tinea cruris, onychomycosis, warts, and corns.
Intravenously, garlic is used for angina.
Intravaginally, garlic is used for vaginal candidiasis.
In foods and beverages, fresh garlic, garlic powder, and garlic oil are used as flavor components.
LIKELY SAFE …when used orally and appropriately. Garlic has been used safely in clinical studies lasting up to 7 years without reports of significant toxicity (1873,4782,4783,4784,4785,4786,4787,4789,4790,4797)(4798,6457,6897,14447,96008,96009,96014,102016).
POSSIBLY SAFE …when used topically. Garlic-containing gels, lipid-soluble garlic extracts, garlic pastes, and garlic mouthwashes have been safely used in clinical research for up to 3 months (4766,4767,8019,15030,51330,51386,51466). However, garlic applied topically might cause severe skin irritation (585). …when used intravaginally. A vaginal cream containing garlic and thyme has been safely used nightly for 7 nights (88387).
CHILDREN: POSSIBLY 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 (4796). POSSIBLY UNSAFE …when used orally in large amounts. Some sources suggest that high doses of garlic could be dangerous or even fatal to children (12); however, the reason for this warning is not known. There are no case reports available of significant adverse events or mortality in children associated with ingestion of garlic. …when raw garlic is applied topically. Raw garlic might cause severe skin irritation when applied topically (585).
PREGNANCY: LIKELY SAFE …when used orally in amounts commonly found in foods (3319). POSSIBLY UNSAFE …when used orally in medicinal amounts. Garlic is reported to have abortifacient activity (11020). One study also suggests that garlic constituents are distributed to the amniotic fluid after a single dose of garlic (4828). However, there are no published reports of garlic adversely affecting pregnancy. In clinical research, garlic 800 mg daily was used during the third trimester of pregnancy with no reported adverse outcomes (9201,51626). There is insufficient reliable information available about the safety of topical garlic use during pregnancy.
LACTATION: POSSIBLY UNSAFE …when used orally in amounts greater than those commonly found in foods. Several small studies suggest that garlic constituents are secreted in breast milk, and that nursing infants of mothers consuming garlic are prone to extended nursing and an altered flavor in breast milk (3319,4829,4830). There is insufficient reliable information available about the safety of topical garlic use during lactation.
Atherosclerosis. Taking low doses of garlic powder orally, 300 mg daily, seems to lessen age-related decreases in aortic elasticity (4797,51595). Additionally, taking a specific time-released garlic powder supplement (Allicor, INAT-Farma) 150 mg twice daily for 24 months seems to reduce the rate of atherosclerosis progression, as measured by carotid intima-media thickness, compared to placebo in men with early evidence of carotid atherosclerosis (88394). Higher doses of 900 mg daily seem to slow development of atherosclerosis in both aortic and femoral arteries when used over a four-year period in women, but not in men (3315,4798). Some clinical research shows that taking a specific supplement (Kyolic, Total Heart Health, Formula 108, Wakunaga) containing aged garlic extract 250 mg plus vitamin B12 100 mcg, folic acid 300 mcg, vitamin B6 12.5 mg, and L-arginine 100 mg daily for 12 months significantly reduces coronary artery calcium progression and improves vascular function as measured by changes in white and brown epicardial adipose tissue in patients with a Framingham risk score of 10-20% without coronary artery disease (88385). Additional clinical research shows that taking four tablets of a combination product containing aged garlic extract 300 mg and coenzyme Q10 30 mg per tablet daily for one year significantly improves vascular elasticity endothelial function in firefighters facing high degrees of occupational stress (44225).
Diabetes. A 2015 analysis of results from seven clinical studies shows that taking garlic powder 600-1500 mg daily, garlic oil 8.2 mg daily, or aged garlic extract 1000 mg daily reduces fasting blood glucose levels by about 1.7 mg/dL compared to control in patients with diabetes. The greatest benefit is seen for patients with hyperglycemia at baseline, for interventions lasting at least 12 weeks, and for formulations consisting of garlic powder (96004). Specific garlic formulations used in the reviewed studies have included garlic powder tablets (Kwai, Lichtwer Pharmaceuticals) and time-released garlic powder tablets (Allicor, INAT-Farma) (51396,96004). The findings from this analysis are in contrast with the results from older analyses, which showed that garlic does not improve glycemic indices or lipid levels in patients with diabetes. Reasons for these discrepancies may relate to the fact that the older analyses included lower quality research (6465,6897).
Some clinical research has evaluated the effects of garlic when used in combination with antidiabetes drugs. Results show that taking a specific garlic powder product (Kwai, Lichtwer Pharmaceuticals) 300 mg three times daily, in combination with metformin, for 24 weeks reduces fasting blood glucose approximately 70% more than with metformin alone in patients with type 2 diabetes (51463).
There is insufficient reliable information available to determine if garlic significantly improves postprandial glucose levels or HbA1c (96004).
Hyperlipidemia. While conflicting results exist (731,732,4792,4793,4794,4795,4807,6897,15295,15296,51422,51429,51469,51590), the most reliable evidence shows that taking garlic may reduce total cholesterol and low-density lipoprotein (LDL) cholesterol levels in patients with hyperlipidemia (279,1873,1875,4782,4783,4784,4785,4786,4787,4788,4789,4795,6457,6897,51343,88399). However, any benefit is probably modest, and it may take more than 8 weeks before improvement is observed. Taking garlic doesn’t appear to significantly improve high-density lipoprotein (HDL) cholesterol or triglyceride levels.
The most recent and robust meta-analysis on this topic suggests that, on average, garlic preparations reduce total cholesterol by 15 mg/dL and LDL cholesterol by 6 mg/dL compared to placebo in patients with hyperlipidemia. These improvements appear to be more pronounced when garlic is taken for more than 8 weeks and in patients with total cholesterol and LDL cholesterol levels that are at least borderline high before treatment. This same analysis shows no reduction in triglycerides and only a slight increase in HDL of 1.5 mg/dL associated with garlic treatment (88399).
Whether garlic is beneficial for treating hyperlipidemia may also depend on the specific formulation or product taken. Mixed results have been reported for a variety of specific garlic products, including garlic powder tablets (Kwai, Lichtwer Pharma) (279,731,4782,4783,4784,4785,4787,4789,4792,4793)(4795,4807), aged garlic extract (Kyolic, Wakunaga) (1873,1875,15295), another garlic powder product (Garlicin, Nature’s Way) (15295), and others (732,51343). Subgroup analyses from the most robust meta-analysis to date suggest that products containing aged garlic extract may be more effective for lowering total cholesterol than garlic powder preparations. If garlic powder preparations are used, total cholesterol levels seem to be lowered to a greater degree in patients taking enteric-coated vs. non-enteric-coated garlic powder tablets. The opposite trend may be true for reducing LDL cholesterol. Garlic powder tablets seem to reduce LDL cholesterol levels while aged garlic extract does not. However, the few studies that did evaluate the effect of aged garlic extract on LDL cholesterol did so in patients with low LDL cholesterol levels at baseline. There is limited evidence on the use of raw garlic or garlic oil to support the use of these products over garlic powder or aged garlic extract for treating hyperlipidemia (88399).
Taking garlic with fish oil also appears to improve lipid parameters in some patients (4789,4790,51669). Garlic alone may be more effective than garlic plus fish oil for improving LDL cholesterol levels, but the combination may be useful in patients with elevated total cholesterol, LDL cholesterol, and triglycerides (4789).
Hypertension. Some clinical research shows that taking garlic orally can modestly reduce blood pressure in hypertensive and normotensive patients (277,278,279,1873,6897,16605,51442,51669,88398,88386). Analyses of clinical studies show that taking garlic can reduce systolic blood pressure by about 8% or about 5 mmHg and diastolic blood pressure by about 7% or about 3 mmHg in patients with or without hypertension (16605,51414,96007). When only patients with hypertension are considered, taking garlic can decrease systolic blood pressure by about 7-9 mmHg and diastolic blood pressure by about 4-6 mmHg. These results are limited by the fact that many of the included studies were only low to moderate quality and lasted only short-term (96007,96008,96014). Some garlic formulations evaluated for hypertension have included a specific garlic powder formulation (Kwai, Lichtwer Pharma) and a specific aged garlic extract (Garlic High Potency Everyday Formula 112, Wakunaga/Wagner) (1873,51442,88398).
Prostate cancer. The effect of dietary garlic on prostate cancer risk is inconsistent, but some evidence suggest benefit. Men in China who eat garlic 2.14 grams/day (about one clove) seem to have a 50% lower risk of developing prostate cancer (9876). Also, a pooled analysis of epidemiological research suggests that garlic consumption may be associated with a 23% decreased odds of developing prostate cancer (88410). However, other population research suggests that garlic consumption has no effect on prostate cancer risk in Iranian men (51454).
Preliminary clinical evidence suggests that taking garlic supplements might decrease the risk of developing prostate cancer (4777). There is also preliminary evidence that garlic extract might help improve prostate specific antigen, improve urinary flow, decrease urinary frequency, and reduce other symptoms associated with prostate cancer (10374).
Tick repellent. People consuming high doses of garlic (1200 mg daily) over an 8-week period seem to have a reduced number of tick bites when compared to placebo (3318). The effect of garlic compared to commercially available tick repellants is unknown (8027).
Tinea pedis. Applying a garlic gel containing 1% ajoene, a constituent of garlic, seems to be more effective than 0.6% ajoene gel, and seems to be as effective as 1% terbinafine (Lamisil) for tinea pedis infections. Sixty days after completing one week of treatment 1% ajoene produces 100% mycological cure, 0.6 % ajoene produces 72% mycological cure and 1% terbinafine produces 94% mycological cure (8019). Additional research suggests that 0.4% ajoene gel has a 7-day cure rate of around 80% for tinea pedis (4766).
Cystic fibrosis. Clinical research suggests that taking garlic oil macerate 625 mg daily for 8 weeks does not improve pulmonary function, symptom scores, or the need for antibiotic therapy compared to placebo in children with cystic fibrosis and chronic pulmonary infection (51438).
Familial hypercholesterolemia. In children with familial hyperlipidemia, taking garlic powdered extract, standardized based on alliin content, orally does not seem to significantly improve total serum cholesterol, low-density lipoprotein (LDL) or high-density lipoprotein (HDL) cholesterol levels, triglycerides, lipoprotein (a), apolipoprotein B-100, homocysteine, fibrinogen, or blood pressure (4796).
Gastric cancer. Despite some conflicting evidence (3320,4775,4776,51209,51460,96005), the most reliable research has found that garlic intake is not associated with a reduced risk of developing gastric cancer (14447,51470,97034,102016). A prospective, case-control study of 123,484 adults over a 30-year review period found that garlic intake, whether obtained from the diet or via supplementation, is not associated with a reduction in the rate of gastric cancer occurrence (97034). Clinical research evaluating the effects of taking aged garlic extract for 7 years also failed to show a reduced risk of developing gastric cancer up to 22 years later (14447,51470,102016), although there was a reduction in mortality associated with gastric cancer in subjects followed for 12-22 years (5-15 years after stopping the garlic extract) (102016). Meta-analyses and small population studies have suggested 23% to 51% lower odds of developing gastric cancer with increased dietary garlic intake compared to never eating garlic (3320,4775,4776,51209,51460,96005). However, these studies have limited external validity.
Helicobacter pylori. Taking garlic orally for H. pylori infection used to look promising due to laboratory and epidemiological evidence showing potential activity against H. pylori. However, when garlic cloves, powder, or oil is used in humans, it does not seem to have any beneficial effect for treating patients infected with H. pylori (3322,4761,4762,4763,4765,4774,97034).
Pre-eclampsia. Preliminary clinical evidence suggests that taking a specific garlic extract (Garlet, Cosar Pharmaceutical Company) 800 mg/day during the third trimester of pregnancy does not reduce the risk of developing pre-eclampsia in high-risk women or in women with first-time pregnancies (9201,51626).
INSUFFICIENT RELIABLE EVIDENCE to RATE
Alopecia areata. Preliminary clinical evidence suggests that applying garlic 5% gel, in addition to topical corticosteroid use, for 3 months increases hair growth by 18% compared to placebo plus corticosteroid in patients with alopecia areata (51386).
Angina. Preliminary clinical research suggests that garlicin 60 mg administered by intravenous drip daily for 10 days improves symptoms of angina by 7% compared to intravenous nitroglycerin in patients with unstable angina (51244).
Benign prostatic hyperplasia (BPH). Preliminary clinical research suggests that taking aqueous garlic extract 1 mg/kg daily for one month significantly decreases prostate mass and urinary frequency and significantly improves symptom scores and urinary flow rates compared to baseline in men with BPH (10374). A lack of adequate control limits the validity of these results.
Colorectal cancer. Several individual population studies have found that higher dietary intake of garlic is associated with a reduced risk of colorectal cancer (3320,4770,4771,4772). However, a meta-analysis of population research has found that higher intake of garlic from foods or supplements is not associated with a reduced risk of colorectal cancer (96003). Reasons for the discrepancy may relate to type of population study conducted. Most studies that show a preventative effect of garlic are case-control studies. These types of studies are prone to recall and selection bias, and some do not account for confounding factors associated with colorectal cancer (96003).
Few studies have examined any effects of garlic supplements. While a single study suggests that in patients with confirmed colorectal adenomas, taking high-dose aged garlic extract 2.4 mL daily for 12 months reduces the risk of developing new adenomas by 29% compared to taking a lower dose of 0.16 mL daily (51320), other studies do not support the use of garlic supplements for this purpose (4773,96003).
Corns. Preliminary evidence suggests that applying a specific lipid soluble garlic extract topically to corns on the feet twice daily results in significant corn improvement after 10-20 days of treatment (15030).
Coronary heart disease (CHD). Preliminary clinical research suggests that taking a specific garlic product (Allicor, INAT-Farma) 150 mg twice daily for 12 months can reduce the risk of sudden death and heart attack in patients with an elevated risk of developing coronary heart disease (51328). Other preliminary clinical research suggests that taking a specific aged garlic extract (Kyolic, Total Heart Health, Formula 108, Wakunaga) containing a standardized dose of 500 mg of aged garlic extract plus vitamin B12 200 mcg, folic acid 600 mcg, vitamin B6 25 mg, and L-arginine 200 mg daily for one year is associated with preventing further coronary artery calcification (51436).
Esophageal cancer. Preliminary population research regarding the use of garlic in preventing esophageal cancer is conflicting. Some evidence suggests that raw garlic consumption does not prevent the development of esophageal cancer (51508). However, other population research suggests that weekly garlic consumption decreases the risk of developing esophageal cancer (51209).
Exercise-induced muscle soreness. Preliminary clinical evidence suggests that taking allicin, a constituent of garlic, 80 mg daily for 14 days can reduce subjective assessments of exercise-induced muscle soreness in athletes (51404).
Fibrocystic breast disease. Preliminary clinical research suggests that taking a specific combination product (Karinat, INAT-Farma), containing garlic powder 150 mg, beta-carotene 2.5 mg, alpha-tocopherol 5 mg, and ascorbic acid 30 mg twice daily for 6 months reduces the severity of breast pain, premenstrual syndrome, and menstruation pain, and can cause regression of palpable symptoms of breast fibromatosis (51317). The effects of garlic alone cannot be determined due to the presence of other constituents included in this product.
Gastritis. Preliminary clinical research suggests that taking a specific combination product (Karinat, INAT-Farma), containing garlic 150 mg, beta-carotene 2.5 mg, alpha-tocopherol 5 mg, and ascorbic acid 30 mg twice daily for 6 months improves digestion, inhibits H. pylori infection, and reduces the risk of precancerous lesion formation in patients with gastritis (51308). The effects of garlic alone cannot be determined due to the presence of other constituents included in this product.
Hepatitis. Preliminary research suggests that taking 3-6 capsules of a product containing garlic oil 50 mg and diphenyl-dimethyl-dicarboxylate 25 mg per capsule daily for 6 weeks improves liver function biomarkers in patients with hepatitis (51478). The effects of garlic alone have not been determined.
Hepatopulmonary syndrome. Preliminary clinical research suggests that garlic oil 1-2 grams/m2 daily for 9-18 months may improve oxygen levels and remission rates in patients with hepatopulmonary syndrome (51439).
Lead toxicity. Preliminary clinical research suggests that taking garlic 400 mg three times daily for 4 weeks reduces blood lead concentration significantly from baseline, but it does not seem to significantly decrease lead concentration compared to D-penicillamine in patients with mild to moderate lead poisoning (51467).
Metabolic syndrome. Preliminary clinical research in adults with metabolic syndrome shows that taking raw, crushed garlic 100 mg/kg twice daily for 4 weeks increases high-density lipoprotein (HDL) cholesterol and decreases waist circumference, blood pressure, triglycerides, and fasting blood glucose when compared to baseline (98812). The validity of these findings is limited by the lack of a control group.
Obesity. Taking a specific product containing garlic and other ingredients in addition to diet and exercise might help reduce weight and body fat in obese patients compared to diet and exercise alone; however, it is unclear if this benefit is due to garlic, other ingredients, or the combination. Preliminary clinical evidence suggests that taking 1000 mg of a combination supplement (Prograde Metabolism) containing raspberry ketone (Razberi K, Integrity Nutraceuticals), caffeine, capsicum extract (Capsimax, OmniActive Health Technologies), garlic root extract, ginger root extract, bitter orange fruit (Advantra Z, Nutratech Inc), L-theanine, and black pepper fruit extract (Biperine, Sabinsa Corporation) twice daily for 8 weeks reduces body weight by 2.0%, fat mass by 7.8%, waist circumference by 2.0%, and hip circumference by 1.7% when used in combination with dieting and exercise compared to only 0.5%, 2.8%, 0.2%, and 0.4%, respectively, for patients who dieted and exercised alone (40802).
Oral mucositis. Preliminary clinical research suggests that using a garlic mouthwash 40 mg/mL three times daily for 4 weeks improves redness compared to baseline in patients with oral denture stomatitis (51466). Compared to nystatin, garlic has a lesser degree of recovery, but better patient satisfaction.
Oropharyngeal candidiasis. Preliminary clinical research suggests that applying a topical garlic paste four times daily for 14 days to affected areas can increase the rate of complete eradication of oral lesions by 23% compared to clotrimazole solution in patients with oral candidiasis (51330).
Osteoarthritis. Preliminary clinical research in overweight and obese women with osteoarthritis of the knee shows that taking garlic tablets (Nature Made) 500 mg twice daily for 12 weeks modestly reduces osteoarthritis-related pain scores by an additional 15% when compared with placebo (98813).
Vaginal candidiasis. Some preliminary clinical research suggests that application of a vaginal cream containing garlic and thyme nightly for 7 nights is as effective as clotrimazole vaginal cream for treating vaginal candidiasis (88387). However, other preliminary clinical research suggests that taking garlic (Garlicin, Nature’s Way) 1050 mg (3 tablets) twice daily for 14 days does not improve vaginal symptoms, candida colony counts, or cases of vaginal candidiasis in asymptomatic women with culture-positive candida infections (88405).
Warts. Preliminary evidence suggests that applying a specific lipid-soluble garlic extract topically to warts on the hands twice daily results in wart resolution within 1-2 weeks. An aqueous garlic extract also seems to provide modest improvement, but only after 30-40 days of treatment (15030).
More evidence is needed to rate garlic for these uses.
Dosing & Administration
Atherosclerosis: A standardized dehydrated garlic powder tablet (Kwai, Lichtwer Pharma) 300 mg, administered as a single dose or three times daily for up to 4 years, has been used (4798,51595). A specific time-released garlic supplement (Allicor, INAT-Farma) 150 mg twice daily for 24 months has been used (88394). Combination products containing garlic have also been used. A specific aged garlic extract supplement (Kyolic, Total Heart Health, Formula 108, Wakunaga) containing aged garlic extract 250 mg, vitamin B12 100 mcg, folic acid 300 mcg, vitamin B6 12.5 mg, and L-arginine 100 mg, taken daily for 12 months, has been used (88385). Also, a combination product containing aged garlic extract 300 mg/tablet and coenzyme Q10 30 mg/tablet, taken at a dose of four tablets daily for one year, has been used.
Athletic performance: A single dose of odor-modified dried garlic 900 mg prior to exercise has been used (51623).
Benign prostatic hyperplasia (BPH): Aqueous garlic extract 1 mg/kg daily for one month has been used. This extract was prepared from Kastamonu Garlic by incubating 2 kg of the garlic in 10 L of water for one month (10374).
Colorectal cancer: Capsules containing aged garlic extract 2.4 mL daily for 12 months have been used (51320).
Common cold: One capsule containing the garlic constituent allicin, taken daily for 12 weeks during the winter months, has been used (10787).
Coronary heart disease (CHD): One tablet of a specific garlic product (Allicor, INAT-FARMA) 150 mg twice daily for 12 months has been used (51328). A specific product containing aged garlic extract (Kyolic, Total Heart Health, Formula 108, Wakunaga) 500 mg plus vitamin B12 200 mcg, folic acid 600 mcg, vitamin B6 25 mg, and L-arginine 200 mg daily for one year has been used (51436).
Diabetes: Garlic powder 600-1500 mg daily in divided doses has been used for at least 12 weeks (96004). Specific garlic powder products (Allicor, INAT-Farma or Kwai, Lichtwer Pharma) 300 mg two to three times daily, in combination with metformin or an oral sulfonylurea, for 4-24 weeks has been used (51396,51463).
Exercise-induced muscle soreness: The garlic constituent allicin 80 mg daily for 14 days has been used (51404).
Fibrocystic breast disease: A specific product (Karinat, INAT-Farma) containing garlic powder 150 mg, beta-carotene 2.5 mg, alpha-tocopherol 5 mg, and ascorbic acid 30 mg twice daily for 6 months has been used (51317).
Gastritis: A specific product (Karinat, INAT-Farma) containing garlic powder 150 mg, beta-carotene 2.5 mg, alpha-tocopherol 5 mg, and ascorbic acid 30 mg twice daily for 6 months has been used (51308).
Hepatitis: 3-6 capsules of a product containing garlic oil 50 mg in combination with diphenyl-dimethyl-dicarboxylate 25 mg daily for 6 weeks has been used (51478).
Hepatopulmonary syndrome: Capsules containing garlic oil (Garlic Pearls, Ranbaxy, India) 1-2 grams/m2 daily, taken in two divided doses with meals for 9-18 months, have been used (51439).
Hyperlipidemia: A specific aged garlic extract (Kyolic, Wakunaga) 1000-7200 mg daily in divided doses for 4-6 months has been used (1873,1875). A specific standardized garlic powder tablet (Kwai, Lichtwer Pharma) 600-900 mg daily in two or more divided doses for 6-16 weeks has been used. This specific garlic product is standardized to contain 1.3% allicin (279,4782,4783,4784,4785,4787,4789). Another specific garlic powder product (Garlex, Bosch Pharmaceuticals) 300 mg twice daily for 12 weeks has been used (51343). Taking garlic powder 1200 mg plus fish oil 3 grams daily for 4 weeks has been used (4790). Taking garlic oil 500 mg plus fish oil 600 mg daily for 60 days has also been used (51669).
Hypertension: Garlic tablets 300-1500 mg in divided doses daily for 24 weeks has been used (88386). A specific standardized dehydrated garlic powder tablet (Kwai, Lichtwer Pharma) 2400 mg as a single dose or 600 mg daily for 12 weeks has been used (278,279). Capsules containing aged garlic extract 960 mg to 7.2 grams, taken daily in up to three divided doses for up to 6 months, have been used (1873,51442,88398). Specific products containing aged garlic extract include Kyolic (Garlic High Potency Everyday Formula 112, Wakunaga/Wagner) (51442). Garlic oil 500 mg plus fish oil 600 mg daily for 60 days has been used (51669).
Lead toxicity: Capsules containing dried powder garlic 400 mg three times daily for 4 weeks have been used (51467).
Metabolic syndrome: Raw, crushed garlic 100 mg/kg twice daily for 4 weeks has been used (98812).
Obesity: 1000 mg of a combination supplement (Prograde Metabolism) containing raspberry ketone (Razberi K, Integrity Nutraceuticals), caffeine, capsicum extract (Capsimax, OmniActive Health Technologies), garlic root extract, ginger root extract, bitter orange fruit (Advantra Z, Nutratech Inc), L-theanine, and black pepper fruit extract (Biperine, Sabinsa Corporation) twice daily for 8 weeks has been used (40802).
Osteoarthritis: A specific dried garlic product (Nature Made) 500 mg twice daily for 12 weeks has been used (98813).
Prostate cancer: Aqueous garlic extract 1 mg/kg daily for one month has been used. This extract was prepared from Kastamonu Garlic by incubating 2 kg of the garlic in 10 L of water for one month (10374).
Tick repellent: Capsules containing garlic 1200 mg daily for 8 weeks has been used (3318).
Alopecia areata: Application of 5% garlic gel four times daily for 3 months has been used (51386).
Corns: Applying a specific lipid soluble garlic extract topically to corns on the feet twice daily for 10-20 days has been used (15030).
Oral mucositis: A garlic mouthwash 40 mg/mL three times daily for 4 weeks has been used (51466).
Oropharyngeal candidiasis: Garlic paste applied four times daily for 14 days has been used (51330).
Tinea corporis: Garlic gel containing 0.6% ajoene, a constituent of garlic, has been applied twice daily for 7 days (4767).
Tinea cruris: Garlic gel containing 0.6% ajoene, a constituent of garlic, has been applied twice daily for one week (4767).
Tinea pedis: Application of a topical cream containing 0.4% ajoene, a constituent of garlic, twice daily for 7-14 days has been used (4766). Application of a topical garlic gel containing 0.6% or 1.0% ajoene twice daily for 7 days has also been used (8019).
Vaginal candidiasis: Application of a vaginal cream containing garlic and thyme (concentrations unknown) nightly for 7 nights has been used (88387).
Warts: Lipid-soluble garlic extract, applied twice daily for 1-2 weeks, has been used. Also, aqueous garlic extract applied twice daily for 30-40 days has also been used (15030).
Angina: Garlicin 60 mg, administered by intravenous drip daily for 10 days, has been used (51244).
Standardization & Formulation
Many garlic products, including garlic powder, garlic oil, and garlic extract, are standardized to allicin content. Tablets containing enteric-coated Australian garlic powder have been standardized to provide 2.4 mg allicin per 220 mg garlic powder (51250). A specific garlic powder tablet (Garlet) has been standardized to contain allicin 1000-1200 mcg per 400 mg of dried powder garlic (9201,51467). Some specific garlic powder products, including Kwai (Lichtwer Pharma) and Garlex (Bosch Pharmaceuticals), have been standardized to contain 1.3% allicin (731,4782,4786,4788,4789,4795,4796,4798,6457,6897)(51343,51590,51598).
Garlic oil has also been standardized to allicin content. In clinical research, garlic oil 275 mg was standardized to contain 800 mcg allicin (4763). A specific product containing steam-distilled garlic oil (Tegra, Hermes Arzneimittel GmbH) 5 mg (equivalent to 4-5 grams of fresh garlic cloves) has been standardized to contain 4000 units of allicin (732).
Some garlic extract products have also been standardized to allicin content. Tablets containing enteric-coated Thai garlic extract have been standardized to contain 1.12% allicin (15296). Other garlic extract products, particularly aged garlic extract, have been standardized to S-allyl cysteine content. A specific product containing aged garlic extract (Kyolic, Garlic High Potency Everyday Formula 112, Wakunaga/Wagner) 240 mg (equivalent to 625 mg of fresh garlic) has been standardized to contain 0.6 mg of S-allyl cysteine (51442,88398).
General: Common side effects of oral and intravenous garlic include malodorous breath, body odor, nausea, vomiting, flatulence, weight loss, facial flushing, tachycardia, dizziness, insomnia, and allergic reactions (732,1873,42692,51316,51462,88398,88405). One potential reaction of concern associated with oral garlic is increased risk of bleeding (586,587,4366,4801,4802,51228,51295,51397,51491,51500)(51532,51534,51578,51593,51594).
Topically, fresh garlic may cause elicit dermatitis (4833,12635,51210,51215,51258,51265,51292,51375,51403,51406)(51412,51483,51498,51510,51511,51512,51519,51530,51560,51617)(51618,51628) or burns in children and infants (585,51226,51495,51536,51576), as well as in adults (4832,51230,51252,51281,51377,51418,51558,51577,88409,96006).
Oral ingestion of a large amount of garlic has been associated with an acute myocardial infarction in a 23 year-old man with no known history of cardiac disease or known risk factors (89462).
Topically, garlic may cause contact dermatitis and urticaria (4833,5004,12635,51258,51265,51375,51403,51412,51459,51511)(51512,51530,51616,51617,51618), as well as contact cheilitis (51384). Fresh garlic may be more likely to elicit a reaction than garlic extract. Most reactions have resolved following withdrawal of garlic therapy. In one case report, applying crushed garlic on the neck to help ease a sore throat resulted in an itchy, burning, erythematous lesion in a young female patient. The lesion healed after one week of treatment with topical antibiotics, steroids, and antihistamine ointments (88390). Cases of occupational eczema or dermatitis have been reported in cooks (51303), food handlers (51292), and caterers (51304). According to one case report, dermatitis appeared in chefs exposed to garlic (15033). Treatment with acitretin 25 mg daily or topical psoralen-ultraviolet A (PUVA) for 12 weeks proved effective in mitigating the symptoms. Topically, garlic may also cause chemical burns, usually within 12 hours of application. Second- and third-degree chemical burns have been reported in adults, children, and infants exposed to topical garlic, often as an unintended consequence of using garlic medicinally on the skin (585,4832,51226,51230,51252,51281,51377,51418,51495,51536)(51558,51576,51577,88409,96006). A case of painful blisters on the soles of the feet of a 23 year-old Chinese woman has been attributed to chemical burns caused by applying crushed raw garlic for 3 hours (51440). Topically, garlic may also cause hyperpigmentation, ulcers, necrotic lesions, facial flushing, and local irritation (4832,15030,51268,51269).
Orally, garlic has been associated with a case of superficial pemphigus in a 49 year-old man with type 2 diabetes (51564). Garlic-induced iatrogenic burns have also been reported (51468). Oral ulcers have been reported in humans (51467). Oral intake of a specific garlic product containing allicin (Allimax) has been associated with a case of pruritic rash (51474). Enteric-coated garlic tablets standardized to 1.5% allicin have also been associated with a case of pruritus (51316).
One poor-quality study that was designed to measure platelet aggregation noted a small, significant reduction in mean blood glucose levels in patients treated with 800 mg of dehydrated garlic (Kwai) daily, from 89 mg/dL to 79 mg/dL over four weeks (51443). However, multiple other clinical trials have not demonstrate significant effects of oral garlic preparations on measures of glycemic control in diabetic or nondiabetic patients, when measured either as primary outcomes or secondary outcomes (279,4783,4794,4798,51493,51528,51594,51605)(51606,51607).
Orally, dehydrated garlic preparations or raw garlic may cause malodorous breath (51438,51444), body odor (732,1873,4784,4793,4795,4798,9201,10787,42692,49769)(51269,51316,51467,51602), abdominal pain or fullness, anorexia, diarrhea, constipation, flatulence, belching, taste sensations, heartburn, nausea, unpleasant taste, reflux, and bowel obstruction (6457,6897,9201,49769,51269,51343,51380,51438,51442,51450)(51457,51466,51471,51474,51520,51593,51602,51623,88398,88405). In a case report of eosinophilic gastroenteritis, garlic was suggested as the possible causative allergen. The patient was a 42 year-old woman who presented with symptoms including pollinosis, asthma, diarrhea, heart burn, peripheral eosinophilia, and urticaria. After stopping use of garlic and sesame, the patient improved (51441). In a case report of eosinophilic esophagitis, garlic was determined to be the causative agent in a patient with long-standing gastrointestinal symptoms. The patient had attempted to treat his upper gastrointestinal symptoms as gastrointestinal reflux disease without success for many years. Skin prick testing showed a positive reaction to garlic, of which the patient noted frequent consumption. Marked symptom improvement was noted within 3 weeks of garlic avoidance (88393). In another case report, a patient taking garlic for hypertension reported odynophagia and retrosternal pain after taking garlic without any water the previous day. An esophageal lesion 3 cm in length was detected upon endoscopy. The symptoms resolved 3 days after starting a liquid diet and taking lansoprazole 30 mg twice daily and sucralfate four times daily (88389). One case of bowel obstruction was reported in a 66 year-old man who ingested an entire garlic bulb (51525).
Intravenously, garlic 1 mg/kg of body weight daily diluted into 500 mL saline and administered over four hour has reported caused abdominal discomfort, vomiting, diarrhea, nausea, anorexia, flatulence, weight loss, and garlicky body odor (51462).
Garlic’s effect on platelet function is well known, and can possibly increase the risk of bleeding. Oral use of dietary garlic or supplements containing garlic has caused platelet dysfunction, increased fibrinolytic activity, prolonged bleeding time, retrobulbar hemorrhage (bleeding behind the eye) postoperative bleeding, and spinal epidural hematoma (586,587,4801,4802,11325,51397,51473,51491,51532,51534)(51570,51584,51593,51594). Also, a case of kidney hematoma following extracorporeal shock-wave lithotripsy (SWL) has been reported for a nephrolithiasis patient taking aged garlic (51630). Also a case of increased bleeding time that complicated epistaxis management has been reported for a patient taking garlic, aspirin, and milk thistle (51426).
Intravenously, garlic has been associated with the development of thrombophlebitis at the injection site (51462).
Dizziness, insomnia, headaches, diaphoresis, fever, chills, somnolence, increased appetite, euphoria, and weight loss have been reported with garlic (15032,42692,51316,51467,51471,51520). In one case, the smell of garlic was identified as a trigger for migraines in a 32-year-old female. The subject reported fortification spectra along with visual spots for a few seconds followed by instantaneous biparietal, crushing level (10/10) headaches upon exposure to the scent of garlic or onion (88404).
Garlic exposure, most notably in occupational settings, may cause asthma and other symptoms such as sneezing, nasal obstruction, rhinorrhea, and sinusitis (40661,51218). A case of minor hemoptysis has been reported for one patient with cystic fibrosis following intake of a garlic capsules orally once daily for 8 weeks (51438). A 77 year-old woman developed pneumonia related to the intake of one whole black garlic clove daily. The cloves were prepared by heating a whole garlic bulb in a pot for one month. Symptoms included dyspnea and coughing and test results were positive for lymphocyte-induced stimulation by black garlic and raw garlic. She required treatment with oral steroids and was told to avoid garlic (96011).
There is a case report of an immediate sensitivity reaction to raw garlic, resulting in wheals, in a 31-year old woman. She did not react to cooked garlic, and skin prick tests showed allergy only to raw garlic. She reacted to a specific protein (96015). Researchers note that at least some allergens in raw garlic are heat labile (88392,96012,96015). This suggests that consuming cooked rather than raw garlic may help avoid this reaction in patients allergic to raw garlic. However, different people react to different allergens in garlic. At least some of these allergens are heat stable (96012). While rare, garlic-induced anaphylaxis has been reported (88392,96012).
Toxicity studies have been limited. In mice, the LD50 of allicin, a garlic constituent, has been reported as 120 mg/kg subcutaneously and 60 mg/kg intravenously (51627). The LD50 for garlic extract has been reported as >30 mL/kg intraperitoneally (51517). Orally, doses up to 2000 mg/kg five times per week have been tolerated by rats for up to 6 months (51518).
Interactions with Drugs
Raw garlic and a variety of garlic extracts have antiplatelet activity and can increase prothrombin time (586,616,1874,3234,4366,4802,4803,51397,96013). Theoretically, garlic might enhance the effects and adverse effects of other anticoagulant and antiplatelet drugs, including aspirin, clopidogrel (Plavix), enoxaparin (Lovenox), warfarin (Coumadin), and others.
Evidence from human research suggests that garlic and garlic extract lowers blood glucose levels in healthy and diabetic individuals (51463,96004). Theoretically, concomitant use of garlic and antidiabetes drugs might increase the risk of hypoglycemia. Dose adjustments might be necessary. Some antidiabetes drugs include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), and others.
Garlic and garlic extracts have blood pressure-lowering effects (277,278,279,1873,4787,6897,16605,51414,51442,51669)(88386,88398,96007). Theoretically, combining garlic with other blood pressure agents might cause additive hypotensive effects; use with caution. Some antihypertensive drugs include nifedipine (Adalat, Procardia), verapamil (Calan, Isoptin, Verelan), diltiazem (Cardizem), isradipine (DynaCirc), felodipine (Plendil), amlodipine (Norvasc), and others
In one case, an HIV positive patient consuming six stir-fried garlic cloves three times weekly developed suboptimal atazanavir levels and increases in HIV viral load. While the exact cause of this interaction is unclear, there is speculation that garlic might decrease the intestinal absorption of atazanavir or increase its metabolism by inducing cytochrome P450 3A4 (CYP3A4) (88388). Until more is known, advise patients not to consume large amounts of garlic while taking atazanavir.
Clinical research suggests garlic oil can inhibit the activity of CYP2E1 by 39% (10847). Use garlic oil cautiously in patients taking drugs metabolized by these enzymes. Some drugs metabolized by CYP2E1 include acetaminophen, chlorzoxazone (Parafon Forte), ethanol, theophylline, and anesthetics such as enflurane (Ethrane), halothane (Fluothane), isoflurane (Forane), methoxyflurane (Penthrane).
There is concern that garlic can induce intestinal cytochrome P450 3A4 (CYP3A4) and significantly reduce levels of drugs metabolized by this enzyme. This is primarily based on a pharmacokinetic study showing that taking a specific garlic product (GarliPure Maximum Allicin Formula, Natrol Inc.) twice daily, providing a total of 9.28 mg allicin, along with saquinavir 1200 mg for 3 days, significantly reduces saquinavir levels. The area under the curve of saquinavir was reduced by 50% and maximum concentration was reduced by 47% (7027,93578). Researchers speculate that the allicin constituent in garlic induces CYP3A4 in the gut mucosa and is responsible for the reduced levels of saquinavir (7027). Another study shows that giving docetaxel intravenously, bypassing the CYP3A4 enzymes in the gut mucosa, along with the same specific garlic product for 12 consecutive days, does not significantly affect the pharmacokinetics of docetaxel (17221).
There is also concern that garlic may inhibit hepatic CYP3A4. In one case report, a patient given tacrolimus following a liver transplant experienced increase tacrolimus levels, elevated liver function tests, and liver injury after taking a specific garlic supplement (Garlicin Cardio, Nature’s Way) at up to three times the manufacturer recommended dose for 7 days. It is speculated that garlic inhibited hepatic CYP3A4, which increased levels of tacrolimus in blood and caused this effect (96010).
Several other pharmacokinetic studies have evaluated the impact of other garlic formulations and have found no effect on CYP3A4 substrates. Most of the products in these studies provided little or no allicin. In one study, a garlic product with undetectable allicin levels (Natural Source Odorless Garlic, Life Brand) did not have an effect on ritonavir, a CYP3A4 substrate (94506). In other studies, garlic products without significant allicin content, such as garlic oil and extracts containing alliin and alliinase, also do not affect CYP3A4 (10335,10847,15031).
Until more is known about this potential interaction, use garlic containing allicin cautiously in patients taking drugs that are metabolized by CYP3A4. Drugs that might be affected include some calcium channel blockers (diltiazem, nicardipine, verapamil), chemotherapeutic agents (etoposide, paclitaxel, vinblastine, vincristine, vindesine), antifungals (ketoconazole, itraconazole), glucocorticoids, alfentanil (Alfenta), cisapride (Propulsid), fentanyl (Sublimaze), lidocaine (Xylocaine), losartan (Cozaar), fexofenadine (Allegra), midazolam (Versed), and others.
Research in animal models suggests that an aqueous extract of garlic can reduce isoniazid levels by about 65%. Garlic reduces both maximum concentration (Cmax) and area under the curve (AUC), but does not seem to affect half-life. This suggests that garlic extract might inhibit isoniazid absorption across the intestinal mucosa (15031); however, the exact mechanism of this potential interaction is not known.
Protease inhibitors are metabolized by cytochrome P450 3A4 (CYP3A4) isoenzymes. There is some concern that some garlic products induce CYP3A4 and can potentially cause subtherapeutic levels of protease inhibitors. This is primarily based on a pharmacokinetic study showing that taking a specific garlic product (GarliPure Maximum Allicin Formula, Natrol Inc.) twice daily, providing a total of 9.28 mg allicin, along with saquinavir 1200 mg for 3 days, significantly reduces saquinavir levels. The area under the curve of saquinavir was reduced by 50% and maximum concentration was reduced by 47% (7027,93578). Researchers speculate that the allicin constituent in garlic induces CYP3A4 in the gut mucosa and is responsible for the reduced levels of saquinavir (7027). Another study shows that bypassing the CYP3A4 enzymes in the gut mucosa, by giving a CYP3A4 substrate intravenously with the same specific garlic product, does not significantly affect the substrate’s pharmacokinetics (17221). Several pharmacokinetic studies have evaluated the impact of other garlic formulations on CYP3A4 substrates and have found no effect. Most of the products in these studies provided little or no allicin (10335,10847,15031,94506).
Until more is known advise patients not to use garlic products containing allicin with protease inhibitors. Some protease inhibitors include amprenavir (Agenerase), nelfinavir (Viracept), ritonavir (Norvir), and saquinavir (Fortovase, Invirase).
Saquinavir is a substrate of cytochrome P450 3A4 (CYP3A4) isoenzymes. There is some concern that garlic induces CYP3A4 and can potentially cause subtherapeutic levels of saquinavir. This is primarily based on a pharmacokinetic study showing that taking a specific garlic product (GarliPure Maximum Allicin Formula, Natrol Inc.) twice daily, providing a total of 9.28 mg allicin, along with saquinavir 1200 mg for 3 days, significantly reduces saquinavir levels. The area under the curve of saquinavir was reduced by 50% and maximum concentration was reduced by 47% (7027,93578). Researchers speculate that the allicin constituent in garlic induces CYP3A4 in the gut mucosa and is responsible for the reduced levels of saquinavir (7027). Several pharmacokinetic studies have evaluated the impact of other garlic formulations on CYP3A4 substrates and have found no effect. Most of the products in these studies provided little or no allicin (10335,10847,15031,94506).
Until more is known about this potential interaction, patients taking saquinavir should avoid or use garlic with caution.
In one case report, a patient given tacrolimus following a liver transplant experienced increase tacrolimus levels, elevated liver function tests, and liver injury after taking a specific garlic supplement (Garlicin Cardio, Nature’s Way) at up to three times the manufacturer recommended dose for 7 days. It is speculated that garlic inhibited hepatic CYP3A4, which increased levels of tacrolimus in blood and caused this effect (96010).
Raw garlic and a variety of garlic extracts have antiplatelet activity and can increase prothrombin time (586,616,1874,3234,4366,4802,4803,51397). There is concern that taking garlic with warfarin might increase the international normalized ratio (INR) and the risk of bleeding. There is a report of two patients who experienced an increase in a previously stabilized internationalized ratio (INR) with concomitant oral garlic and warfarin use (51228,51631). However, this report has been subsequently debated due to limited provided clinical information. Other preliminary clinical research suggests that patients stabilized on warfarin who take a specific aged garlic extract (Kyolic, Wakunaga Pharmaceutical Co.), 1.525 grams twice daily for 12 weeks, do not seem to have a significantly increased INR or increased risk of bleeding events (15032). Use of 2 grams of garlic twice daily for 2 weeks also does not seem to affect the pharmacokinetics of a single 25 mg dose of warfarin in healthy men (16416). More evidence is needed to determine the safety of using garlic along with warfarin. Patients on warfarin should avoid or use garlic cautiously. Warfarin dose adjustments might be necessary.
Interactions with Herbs & Supplements
ANTICOAGULANT/ANTIPLATELET HERBS AND SUPPLEMENTS: Raw garlic and a variety of garlic extracts have antiplatelet activity and can increase prothrombin time (586,616,1874,3234,4366,4802,4803,51397,96013). 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.
HERBS AND SUPPLEMENTS WITH HYPOGLYCEMIC POTENTIAL: Garlic and garlic extract can lower blood glucose levels (96004). Theoretically, garlic might have additive effects with other herbs and supplements that decrease blood glucose levels. Some herbs and supplements with hypoglycemic potential include agaricus mushroom, devil’s claw, fenugreek, guar gum, Panax ginseng, Siberian ginseng, and others.
HERBS AND SUPPLEMENTS WITH HYPOTENSIVE EFFECTS: Garlic and garlic extracts have blood pressure lowering effects (277,278,279,1873,4787,6897,16605,51414,51442,51669)(88386,88398). Theoretically, combining garlic with other herbs or supplements with hypotensive effects might increase the risk of hypotension. Some of these herbs and supplements include andrographis, casein peptides, cat’s claw, coenzyme Q-10, fish oil, L-arginine, lycium, stinging nettle, theanine, and others.
Interactions with Foods
Interactions with Lab Tests
INTERNATIONAL NORMALIZED RATIO (INR), PROTHROMBIN TIME (PT): Garlic can increase INR in patients anticoagulated with warfarin (Coumadin). There are two case reports of increased INR associated with concomitant use of garlic products and warfarin (616).
Interactions with Diseases
DIABETES: Garlic might lower blood glucose levels (96004). Theoretically, use of garlic might increase the risk of blood sugar levels becoming too low in patients with diabetes. Monitor blood glucose levels closely.
HYPOTENSION: Garlic can lower blood pressure (277,278,279,1873,4787,6897,16605,51414,51442,51669,88386,88398). Theoretically, garlic might increase the risk of blood pressure becoming too low in patients with hypotension
SURGERY: Garlic might prolong bleeding time and may interfere with blood pressure control during surgery. Garlic should be discontinued one to two weeks prior to scheduled surgery (277,278,279,587,1873,4787,4800,6897,11325,16605)(51414,51442,51669,88386,88398). Also, garlic might affect blood glucose levels (96004). Theoretically, garlic might interfere with blood glucose control during and after surgical procedures. At least one case report suggests that consuming approximately 4 grams crushed garlic with each meal for a few weeks, and 12 grams garlic powder the evening before surgery, increased prothrombin time and prolonged bleeding (96013). Tell patients to discontinue garlic at least 2 weeks before elective surgical procedures.
Mechanism of Action
General: The applicable part of garlic is the bulb. The bulb of garlic contains the cysteine sulfoxide Many of the pharmacological effects of garlic are attributed to the allicin, ajoene, and other alliin, also known as S-allyl-L-cysteine sulfoxide (8017). When the garlic bulb is crushed, ground, or cut, the alliin constituent is converted to allicin (also known as diallylthiosulfinate) by the enzyme alliinase (3251,4768,8017). Fresh garlic contains approximately 1% alliin. One milligram of alliin is converted to 0.458 mg allicin (4800). 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 alliinase. Freeze-dried garlic may contain little or no allicin. The age of garlic affects the amount of alliin contained in the product. 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 (4800).
Other garlic constituents include S-propylcysteinesulfoxide (PCSO) and S-methylcysteine-sulfoxide (MCSO), which can also be converted by alliinase to constituents such as allyl methane thiosulfinate, methyl methanethiosulfinate, and other thiosulfinates. Volatile constituents of garlic include diallyldisulfide (DADS), dimethyltrisulfide (DATS), and sulfur dioxide (8017).
Garlic extracts have been shown to contain constituents such as E-ajoene (8017). Aged garlic extracts may contain constituents such as S-allylcysteine (SAC) and S- allylmercaptocysteine (SAMC), while garlic oil may include constituents such as diallyldisulfide and dimethyltrisulfide (3234,8017). Heat and steam distillation used to produce garlic oil from crushed garlic converts allicin to allyl sulfides which are thought to have biological activity (3251).
To improve effectiveness, garlic preparations may be enteric coated to protect the active constituents from degeneration by stomach acid (9203).
Anthelmintic effects: Evidence from animal research suggests that minced garlic or aqueous extract of garlic can reduce Capillaria infestation in common carp (Cyprinus carpio) (51492). The exact mechanism is unclear, and it is not clear if these effects are observable in humans.
Antibacterial effects: Fresh garlic has shown activity against Escherichia coli, methicillin-resistant Staphylococcus aureus, and Salmonella enteritidis; it has been suggested as a food additive to prevent food poisoning (4808). In addition to fresh garlic, crude garlic extract has also been shown to have antimicrobial activity against Streptococcus mutans, suggesting it may be beneficial for eliminating bacterial in the mouth known to cause dental caries (51391,51400). Other in vitro research suggests that garlic extract may have antibacterial activity against several strains of mycobacteria, including Mycobacterium tuberculosis, Mycobacterium avium-intracellulare, and Mycobacterium kansasii, three bacteria associated with pulmonary infections (51490,51506,51544,51582). However, garlic extract does not seem to have additive effects when used in combination with antituberculosis drugs (51490). Garlic oil has also been shown to have antimicrobial activity against Mycobacterium tuberculosis (51582). The antibacterial activity of garlic oil has been attributed to its allyl sulfur compounds (51434). It has been suggested that garlic oil’s antimicrobial activity is more potent than garlic powder on a unit weight basis (51227).
The antimicrobial effects of garlic have been attributed to its allicin content. Allicin is believed to inhibit RNA synthesis and reduce DNA and protein synthesis (51484). Allicin and other sulfur-containing constituents of garlic may also inhibit bacterial growth by interacting with and inactivating enzymes necessary for growth (51489). The garlic constituent ajoene also possesses antibacterial activity against both Gram-positive and -negative bacterial species in vitro. The disulfide bond in ajoene may be responsible for these effects, but the exact mechanism of action is unclear (51567).
Antidiabetic effects: Garlic seems to lower blood glucose in people with or without diabetes (96004). Preliminary clinical research suggests some compounds in garlic, such as S-methylcysteine sulfoxide and S-allylcysteine sulfoxide, might have some antidiabetic activity (9875). In vitro evidence suggests that S-allyl cysteine sulfoxide stimulate insulin secretion from beta-cells (51557). Other in vitro evidence suggests that aged garlic extract can inhibit the formation of advanced glycation end products, which are associated with diabetic complication (51387).
Antifungal effects: The garlic constituents allicin and ajoene are thought to be responsible for garlic’s antifungal activity against tinea infections (8017,8019). Aged garlic extract and its constituents ajoene and allitriduim have shown antifungal activity against Scedosporium prolificans, a fungal species that can affect immunocompromised patients (51273). Fresh garlic, aged garlic extract, and the garlic constituent allicin have shown antifungal activity against Candida albicans in the laboratory (4808,51456,51489). In humans, oral intake of garlic extract 25 mL was associated with anticandidal activity in serum for up to 1 hour after ingestion (51522). The antifungal activity of garlic against candida infections has been attributed to the ability of allicin to downregulate SIR2, a gene involved in with the formation of hyphae (51475). Garlic may also inhibit the synthesis of lipids by Candida albicans, resulting in cell leakage (51489,51501).
Antilipemic effects: Various clinical studies have shown that garlic can improve levels of total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides in patients with hyperlipidemia (51463,51465). There is some evidence various garlic constituents may be potent inhibitors of hepatic cholesterol synthesis (8407,51216,51246,51649). In patients with hyperlipidemia, garlic might lower cholesterol levels by acting as a HMG-CoA reductase inhibitor (statin) (4810,4811,51646,51647,51648). Garlic may also reduce the activity of enzymes involved in cholesterol synthesis, including hepatic glucose-6-phosphate dehydrogenase, malic enzyme, and squalene monooxygenase (51246,51645), as well as enzymes that catalyze fatty acid synthesis such as fatty acid synthetase (51646). However, some laboratory evidence suggests that garlic might also inhibit or reduce the activity of cholesterol 7 alpha-hydroxylase, an enzyme involved in the conversion of cholesterol to bile acids (51646,51647).
Antioxidant effects: In various laboratory studies, garlic and its constituents displayed antioxidant activity, including increasing that activities of glutathione peroxidase, catalase, and superoxide dismutase; lowering xanthine oxidase activity; and inhibiting lipid peroxidation and prostaglandin production (51207,51241,51256,51268,51270,51287,51298,51309,51311,51325)(51337,51342,51348,51362,51363,51381,51407,51410,51423,51433)(51575,51592,51637,51638). Some laboratory evidence suggests that the antioxidant capacity of fresh garlic may be greater than that of dried garlic (40694). However, in humans, supplementation with garlic as well as other dietary antioxidants lacked an effect on serum antioxidant capacity or plasma F2-isoprostanes (51383).
Antiparasitic effects: Laboratory evidence suggests that garlic oil has broad-spectrum activity against Trypanosoma, Plasmodium, Giardia, Leishmania, and Cochlospermum planchonii (51335,96007). Animal research suggests that the garlic constituent allicin decreases infections and increases survival of mice exposed to Plasmodium, the parasitic protozoa that causes malaria (51368). In animals and in vitro, garlic extract augments Leishmania engulfment and destroys amastigotes by macrophages (51340,51399). In vitro, the garlic constituent ajoene inhibits enzymes found in Trypanosoma (51589).
Antiviral effects: Preliminary in vitro evidence suggests that garlic compounds, including ajoene, allicin, allyl methyl thiosulfinate, and methyl allyl thiosulfinate, might have activity against viruses such as cytomegalovirus, influenza B, herpes simplex virus type 1, herpes simplex virus type 2, parainfluenza virus type 3, vaccinia virus, vesicular stomatitis virus, and human rhinovirus type 2 (4769,51488,51547,51591,96007).
Athletic performance effects: A single administration of garlic increased endurance performance, likely due to increase in fibrinolytic activity in the resting state (51623).
Cardiovascular effects: Human research shows that high-dose garlic powder for up to 4 years reduces arteriosclerotic and age-dependent plaque volume in both carotid and femoral arteries (4798). 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 (1871,1876,1880,4813,8017,8408,51264,51545,51650). There is evidence that LDL oxidation may be inhibited by the organosulfur constituents of garlic, including S-allyl cysteine, S-allyl mercaptocysteine, alliin, allixin, N-acetyl-S-allyl cysteine, and diallyl disulfide (DADS) (8408,51583). However, this hypothesis has been in dispute based on a six-month trial in moderately hypercholesterolemic volunteers, which failed to demonstrate any effects of garlic supplementation on lipoprotein oxidation (51211). Also, garlic does not seem to reduce levels of lipoprotein (a), a lipoprotein similar to LDL, in human plasma (96009).
In addition to inhibiting LDL oxidation, laboratory research suggests that garlic constituents, including diallyl sulfide (DAS) and diallyl trisulfide (DATS), suppress oxidized LDL-induced expression of E-selectin and vascular cell adhesion molecule (VCAM)-1, thereby decreasing monocyte adhesion to endothelial cells which occurs at early stages of atherosclerosis (51409). Aged garlic extract does not appear to affect the expression of adhesion molecules nor the adherence of leukocytes on the surface of endothelium, although it does appear to reduce the development of fatty streak formation and cholesterol accumulation in the vessel wall of animals fed high cholesterol diets, suggesting an alternative method for protection against the onset of atherosclerosis (1879,51234). Similarly, in vitro and ex vivo evidence suggests that garlic powder extract may reduce lipid accumulation in atherosclerotic human aortic cells by inhibiting acyl-CoA:cholesterol acyltransferase activity and stimulating cholesteryl ester hydrolase (51535,51651). Some evidence in humans suggests that garlic inhibits inflammatory compounds, including C-reactive protein (CRP) and inflammatory cytokines. An increased level of these compounds is associated with an increased risk of cardiovascular disease (96007).
Chemoprotective/antitumor effects: There is preliminary evidence that suggests garlic and aged garlic extract may have pharmacological effects that are similar to Bacillus Calmette-Guerin (BCG) vaccine in the treatment of bladder cancer (8018). Garlic also seems to have humoral and cellular immunostimulant activity. There is evidence garlic and aged garlic extract might stimulate T-cell proliferation; restore suppressed antibody responses; stimulate macrophage cytotoxicity and phagocytosis of tumor cells; and induce the release of interleukin-2 (IL-2), tumor necrosis factor-alpha (TNF-alpha), and gamma interferon (8018). The constituents in garlic S-allyl cysteine and S-allyl mercaptocysteine have been shown to have radical scavenging activity. S-allyl mercaptocysteine has also been shown to have activity against erythroleukemic cancer cells, breast cancer cells, and prostate cancer cells (1871,1877,1878,1879,1880,1881,1882). The constituent ajoene has been observed to induce apoptosis in human leukemia cells (8017). Laboratory evidence suggests garlic may induce detoxifying enzymes such as glutathione-S-transferase to remove harmful electrophiles from carcinogens (8017). Additionally, garlic might enhance selenium absorption and protect against tumorigenesis (4815).
In human research, aged garlic extract suppressed both the size and number of colon adenomas in patients (51359). Animal studies have reported protective effects of garlic against hepatotoxins (51247,51286,51502,51555) and chemotherapy-induced toxicity from cyclophosphamide (51338,51413,51480), doxorubicin (51220,51296,51433), methylcholanthrene (51479), gentamicin (51224), 4-nitroquinoline 1-oxide (51248), methotrexate (51365), and bromobenzene (1883,51586). There is some evidence that the chemical constituents containing allyl groups may be responsible for chemoprotective properties (51496). The chemopreventive potential of garlic may be due to its antioxidant activity and modulation of lipid peroxidation (51408,51575,51637,51638,51654). Compounds in garlic have been found to modulate the activity of xenobiotic-metabolizing enzymes that activate or detoxify carcinogens, in animal research (51326). Garlic has demonstrated strong inhibition of cancer development in the presence of known tumor promoters, including 12-O-tetradecanoylpharbol-13-acetate (51302,51485), 7,12-dimethylbenzanthracene (51280), and phorbol-myristate-acetate (51523), as well as tumor inducers such as 7,12-dimethylbenzanthracene (51302) and 1,2-dimethylhydrazine (51504,51566).
Research has provided evidence of the antiproliferative effects of garlic on human cancer cell lines (51237,51251), including induction of apoptosis (51259,51262,51267,51277,51291,51379,51405,51415,51581,51655), regulation of cell cycle progression (51260), and signal transduction modification. Both cellular proliferation (51238,51405,51548,51656) and immune function appear to be affected (51235,51657). Allicin, the major constituent of garlic, plays a key role in the antiproliferative effects and causes depletion in intracellular glutathione (GSH) levels (51251). In animal research evaluating the effects on tumor marker enzymes, garlic elevated the activity of gamma-glutamate transpeptidase (GGT), glutathione S-transferase (GST), 5′-nucleotidase, alkaline phosphatase (ALP), aspartate transaminase (AST), and alanine transaminase (ALT), and reduced the activity of glucose 6-phosphatase (G6Pase) (51640).
An aqueous extract of garlic administered orally to hamsters resulted in inhibition of buccal pouch carcinogenesis and restoration of normal cytokeratin expression (51257). This effect may have been due to regulatory effects on differentiation, tumor invasiveness, and migratory and metastatic potential; the mechanism may be garlic’s influence on tumor inhibition (51257). Other potential chemopreventive mechanisms of garlic include modulation in activity of several metabolizing enzymes that activate and detoxify carcinogens and inhibit DNA adduct formation, antioxidative and free radical-scavenging properties, and regulation of cell proliferation, apoptosis, and immune responses (51432). Diallyl sulfide and diallyl disulfide inhibited arylamine N-acetyltransferase activity and 2-aminofluorene-DNA adduct in human promyelocytic leukemia cells (HL-60) (51263).
Diallyl disulfide (DADS) was analyzed for its apoptotic effects in human cancer cells (51425). Apaf1, cystatin B, caspase-3, and FADD (fas-associated protein with death domain) expression in breast, prostate, and lung cancer cells were investigated using DADS. DADS caused caspase-3-dependent apoptosis via a Bax-triggered mitochondria pathway, activating caspase-3 and caspase-9, and causing Bax translocation and cytochrome c release.
Circulatory effects: In observational research, garlic supplementation increased calf blood flow in healthy individuals. The improvement was associated with and possibly mediated by increased plasma levels of interleukin-6 (IL-6). In this study, increased IL-6 was independent of the activation of the NO pathway (51299). In human research, garlic reduced blood viscosity, which may help reduce the risk of cardiovascular disease and cerebral vascular accidents (51394).
Coagulation effects: Garlic powder and aged garlic preparations have been shown to have antiplatelet properties in both patients with cardiovascular disease and in healthy volunteers (1874,3234,4366,4801,4802,4803). 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 (3234,4366,4799,8017,12423,51255,51494,51574,51641,51658,96013). Raw garlic appears to dose-dependently inhibit platelet cyclooxygenase and reduce serum thromboxane B2 (9874,51531,51562,51569,51572). Antiplatelet activity may be attributable to garlic constituents, including adenosine, allicin, and paraffinic polysulfides (51452). Raw garlic seems to have more potent antiplatelet properties than cooked garlic (4799,4804,15297,51562,51563). Crushing garlic before cooking might prevent some of the loss of antiplatelet activity (15297). Garlic oil does not appear to affect platelet aggregation (4805).
Cytochrome P450 effects: There is some evidence that garlic might affect the cytochrome P450 (CYP450) enzyme system. In vitro evidence suggests that garlic might inhibit several CYP450 enzymes including CYP2C9, CYP2C19, and CYP3A4 (12198). But clinical research suggests garlic oil does not affect CYP1A2, CYP2D6, or CYP3A4 (10847).
Other findings indicate that garlic might mildly inhibit CYP2D6 activity by about 9% in humans (1303). This limited inhibition is not likely to produce clinically significant increases in drugs that are metabolized by the CYP2D6 isoenzyme. However, some researchers suspect that garlic supplements that contain a significant amount of allicin can induce the CYP3A4 isoenzyme and can produce clinical significant decreases in levels of drugs metabolized by this enzyme (7027). However, in a small study, taking a specific garlic product (GarliPure Maximum Allicin Formula, Natrolm Chatsworth) 600 mg twice daily providing 3,600 mcg allicin per dose, for 12 consecutive days did not significantly affect the pharmacokinetics of docetaxel, a CYP3A4 substrate (17221).
A garlic extract, containing alliin and alliinase, does not affect the activity of CYP2D6 or CYP3A4 (10335). Clinical research suggests that garlic oil might inhibit CYP2E1 activity by 39% (10847). The ability of garlic to induce or inhibit cytochrome P450 enzymes may depend upon the presence of other constituents in the preparation that is being used.
Dermatologic effects: Garlic has been shown to treat warts and corns in human research; however, the mechanism is unclear but may be related to antiviral and enhanced immunologic effects (15030). Garlic reportedly reduced cellular proliferation in viral effected cells and exerted anti-DNA activity (15030). Garlic’s fibrinolytic effect may cause the surrounding fibrin tissue around the corn capsule to lyse and separate from the tissue (15030).
Gastroprotective effects: In vitro evidence suggests that garlic extract and commercial garlic tablets have antimicrobial activity against Helicobacter pylori, a common bacterial associated with stomach infections or peptic ulcer (51208,51242). The anti-Helicobacter pylori effects of garlic seem to be highest for the garlic constituent allicin, followed by undiluted garlic oil then garlic powder (3322). The antibacterial effect of garlic products against H. pylori appears to be dependent on the content of allicin (51208). For garlic constituents, antimicrobial activity appears to increase with the number of sulfur atoms contained in the constituent (3322).
Early evidence suggests a possible protective effect of aged garlic on intestinal toxicity induced by methotrexate (MTX) and fluorouracil (5FU) (1885,9208). Preliminary evidence suggests that garlic might interfere with the oral absorption of lead; the sulfur containing amino acids might chelate lead in the gastrointestinal tract (9202). Samgyetang, a soup made from chicken, jujube, Panax ginseng, garlic, and chestnuts, appears to offer protection from experimentally induced peptic ulcers (10249).
Genitourinary effects: Chronic garlic ingestion for 70 days has been associated with suppression of spermatogenesis in rats (51526).
Hepatoprotective effects: According to laboratory studies, S-allyl cysteine and S-allyl mercaptocysteine might protect the liver against acetaminophen and carbon tetrachloride, possibly by reducing oxidative stress (9873). Other preliminary evidence suggests S-allyl cysteine might ameliorate doxorubicin-induced cardiac and hepatic toxicity (4780). Preliminary reports regarding possible hepatoprotective effects of aged garlic extract have been conflicting (1883,1884).
Immunologic effects: Evidence from animal research suggests that garlic oil 100-200 mg/kg every other day for 2 weeks enhances lymphocyte proliferation rate and increase the production of the cytokines interleukin 2 (IL-2), interferon gamma (IFN-gamma), IL-4, and IL-10 upon stimulation with concanavalin A (51421). At low doses, garlic oil appears to enhance T cell response toward the Th1 type cytokines (e.g., IL-2 and INF-gamma) (51421). These cytokines have been associated with beneficial antitumor response (8018). At high doses, garlic oil appears to enhance Th2-type cytokines (eg, IL-4 and IL-10) at high doses (51421). Other animal research suggests that aqueous garlic solution 600 mg/kg/4 mL daily for one month decreases INF-gamma production and increases IL-4 production in phytohemagglutinin-activated rat spleen lymphocytes, suggesting that garlic may favor a humor immune response when administered at higher doses (51420).
Some in vitro evidence suggests that garlic powder extract reduces lipopolysaccharide-induced production of IL-1beta and tumor necrosis factor (TNF)-alpha in human whole blood. Garlic powder extract also appears to reduce the activity of nuclear factor (NF)-kB, a transcription factor involved in inflammation associated with autoimmune diseases such as arthritis and inflammatory bowel disease, as well as atherosclerosis (51282).
Garlic may also enhanced natural killer (NK) cell number and activity against tumor cell lines (51285,51358). However, while raw garlic juice, heated garlic juice, dehydrated garlic powder, and aged garlic extract all seem to increase NK cell activities in tumor-bearing mice, only aged garlic extract and heated garlic juice appear to inhibit the growth of tumor cells (51240).
Garlic also appears to stimulate macrophage and lymphocyte proliferation, which may protect the body against immunity suppression induced by chemotherapy or radiation treatments (8018). Animal research also suggests that long-term administration of garlic may improve age-associated decline in immune function (1882). The garlic constituent alliin appears to increase the phagocytic function of peripheral blood leukocytes and monocytes (51212).
Neurologic effects: In animal research, aged garlic extract prevented deterioration of hippocampal-based memory tasks (51389) and had antiamyloidogenic effects (51372). In vitro, S-allyl-L-cysteine protected against amyloid beta- and tunicamycin-induced neuronal death (51294). The protein TRPA1 mediates the response to pungent irritants found in garlic, and is found mainly in nociceptive neurons of peripheral ganglia and in all the mechanosensory epithelia of the inner ear (51382). In an amyotrophic lateral sclerosis transgenic mouse model, diallyl trisulfide (DATS) demonstrated neuroprotective effects (51453). DATS has activated phase II enzymes. SOD1-G93A transgenic mice were administered DATS orally (80 mg/kg daily). DATS extended disease duration and life span for around one week, induced HO-1, and decreased GFAP expression.
Ocular effects: In animal research, S-allylmercaptocysteine, a garlic-derived compound, reduced intraocular pressure; it may involve the elevation of ANP levels (51206).
Radioprotective effects: In vivo, the garlic-derived organosulfur constituent allylmethylsulfide has demonstrated radioprotective effects, possibly by downregulating the mitogen-activated protein kinases (MAPKs) and nuclear factor-kappaB (NF-kappaB)-signaling pathway (51431).
Skeletal effects: In animal research, garlic suppressed bone loss due to estrogen deficiency (51347). In ovariectomized rats, garlic may inhibit bone resorption, as evidenced by alterations of serum alkaline phosphatase activity; serum tartrate-resistant acid phosphatase activity; urinary excretion of calcium, phosphate, and hydroxyproline; and the urinary calcium-to-creatinine ratio (51310). In animal research, garlic prevented bone mineral loss by promoting intestinal transference of calcium through the partial revival of the serum estrogen titer (51367).
Vascular effects: Vasorelaxant properties of garlic have been noted in multiple preclinical studies (51271,51293,51297). Cutaneous microcirculation has been shown to increase in humans following ingestion of 600 mg of garlic due to vasodilation of precapillary arterioles (51222,51424). In patients with hypertension, 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) (4812,51533,51661). It has been suggested that allicin is the component of garlic responsible for nitric oxide-mediated effects (51662). Garlic may also attenuate age-related increases in aortic stiffness, which may improve vasoelasticity and protect against cardiovascular diseases (4797).
Weight loss effects: In animal research, the allyl-containing polysulfides in garlic have been found to be responsible for increasing thermogenesis (51205). These compounds enhance thermogenesis by increasing noradrenaline secretion via beta-adrenergic stimulation, enhance noradrenaline and adrenaline excretion, and reduce body fat accumulation by increasing triglyceride catabolism by the elevation of thermogenesis in brown adipose tissue (BAT) and increasing uncoupling protein (UCP) (51205).
Wound healing: In animal research, wound-healing effects were attributed to angiogenic properties of aged garlic solution (51427). The exact mechanism is not well understood.
Absorption: Allicin and other garlic constituents, including S-allyl cysteine and gamma-glutamyl-cysteine, are well absorbed (51541,51587). Garlic compounds are rapidly absorbed through mucous membranes and skin.
Metabolism: Metabolism of the garlic constituent S-allyl cysteine occurs on the liver and kidney (51541). Metabolites of garlic include allicin (active), ALMA (N-acetyl-S-allyl-L-cysteine or allyl mercapturic acid), diallyl disulfide (metabolite of allicin), allyl-mercaptan (a metabolite of allicin and diallyl disulfide), allyl methyl sulfide (a metabolite of allicin and diallyl disulfide), allyl methyl sulfoxide (AMSO) (a metabolite of allicin and diallyl disulfide), and allyl methyl sulfone (AMSO[sub 2]) (a metabolite of allicin and diallyl disulfide) (51272,51565,51663). The highest amounts of diallyl disulfide metabolites have been noted after 48-72 hours (51272). Maximal concentrations of the vinyldithiins, transformation products of allicin, occur 15-30 minutes after oral absorption (51663).
Excretion: Garlic is excreted primarily in urine and feces, and possibly via bile or intestinal mucosa (51540). In human research, the elimination half-life of N-acetyl-S-allyl-L-cysteine is approximately six hours following ingestion of dried and fresh garlic (51565). In laboratory research, garlic has been found to follow zero-order kinetics (51306).