Garlic is an herb widely used for the treatment and prevention of heart disease and cancer. Research suggests that tablets with dehydrated garlic powder may modestly reduce total cholesterol for up to 12 weeks. Garlic's long-term effects on cholesterol and heart health remain unclear.
Early evidence suggests that garlic may slightly reduce blood pressure and prevent blood clotting. Several studies report that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of several cancer types, including stomach and colon.
Multiple cases of bleeding have been associated with garlic use. Caution is warranted in people who are at risk of bleeding and before some surgical and dental procedures.
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.
Numerous human studies report that garlic may lower blood pressure, particularly systolic blood pressure. It is unclear if effects are more pronounced in people with high blood pressure vs. normal blood pressure.
Multiple studies in humans have reported small reductions in total blood cholesterol and low-density lipoproteins (LDL or "bad" cholesterol) over short periods of time. Garlic lacks effects on high-density lipoproteins (HDL or "good" cholesterol).
Several studies have concluded that garlic may have a positive impact on heart disease risk. Evidence suggests that garlic may reduce the incidence of heart attack or cardiac death.
Preliminary evidence suggests that garlic may be beneficial against oral microorganisms like Streptococci and may be an alternative to the antiseptic chlorhexidine. Further research is needed before a conclusion can be made.
Several studies describe garlic applied to the skin to treat fungal infections, including yeast infections. Additional research is needed before a conclusion can be drawn.
Research suggests modest short-term reductions in total cholesterol and low-density lipoprotein (LDL or "bad" cholesterol) levels with garlic supplements. Insufficient evidence exists on the effects of garlic on arthrosclerosis prevention or treatment. Further research is warranted in this area.
Based on preliminary study, allicin (the major biologically active component of garlic) supplementation may reduce exercise induced muscle damage. The mechanism may be associated with allicin's antioxidant effects. Further studies are needed to confirm these findings.
A single dose of garlic has increased endurance performance. Long-term use of garlic for this purpose should be investigated.
Preliminary research suggests a garlic combination supplement may improve symptoms of benign breast disease. Additional study is needed using garlic alone.
Preliminary human studies suggest that regular consumption of garlic (particularly unprocessed garlic) may reduce the risk of several cancer types, including gastric and colorectal cancer. Further well-designed studies are needed in this area.
Preliminary evidence suggests that garlic reduces chest pain by relieving spasm of the heart vessels and preventing blood clots. Additional studies are needed before a conclusion can be made.
A study has reported benefits from a combination garlic therapy on venous ulcers. Further research is warranted on this topic.
Garlic supplementation has increased calf blood flow in healthy people. Further research is needed before conclusions can be made.
Preliminary reports suggest that garlic may reduce the severity of upper respiratory tract infections. In non-human studies, garlic has displayed anti-bacterial and anti-viral properties. Additional research is needed in this area.
Garlic has been studied in combination with other therapies for cystic fibrosis. Further research is warranted.
The dental effects of garlic have been studied. Further research is needed before firm conclusions may be made.
Familial hypercholesterolemia is a genetic disorder in which very high cholesterol levels are inherited. The effect of garlic on familial hyperlipidemia is unclear. Further research in this area is needed to draw a conclusion.
Garlic has been studied for its use in gastric lesions. Further research is needed before firm conclusions may be made.
Preliminary evidence suggests that a combination product with garlic (Karinat®) may be beneficial for manging chronic atrophic gastritis, a precursor of stomach cancer. Additional evidence is needed before a conclusion can be made.
Application of garlic gel on the skin may be beneficial for treating hair loss. Additional study is needed on this topic.
Research suggests modest short-term reductions in total cholesterol and low-density lipoprotein levels (LDL or "bad" cholesterol) with oral garlic supplements. Long-term effects on lipids and atherosclerosis are unclear. There is limited evidence regarding the effects of garlic on heart attack, cardiac morbidity and mortality.
Garlic's role in improving clinical manifestations of lead poisoning has been studied. Further research is warranted.
In non-human studies, garlic has shown activity against bacteria and viruses. Several human case studies have examined the effects of garlic on H. pylori infection and found mixed results. Further research is needed to clarify these findings.
The effect of a hepatitis medication plus garlic oil has been studied. Further research of garlic alone is warranted.
Hepatopulmonary syndrome is shortness of breath in people with liver disease. Garlic has been studied in people with hepatopulmonary syndrome. Further research is needed before firm conclusions may be drawn.
A preliminary study lacked support regarding garlic consumption for repelling mosquitoes. Well-designed clinical trials are required before conclusions may be made.
Preliminary evidence suggests that a combination product containing garlic may be beneficial for ear pain caused by middle ear infections. Additional evidence is needed before a conclusion may be made.
Experts suggest that international travelers eat fresh garlic to prevent intestinal parasites. There are mixed results regarding the use of garlic in the treatment of parasitic infections. Further evidence is needed before a conclusion may be made.
Research suggests modest short-term reductions in total cholesterol and low-density lipoprotein levels (LDL or "bad" cholesterol) with oral garlic supplements. There is currently insufficient evidence demonstrating effects of garlic on peripheral vascular disease. Further research is warranted in this area.
In the available research, garlic administration lacked significant effects on the incidence of preeclampsia, systolic or diastolic blood pressure. Well-designed studies are still required.
Initial evidence suggests that aged garlic extract may reduce the number of damaged red blood cells in patients with sickle-cell anemia. Well-designed clinical trials are required before conclusions may be made.
Preliminary evidence suggests that dried garlic powder may benefit people with systemic sclerosis. Well-designed clinical trials are required before conclusions may be made.
Early research has reported fewer tick bites in people receiving garlic. However, there is a lack of sufficient data for or against the use of garlic as an insect repellent.
It is unclear if garlic may decrease glucose concentrations and increase insulin secretion. Additional research is needed in this area.
According to preliminary research, garlic extract applied to the skin may be beneficial in treating warts and corns. This effect may be due to garlic's antiviral, immune-stimulating, or blood clot prevention properties. Further research is needed.
* 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 for this use (it may not work) F: Strong scientific evidence against this use (it likley does not work)
Tradition / Theory
The below uses are based on tradition, scientific theories, or limited research. 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. There may be other proposed uses that are not listed below.
For an antifungal, 1 milligram per kilogram of body weight of a garlic extract (Allidridium) diluted into 500 milliliters of saline has been injected in the blood over four hours daily for less than one month.
For athletic injuries, 80 milligrams of allicin (garlic component) has been taken by mouth for 14 days.
For athletic performance, a single dose of 900 milligrams of dried garlic has been taken by mouth.
For cancer, aged garlic extract capsules (containing 2.4 milliliters of garlic extract) or 500 milligrams of aged garlic extract has been taken by mouth daily for 6-12 months. Additionally, 1 milliliter of aqueous garlic extract per kilogram of weight has been taken by mouth daily for one month.
For cirrhosis (liver disease), 250 milligram capsules containing garlic oil (Garlic Pearls, Ranbaxy, India) have been taken by mouth in two divided doses with meals for 9-18 months. The daily dose of garlic capsules provided 1-2 grams per square meter of garlic oil.
For clogged arteries, 900 milligrams of a dehydrated garlic powder tablet (Kwai®) has been taken by mouth in single or divided doses for up to four years. A suggested dose for clogged arteries is 3-5 milligrams of allicin (one clove or 0.5-1 gram of dried powder) daily by mouth.
For common cold / upper respiratory tract infection, 180 milligrams of allicin (Allimax®) has been taken by mouth daily for 12 weeks. Two capsules containing aged garlic extract (AGE) powder have been taken by mouth twice daily for 90 days. The suggested dose for respiratory infections is 2-4 grams of garlic dried bulb or 2-4 milliliters of garlic alcoholic extract (1:5, 45% ethanol) taken by mouth three times daily.
For cystic fibrosis, capsules containing 656 milligrams of garlic oil have been used once daily with evening meals for eight weeks. One garlic capsule has been taken daily for eight weeks.
For dental conditions, 20 drops of garlic solution (40 milligrams per milliliter) has been used in the mouth three times daily for four weeks.
For hair loss, 5% garlic gel has been applied to the scalp four times daily for three months.
For heart disease risk and prevention, one tablet of Allicor® (150 milligrams of garlic powder) has been taken by mouth two times daily for 12 months. 6-10 grams of a garlic ether extract has been taken by mouth for three years.
For heavy metal/lead toxicity, capsules containing 400 milligrams of dried powder garlic have been taken by mouth three times daily for four weeks
For high cholesterol, 10-7,200 milligrams of garlic has been taken in powder, tablet, oil, extract, or allicin form by mouth daily in single or divided doses for up to 7.3 years.
For high blood pressure, 600-2,400 milligrams of garlic powder (Kwai® or Allicor®) or aged garlic extract (Kyolic®) in single or divided doses has been taken by mouth daily for up to 12 weeks.
For Helicobacter pylori infection, 4,200 micrograms of allicin (the main ingredient in garlic) daily in conjunction with standard treatment has been taken by mouth for 14 days. Additionally, 400 milligrams of Kyolic aged garlic extract plus 2 milligrams of steam-distilled garlic oil has been taken by mouth twice daily for seven years.
For oral candidiasis (yeast infection), garlic paste has been applied in the mouth four times daily for 14 days.
For a mosquito repellent, four garlic capsules as a single dose have been taken by mouth
For peripheral vascular disease, 800-900 milligrams of dehydrated garlic (Kwai®) has been taken by mouth daily for 12 weeks.
For pre-eclampsia (high blood pressure during pregnancy), 800 milligrams of garlic (Garlet®, 1,000 micrograms of allicin and ajoene) has been taken by mouth daily for up to eight weeks.
For sickle-cell anemia (blood cell disorder), 5 milliliters of aged garlic extract has been taken by mouth daily for four weeks.
For stomach cancer prevention, garlic supplementation for up to 7.3 years (dosage unknown) has been taken by mouth.
For systemic sclerosis (thickening of skin), 900 milligrams of dried garlic powder has been taken by mouth for seven days
For a tick repellant, 1,200 milligrams of Allium capsules have been taken by mouth daily for eight weeks
For type 2 diabetes, 300-900 milligrams of Allicor® or a dehydrated garlic preparation (Kwai®) hase been used in single or divided doses for up to 24 weeks.
For warts, water-based garlic extract has been applied twice daily on warts. A lipid extract was also applied twice daily on people with warts and corns.
Children (younger than 18 years)
Safety or effectiveness of garlic supplements is unclear in children.
For common cold/ upper respiratory tract infection, extended-release garlic tablets (Allicor® 600 milligrams) has been taken by mouth over a five-month period.
For familial hyperlipidemia (inherited high cholesterol), 900 milligrams of dehydrated garlic powder tablets (Kwai®) has been taken by mouth in three divided daily doses.
For parasitic infections, 5 milliliters of garlic extract in 100 milliliters of water has been taken by mouth in two doses daily, or a commercial preparation of 1.2 milligrams has been taken by mouth twice daily for three days. Additionally, 8 grams of a garlic infusion has been taken by mouth daily for five days.
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.
Avoid in people with a known allergy or sensitivity to garlic, any of its constituents, or to other members of the Liliaceae (lily) family, including hyacinth, tulip, onion, leek, and chives.
Allergic reactions have been reported with garlic taken by mouth, inhaled, or applied to the skin. These reactions have included asthma, closing up of the lung airways, dryness and splitting of the lips, hives, inflammation of the intestines and stomach, narrowing of the coronary artery, and skin inflammation and swelling.
Severe reactions may occur, including throat swelling and difficulty breathing (anaphylaxis). Fresh garlic applied to the skin may be more likely to cause rashes than garlic extract. Commercially available gloves may not offer adequate protection for the allergic reaction associated with garlic allergy.
Side Effects and Warnings
Garlic is likely safe when consumed in amounts usually found in foods in non-allergic or non-sensitive people.
Garlic is possibly safe when used as a dietary supplement in suggested doses in healthy adults. Garlic is possibly safe when garlic extracts are used on the skin for 1-2 months in the treatment of warts and corns.
Garlic may increase the risk of bleeding. Caution is advised in people with bleeding disorders or taking drugs that may increase the risk of bleeding. Dosing adjustments may be necessary.
Garlic may lower blood sugar levels. Caution is advised in people with diabetes or hypoglycemia, and in those taking drugs, herbs, or supplements that affect blood sugar. Blood glucose levels may need to be monitored by a qualified healthcare professional, including a pharmacist, and medication adjustments may be necessary.
Use cautiously during breastfeeding, in people with gastrointestinal disorders or prone to gastric irritation, peptic ulcer disease, skin disorders, or thyroid disorders. Use cautiously when garlic is injected in the blood in people with liver or kidney disease.
Use cautiously in people taking agents for the brain, agents for the skin, agents that widen blood vessels, antiretroviral agents (particularly protease inhibitors), blood pressure lowering agents, cholesterol-lowering agents, agents metabolized by the liver, estrogens, or thyroid agents.
Avoid in people with a known allergy to garlic, its parts, or other members of the Liliaceae or Alliaceae families, including hyacinth, tulip, onion, leek, and chives. Avoid garlic applied to the skin in young children or infants, and before surgical or dental procedures. Avoid large amounts of garlic during pregnancy.
Garlic may also cause acid reflux, anorexia, asthma, bad breath, bleeding after surgery, blisters, blood pressure reduction, body odor, botulism (paralyzing illness), bowel obstruction, burns to the skin, burping, change in bacteria in the stomach, chest pain, chills, constipation, coughing up of blood, darkening of the skin, dead tissue, decrease in blood clotting time, diarrhea, difficulty breathing, dizziness, drowsiness, dryness and splitting of the lips, eczema, euphoria, eye hemorrhage during surgery, facial flushing, fever, gas, gastrointestinal irritation or burning (including mouth, esophagus and stomach), gout, heart attack, heartburn, high white blood cell concentration, high heart rate, hives, hypothyroidism (underactive thyroid) and reduced iodine uptake, increased appetite, increased colic risk in infants, increased eye pressure, increased insulin secretion, increased sweating, inflammation of stomach and intestines, inhibition of amyloid production, internal bleeding near the kidney, itching, kidney damage, lip inflammation, liver damage, local irritation, low back pain, lower cholesterol, nausea, neurological effects, painful urination or excessive large volume of urine, pemphigus (blistering of the skin or mucus membranes), redness, self-inflicted lesions of the skin, skin inflammation, sleeping problems, suppression of sperm production, ulcers, uterine contractions, vomiting, and weight loss,
Note: Dishes containing generally acceptable doses of raw garlic are unlikely to increase the risk of bleeding before surgery.
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 or stimulation of uterine contractions. 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 reported increased nursing time, milk odor, and milk consumption. The safety of garlic supplements during breastfeeding is unclear.
Colic has been associated with maternal garlic consumption. Garlic in a combination treatment purportedly increased breast milk. Garlic in breast milk has been reported to increase nursing time.
Garlic may lower blood sugar levels. Caution is advised when using medications that may also lower blood sugar. People taking drugs for diabetes by mouth or insulin should be monitored closely by a qualified healthcare professional, including a pharmacist. Medication adjustments may be necessary.
Garlic may increase the risk of bleeding when taken with drugs that increase the risk of bleeding. Some examples include aspirin, anticoagulants ("blood thinners") such as warfarin (Coumadin®) or heparin, anti-platelet drugs such as clopidogrel (Plavix®), and non-steroidal anti-inflammatory drugs such as ibuprofen (Motrin®, Advil®) or naproxen (Naprosyn®, Aleve®).
Garlic may interfere with the way the body processes certain drugs using the liver's "cytochrome P450" enzyme system. As a result, the levels of these drugs may be increased in the blood, and may cause increased effects or potentially serious adverse reactions. People using any medications should check the package insert, and speak with a qualified healthcare professional, including a pharmacist, about possible interactions.
Many tinctures contain high levels of alcohol, and may cause nausea or vomiting when taken with metronidazole (Flagyl®) or disulfiram (Antabuse®).
Because garlic contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
Garlic may cause low blood pressure. Caution is advised in people taking drugs that lower blood pressure.
Garlic may also interact with acetaminophen; agents for cancer, glaucoma, obesity, osteoporosis; agents for the blood, brain, heart, kidneys, intestines, skin, stomach; agents that alter eye pressure; agents that alter immune function; agents that induce abortion; agents that widen or relax blood vessels; agents toxic to the liver; anthelmintics; antibiotics; antifungals; antiparasitics; antiretrovirals; antivirals; cholesterol lowering agents; clofibrate; disulfiram; docetaxel; estrogens; fertility agents; iodine; isoniazid; metronidazole; nonsteroidal anti-inflammatory agents (NSAIDS); performance-enhancing agents; potassium salts; thyroid hormones; weight loss agents.
Interactions with Herbs and Dietary Supplements
Garlic may lower blood sugar levels. Caution is advised when using herbs or supplements that may also lower blood sugar. Blood glucose levels may require monitoring, and doses may need adjustment.
Garlic may increase the risk of bleeding when taken with herbs and supplements that are believed to increase the risk of bleeding. Multiple cases of bleeding have been reported with the use of Ginkgo biloba, and fewer cases with garlic and saw palmetto. Numerous other agents may theoretically increase the risk of bleeding, although this has not been proven in most cases.
Garlic may interfere with the way the body processes certain herbs or supplements using the liver's "cytochrome P450" enzyme system. As a result, the levels of other herbs or supplements may become too high in the blood. It may also alter the effects that other herbs or supplements possibly have on the P450 system.
Because garlic contains estrogen like chemicals, the effects of other agents believed to have estrogen-like properties may be altered.
Garlic may cause low blood pressure. Caution is advised in people taking herbs or supplements that lower blood pressure.
Garlic may also interact with anthelmintics; antibacterials; antifungals; antioxidants; antiparasitics; antivirals; cholesterol lowering herbs and supplements; EPA (eicosapentaenoic acid) and fish oil; fertility herbs and supplements; ginkgo; herbs and supplements for cancer, glaucoma, obesity, osteoporosis; herbs and supplements for the blood, brain, heart, kidneys, intestines, skin, stomach; herbs and supplements that alter eye pressure; herbs and supplements that alter immune function; herbs and supplements that induce abortion; herbs and supplements that widen blood vessels; herbs and supplements toxic to the liver; performance-enhancing herbs and supplements; potassium; Pycnogenol®; selenium; thyroid herbs and supplements; weight loss herbs and supplements; zinc.
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Bakhshi, M., Taheri, J. B., Shabestari, S. B., Tanik, A., and Pahlevan, R. Comparison of therapeutic effect of aqueous extract of garlic and nystatin mouthwash in denture stomatitis. Gerodontology. 2012;29(2):e680-e684.
Higashikawa, F., Noda, M., Awaya, T., Ushijima, M., and Sugiyama, M. Reduction of serum lipids by the intake of the extract of garlic fermented with Monascus pilosus: a randomized, double-blind, placebo-controlled clinical trial. Clin.Nutr. 2012;31(2):261-266.
Kianoush, S., Balali-Mood, M., Mousavi, S. R., Moradi, V., Sadeghi, M., Dadpour, B., Rajabi, O., and Shakeri, M. T. Comparison of therapeutic effects of garlic and d-Penicillamine in patients with chronic occupational lead poisoning. Basic Clin.Pharmacol.Toxicol. 2012;110(5):476-481.
Kundakovic, T., Milenkovic, M., Zlatkovic, S., Nikolic, V., Nikolic, G., and Binic, I. Treatment of venous ulcers with the herbal-based ointment Herbadermal(R): a prospective non-randomized pilot study. Forsch.Komplementmed. 2012;19(1):26-30.
Lee, M. H., Kim, Y. M., and Kim, S. G. Efficacy and tolerability of diphenyl-dimethyl-dicarboxylate plus garlic oil in patients with chronic hepatitis. Int.J.Clin.Pharmacol.Ther. 2012;50(11):778-786.
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Nantz, M. P., Rowe, C. A., Muller, C. E., Creasy, R. A., Stanilka, J. M., and Percival, S. S. Supplementation with aged garlic extract improves both NK and gammadelta-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. Clin.Nutr. 2012;31(3):337-344.
Ried, K., Frank, O. R., and Stocks, N. P. Aged garlic extract lowers blood pressure in patients with treated but uncontrolled hypertension: a randomised controlled trial. Maturitas 2010;67(2):144-150.
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Sobenin, I. A., Pryanishnikov, V. V., Kunnova, L. M., Rabinovich, Y. A., Martirosyan, D. M., and Orekhov, A. N. The effects of time-released garlic powder tablets on multifunctional cardiovascular risk in patients with coronary artery disease. Lipids Health Dis. 2010;9:119.
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Zhou, Y., Zhuang, W., Hu, W., Liu, G. J., Wu, T. X., and Wu, X. T. Consumption of large amounts of Allium vegetables reduces risk for gastric cancer in a meta-analysis. Gastroenterology 2011;141(1):80-89.
The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.