Garlic
Allium sativum · Amaryllidaceae (formerly Liliaceae) · fresh or dried bulb
Also known as Lasuna and Rasona (Ayurveda), Da Suan (Traditional Chinese Medicine), Lahsun (Hindi), stinking rose, poor man's treacle
- Hot
- Pungent
- Drying
- Antimicrobial
- Expectorant
- Carminative
- Diaphoretic
- Circulatory support
Educational content, not medical advice. Nothing on this page is a substitute for care from a qualified healthcare provider. Do not stop or change a prescribed medication based on anything you read here. Garlic in medicinal amounts can affect bleeding and change how the body handles certain drugs, so talk with your doctor or pharmacist before using it beyond food amounts if you take medication or have surgery scheduled.
About Garlic
Garlic is the bulb of Allium sativum, a perennial in the onion genus. Each bulb is a cluster of 8 to 20 wedge-shaped cloves wrapped in a shared papery skin.1 King's American Dispensatory filed it under Liliaceae, the lily family, and older texts still do. Modern botany places the onion genus in Amaryllidaceae, the amaryllis family. Either name points to the same plant.
- Native range: Central Asia and northeastern Iran. King's called it a native of Sicily, which reflects where Europeans first met it in cultivation rather than where it originated.1
- Where it grows now: nearly everywhere with a cold winter and a dry summer. Cloves planted in late autumn root over winter and bulb up by midsummer. It grows well in Montana.
- Identifying the bulb: a compound bulb of compressed cloves around a central stem base, with a warm, acrid taste and a strong sulfurous smell once cut. Whole intact cloves have almost no odor; the smell appears when the cell walls break.1
- Fresh versus dried: the bulb loses about half its weight in drying but very little of its smell or taste. King's advised using it fresh.1
Who has used it
- Ayurveda calls it Lasuna or Rasona, the latter often explained as "lacking one taste," since garlic is said to carry five of the six tastes and miss only sour.8
- Traditional Chinese Medicine calls it Da Suan and files it among the herbs that expel parasites.10
- Western herbalism carried it from Egyptian, Greek, and Roman use into the European pharmacopoeias and the American Eclectic and Physiomedical physicians of the 1800s.1,4 Germany's Commission E and the European Medicines Agency both hold current monographs on it.5,6
Traditional Use
The traditions below describe how practitioners have used garlic. These are historical and cultural records, not instructions. None of this is medical advice.
Energetics
Hot, pungent, and drying in every system that classifies it. Garlic pushes warmth and circulation outward, opens the lungs, dries damp congestion, and stimulates a sluggish, cold digestion. It suits people who run cold and damp with mucus, poor circulation, and heavy digestion. It aggravates heat, dryness, and irritation.
Western herbalism: the Eclectics and Physiomedicalists
King's American Dispensatory classifies garlic as a stimulant, diuretic, expectorant, and rubefacient (an agent that reddens and warms the skin), and credits every effect to the absorption of its volatile oil, which the body then excretes through the skin, kidneys, and lungs.1 The Eclectic physicians, a school of American doctors active from the mid 1800s into the 1930s, used it:
- for coughs, catarrh (excess mucus), whooping cough, and hoarseness, often as a syrup of the juice for children1,2
- for worms1
- externally as a poultice along the spine and over the chest of infants with pneumonia, and over the bladder when urine was retained from a sluggish bladder1,3
- as ear drops of garlic juice, sweet almond oil, and glycerin in equal parts, for hearing loss the authors attributed to wax buildup or weak ear tissues1
William Cook's Physiomedical Dispensatory describes the bulbs as very stimulating, moderately relaxing, and very diffusible, exciting the mucous secretions, easing digestion in sluggish stomachs, and promoting expectoration. Cook also recorded the limits: large quantities or long external application excite the circulation enough to cause hot skin, a flushed face, and headache.4 King's noted that large doses cause nausea, vomiting, and purging, and that the oil blisters skin on contact.1
Germany's Commission E later approved garlic as a supportive measure alongside diet for elevated blood lipids and for preventing age-related vascular changes.5 The European Medicines Agency lists it as a traditional remedy used as an adjuvant in the prevention of atherosclerosis and for relief of common cold symptoms.6
Ayurveda: Lasuna
Sebastian Pole classifies garlic as pungent, light, and heating. It reduces kapha (the heavy, damp, cold quality) and vata, and increases pitta (heat).8 Its traditional roles include:
- kindling agni, the digestive fire, and clearing cold, stagnant digestion
- supporting the lungs in wet, congested patterns and encouraging free breathing
- warming circulation where there is coldness or weakness, and rejuvenating vata
- as a paste or infused oil on the skin for fungal patches and ringworm, and warmed oil in the ear8,9
Pole cautions against medicinal doses in high pitta, in hyperacidity and ulcers, and in pregnancy, and notes garlic can irritate the gut lining in high doses.8
Traditional Chinese Medicine: Da Suan
Bensky's Chinese Herbal Medicine: Materia Medica describes Da Suan as acrid and warm, entering the Large Intestine, Lung, Spleen, and Stomach channels. Its listed actions are to kill parasites (hookworm, pinworm, and scalp tinea), transform food stagnation, warm the middle and expel cold-damp, resolve toxicity, and reduce swelling in early-stage sores when applied topically. It is given for diarrhea and dysentery from epidemic toxins or food stagnation, both by mouth and as an enema. Bensky contraindicates it in yin deficiency with heat signs and in heat affecting the eyes, mouth, throat, or gums.10 Christopher Hobbs summarizes Chinese clinical reports of garlic decoctions and enemas in bacterial and amebic dysentery, with purple-skinned fresh cloves judged more active than white.11
Constituents and What They Do
Garlic's chemistry changes the moment you cut it. An intact clove holds a stable, odorless sulfur compound called alliin and an enzyme called alliinase in separate compartments. Crushing brings them together and alliinase converts alliin to allicin within seconds. Allicin is unstable and breaks down into a family of sulfur compounds that differ by preparation, which is why raw garlic, cooked garlic, garlic oil, and aged extract are not the same medicine.7,9 One milligram of alliin yields about 0.45 mg of allicin.7
| Constituent | Where it sits | What studies show |
|---|---|---|
| Alliin | About 1 percent of carefully dried powder; standardized products are set at 1.3 percent alliin9 | Inactive on its own. It is the storage form that becomes allicin when the clove is cut. Water-soluble and heat-stable, but the enzyme that activates it is not.7 |
| Allicin | Formed on crushing; European Pharmacopoeia garlic powder must release at least 0.45 percent7 | Kills bacteria and fungi in laboratory work and is the source of the smell. The compound tested in the one cold-prevention trial.16 Reactive enough to blister skin when raw garlic is held against it.20 Decays within hours to days; heat destroys the enzyme that makes it. |
| Diallyl sulfides and ajoene | Breakdown products of allicin; the volatile oil is 0.1 to 0.36 percent of the bulb7 | The compounds in garlic oil and oil macerates. Ajoene and the sulfides inhibited platelet clumping in laboratory work, the basis of the bleeding caution. King's credited every medicinal effect to this oil.1,7 |
| S-allylcysteine | Forms during long aging in water or dilute alcohol; the marker for aged garlic extract | Stable, odorless, and water-soluble. The compound measured in the aged garlic blood pressure trials, at 1.2 mg per 1.2 g of extract.14 |
| Fructans | Storage carbohydrate of the bulb | Feed gut bacteria. The prebiotic effect Herbal Reality describes rests on these.9 Also the reason large amounts of garlic cause gas in some people. |
| Gamma-glutamyl peptides, saponins, flavonoids, selenium | Minor | Contribute to antioxidant activity in laboratory work. No human outcome data tied to them alone.7 |
What the Research Shows
Garlic has more human trials behind it than almost any kitchen herb, and the results split by question. Blood pressure has the most consistent signal, a modest drop in people who start high, though much of that work used one commercial aged extract and was funded by its maker. Cholesterol is the opposite story: the largest independent trial found nothing. Cold prevention rests on a single trial run by someone with a commercial stake. The drug interaction with saquinavir is the best-documented finding on the page, and it is a harm rather than a benefit. Nobody should adjust blood pressure, cholesterol, or antiviral medication around garlic.
Raw garlic and two supplements versus placebo for cholesterol
- Design: 192 adults with moderately elevated LDL (130 to 190 mg/dL) randomized to raw garlic in a sandwich, a powdered garlic tablet, an aged garlic extract capsule, or placebo, six days a week for six months, with monthly blood draws.
- Findings: LDL did not fall in any group. Changes were within a few mg/dL of zero, and placebo did slightly better than any garlic arm. HDL, triglycerides, and the total-to-HDL ratio did not change.13
- Dose: the equivalent of one 4 g clove per day, with the supplements matched to that amount.
- Limitations: the trial covered people with moderate LDL only, so it cannot rule out an effect in people with higher levels. Funded by the National Institutes of Health with no industry money, which makes it the most independent trial on this page.
Pooled trials: garlic and blood pressure
- Design: a meta-analysis (a statistical pooling of separate trials) of 20 randomized controlled trials with 970 participants, comparing garlic preparations with placebo over 8 to 26 weeks.
- Findings: systolic pressure fell by about 5 mmHg and diastolic by about 2.5 mmHg overall. In participants who started with high blood pressure the systolic drop was larger, around 8 to 9 mmHg. The same review reported modest total cholesterol reductions in people with elevated levels over two months or more.14
- Dose: varied; the author's own trials used 240 to 2,400 mg of Kyolic aged garlic extract daily.
- Limitations: the author ran several of the included trials, and those trials were funded and supplied by Wakunaga, the maker of Kyolic. The review itself appeared in a journal supplement from a Wakunaga-sponsored symposium. Preparations and durations differ across trials, and blood pressure was often measured over only 12 weeks.
An allicin supplement for preventing colds
- Design: 146 volunteers randomized to one capsule containing 180 mg of allicin or placebo daily for 12 weeks during cold season, tracking colds in a diary.
- Findings: 24 colds in the garlic group versus 65 on placebo, and 111 sick days versus 366. Days to recover from a cold were similar in both groups.15,16
- Dose: 180 mg allicin daily.
- Limitations: the only trial that met Cochrane's inclusion criteria in a search of the whole literature, and Cochrane concluded the evidence is insufficient. Colds were self-reported. Cochrane noted the analysis and outcomes did not appear to be set in advance. The sole author is affiliated with the Garlic Centre, a UK organization that markets allicin supplements, and the capsule was a commercial product.
Aged garlic extract, immune cells, and cold symptoms
- Design: 120 healthy adults randomized to 2.56 g of aged garlic extract or placebo daily for 90 days during cold and flu season, with immune cell activity measured in blood and symptoms tracked in diaries.
- Findings: natural killer and gamma-delta T cells were more active in the garlic group. The number of colds and flu episodes did not differ between groups, but the garlic group reported fewer symptom days and fewer days of missed work or school.17
- Dose: 2.56 g aged garlic extract daily.
- Limitations: funded by Wakunaga of America, the maker of the extract tested. The primary finding (no difference in number of illnesses) is the weaker one for the product; the secondary symptom findings were self-reported. Aged extract contains almost no allicin, so this trial does not speak to raw garlic.
Garlic caplets and saquinavir blood levels
- Design: 10 healthy volunteers took saquinavir, an HIV protease inhibitor, for 4 days at baseline, then took garlic caplets twice daily for 3 weeks with saquinavir repeated in the final 4 days, then a 10-day washout and a third saquinavir run.
- Findings: with garlic on board, total saquinavir exposure fell by 51 percent, trough levels by 49 percent, and peak levels by 54 percent. After the washout, levels recovered only to 60 to 70 percent of baseline.18
- Dose: two caplets of a commercial allicin-standardized product daily.
- Limitations: 10 participants, healthy rather than HIV-positive, and one product. The mechanism (likely induction of gut enzymes that break the drug down) is inferred rather than measured. National Institutes of Health study, no industry funding. This is the finding behind the EMA's contraindication below.
Chemical burns from raw garlic on skin
- Design: a search of PubMed, Google Scholar, and ResearchGate for published burn injuries caused by raw garlic on skin, yielding 32 articles and 39 patients.
- Findings: patients ranged from 3 months to 80 years old. Burns were most often on the legs and head, and nearly all followed crushed garlic held against skin under a bandage or cloth for hours, usually as a home remedy. The authors advise against applying raw garlic to skin or mucous membranes.20
- Dose: a single crushed clove was enough in several cases.
- Limitations: case reports capture only injuries that reached a hospital and got written up, so the true rate is unknown in both directions. No industry funding.
Safety and Cautions
Not medical advice. Herbs contain active compounds that can interact with medications and health conditions. Garlic at food amounts has thousands of years of safe use. The cautions below apply to medicinal amounts, supplements, and raw garlic on skin. Talk with your healthcare provider or pharmacist before using it beyond cooking if any of these apply to you.
Where Francis Brinker's Herbal Contraindications and Drug Interactions is cited, his evidence grade follows in parentheses: "empirical" means clinical observation or case reports, "speculative" means an inference from mechanism or from a related substance, and "human study," "animal," "ex vivo," or "in vitro" name the kind of research behind the statement.24
Medication interactions
- Saquinavir and ritonavir (HIV medication). The EMA contraindicates garlic preparations with these drugs because garlic caplets cut saquinavir blood levels by half in a human trial, with a risk of treatment failure and viral resistance.6,18 Brinker notes the caplets supplied 9.3 mg allicin and 22.4 mg alliin daily, about two 4 g cloves, and that levels were still 35 percent below baseline after a 10-day washout (human study). He also records that 1.8 g of a standardized extract twice daily for 14 days did not change alprazolam metabolism in 14 volunteers (human study), and that fresh and aged extracts inhibited P-glycoprotein in a dish, which would push saquinavir levels the other way (in vitro).24 Anyone on antiretroviral therapy should keep garlic to food amounts and check with their prescriber.
- Blood thinners and antiplatelet drugs. The sources disagree. The EMA advises caution because garlic may lengthen bleeding time, and case reports describe raised INR in people on warfarin who added garlic products.6,9 Hoffmann and Pole both carry the caution.8,12 Brinker reports two patients whose INR doubled on garlic pearls or tablets (human case reports), notes those reports have been called unevaluable for lack of detail, and then cites the human trials behind the concern: garlic tablets at 400 mg twice daily for 12 weeks cut spontaneous platelet aggregation by 59 percent against placebo in 80 patients, 800 mg of powder for 4 weeks reduced circulating platelet aggregates in 30 people, and about 3 g of fresh garlic daily lowered thromboxane B2 (a clotting signal) by 20 percent at 4 weeks and 90 percent at 16 weeks. He concludes anticoagulants are likely enhanced and that fresh garlic above 5 g daily is contraindicated with warfarin (speculative).24 Against that: 10 ml of aged garlic extract daily for 12 weeks produced no bleeding in 22 warfarin patients, and an enteric-coated tablet from 2 g fresh garlic taken twice daily for 3 weeks did not change INR or warfarin blood levels in 12 volunteers given a single warfarin dose (human studies).19,24 Brinker adds that ajoene potentiated indomethacin and dipyridamole on platelets in a dish, and that prolonged high doses of fresh garlic or allicin-rich products should not be taken with antiplatelet drugs (speculative).24 Herbal Reality points out the caution rests on single case reports.9 The aged extract trial that found no effect was funded by the extract's maker. Food amounts are not a concern. For supplements or several raw cloves a day, involve the prescriber who monitors your INR.
- Blood pressure medication. Trials report a modest drop with aged extract, so an additive effect is possible. One case report involves lisinopril.9,14 Monitor and tell your prescriber.
- Insulin and diabetes medication. Brinker advises caution with large doses in type 1 diabetes and notes insulin doses may need adjusting (speculative). The basis is rapid glucose-lowering in rats and rabbits and a human study in which 800 mg of garlic powder daily for over 4 weeks reduced blood glucose by 11.6 percent.24 Traditional Chinese sources give the same advice. Low risk at food amounts; monitor with supplements.
- Chlorzoxazone and other CYP2E1 drugs. Garlic oil at 500 mg three times daily for 28 days slowed the breakdown of chlorzoxazone, a muscle relaxant, in 12 volunteers, with more sedation reported; the enzymes CYP1A2, 2D6, and 3A4 were unaffected (human study). Ten ml of aged garlic extract daily for 12 weeks did not change acetaminophen metabolism by the same enzyme in 16 people, which Brinker attributes to the aged extract's near absence of diallyl sulfide.24 Garlic oil and fresh garlic are the forms to watch here.
- Cholesterol-lowering drugs. Brinker lists a possible additive effect (speculative) from a meta-analysis of 1 to 3 month trials, then cites the 6-month Gardner trial that found no lipid effect at all.13,24 Food amounts are not a concern.
Surgery
The EMA advises avoiding garlic for 7 days before surgery because of post-operative bleeding risk; Pole and Herbal Reality say 10 days.6,8,9 Brinker records heavy pre-surgical consumption leading to longer clotting time or reduced platelet aggregation (human case reports), and one spontaneous spinal epidural hematoma in a person eating 4 cloves (2 g) daily (human case report). He gives both the 7-day and 10-day windows and grades each speculative.24 One practical detail from his in vitro data: 3 minutes of boiling or oven heat at 200°C left garlic's antiplatelet activity intact, 6 minutes suppressed it for whole cloves, and 10 minutes abolished it for crushed garlic, so well-cooked garlic is the least concerning form before surgery.24 Tell your surgical team about any garlic supplement, and follow their window.
Digestive and mucosal irritation
- Stomach inflammation. Brinker advises avoiding garlic with acute or chronic stomach inflammation, or marked irritation of other mucous membranes (empirical), because concentrated garlic disulfides cause gastroenteritis (empirical).24 High doses can cause burning in the mouth, nausea, gas, and diarrhea, and King's recorded vomiting and purging from large doses.1,6,12 Take supplements with food.
- Acid reflux. Brinker advises avoiding garlic in reflux (speculative), reasoning from a human study in which aromatic oils like peppermint relaxed the lower esophageal sphincter. The sphincter data come from peppermint, so this is his inference rather than a garlic finding.24 Pole's pitta caution points the same way.8
Skin and mucous membranes
- Raw garlic on skin causes chemical burns. Thirty-nine published cases from age 3 months to 80, nearly all from crushed garlic held under a bandage or cloth for hours. Some needed skin grafts.20 Brinker describes a 17-month-old burned on the tops of both feet by a fresh garlic poultice left on for 8 hours with no oil, who later patch-tested negative for garlic allergy (human case report), which shows the injury is chemical rather than allergic.24 King's noted the same in 1898: the oil causes violent pain, redness, and often blistering on contact.1 Do not tape garlic to skin, and do not apply it to a child.
- Allergy and contact dermatitis. Brinker records rare allergic hypersensitivity after frequent contact, typically in kitchen and farm workers, and blistering from the juice (empirical).24 The EMA lists contact dermatitis, conjunctivitis, rhinitis, and, rarely, bronchospasm.6,12
Thyroid
Brinker advises against garlic in low thyroid function (speculative): fresh garlic homogenate and its vinyldithiin components lowered T3, T4, and TSH within 6 to 12 hours in rats, and he adds that regular use of purified constituents might reduce iodine uptake (speculative).24 No human data exist. Food amounts are not a concern.
Pregnancy, nursing, and children
- Pregnancy. Culinary amounts are fine. The EMA does not recommend medicinal use for lack of safety data, and Pole advises against medicinal doses as too stimulating.6,8 Brinker advises avoiding large amounts in early pregnancy (speculative) on the basis of a traditional emmenagogue effect (empirical) and uterine stimulation in laboratory and animal work, and against prolonged high doses of fresh garlic or high-allicin products at any stage because of bleeding risk (speculative).24 Bensky advises against garlic enemas in pregnancy.10
- Nursing. Pole considers garlic fine during lactation, while the EMA does not recommend medicinal use for lack of data.6,8 The food-level research is reassuring: garlic flavor reached breast milk and peaked about two hours after eating, and infants nursed longer rather than pulling away, with no harm reported.21,22 Food amounts have a long history; keep supplements for after weaning unless your provider agrees otherwise.
- Children. The EMA does not recommend garlic as a medicine under 18 for cardiovascular use or under 12 for colds, for lack of data.6 Children appear in the burn reports more often than adults. Food amounts are fine; skip raw garlic on the skin entirely.
Pets
Garlic, onions, leeks, and chives damage red blood cells in dogs and cats and can cause Heinz body hemolytic anemia, sometimes days after the meal. Garlic is several times more potent than onion by weight, and cats are more sensitive than dogs.23 Do not give garlic to pets as a supplement or flea remedy without a veterinarian's guidance.
Constitutional cautions
- Ayurveda: increases pitta. Avoid medicinal doses with hyperacidity, ulcers, reflux, and heat-driven high blood pressure.8
- Traditional Chinese Medicine: contraindicated in yin deficiency with heat and in heat affecting the eyes, mouth, throat, or gums.10
- Cook: large amounts or prolonged external use produce hot skin, flushing, and headache.4
- Rat studies found reduced sperm production and testosterone at roughly twice the maximum human dose; the EMA lists this as an unresolved preclinical finding.6 No human data exist.
Where garlic has been studied alongside medications
Brinker's entry also records combinations in which garlic preparations were studied with a drug for a supportive effect, in people or in laboratory work. These are research findings, not recommendations, and every one of them involved a prescriber managing the drug.24
- Aged garlic extract at 4 ml daily for one year slowed coronary plaque calcification in patients with coronary artery disease already on statins and aspirin (human clinical trial), and 2.4 g daily for two weeks improved brachial artery dilation in men with coronary disease on the same drugs (randomized crossover).
- A topical garlic gel applied twice daily for 3 months alongside 0.1 percent betamethasone cream produced better regrowth in 20 people with patchy hair loss than the steroid alone in 20 others (human clinical study). This is the one topical garlic use on the page with a favorable human trial, and it used a gel, not raw cloves.
- In animals and cells, garlic or its sulfur compounds reduced organ damage from acetaminophen, gentamicin, methotrexate, doxorubicin, and isoprenaline, and allicin lowered the amount of vancomycin needed against resistant Enterococcus while the essential oil boosted ketoconazole against ringworm fungi (animal and in vitro). None of this has been tested in people.
Frequently Asked Questions
Is garlic good for you?
In food amounts it supports digestion, circulation, and the lungs, and every major herbal tradition uses it. The main cautions apply to supplements in people on blood thinners or HIV medication, to anyone with surgery scheduled, and to raw garlic on skin.
Does garlic lower cholesterol?
The largest independent trial, 192 adults over six months, found no change in LDL from raw garlic or two supplements at a clove a day. Some smaller and shorter trials, many supplement-funded, reported modest drops in people with elevated cholesterol. Treat garlic as a supportive food, and do not adjust cholesterol medication around it.
Does garlic lower blood pressure?
A pooled analysis of 20 trials found systolic pressure about 5 mmHg lower with garlic, and closer to 8 or 9 mmHg in people who started high. Much of that research used one commercial aged garlic extract and was funded by its maker. The effect is modest and short-term.
Does garlic thin the blood?
Human trials show that garlic tablets and fresh garlic reduce platelet clumping and clotting signals over weeks, and a few case reports describe bleeding problems in people on warfarin who added garlic products. Two human trials that added garlic to warfarin found no change in clotting measures. Food amounts are not a concern. Supplements, or more than 5 g of fresh garlic a day, deserve a conversation with whoever manages your blood thinner.
Can I put raw garlic on my skin?
No. Crushed garlic held against skin under a bandage causes chemical burns, sometimes deep ones, and children are the most common patients in the published cases. A diluted garlic-infused oil is the traditional external form.
Does cooking destroy garlic's benefits?
Heat destroys the enzyme that makes allicin, so whole cloves dropped into a hot pan produce little of it. Crushing the garlic and letting it sit about 10 minutes before cooking lets allicin form first. The water-soluble alliin and the fructans survive cooking either way, and laboratory work found about 3 minutes of heat leaves the antiplatelet activity intact while 10 minutes removes it.
Can dogs eat garlic?
No. Garlic and its relatives damage red blood cells in dogs and cats and can cause anemia that shows up days later. Cats are more sensitive than dogs. Skip it as a supplement or flea remedy unless your veterinarian directs otherwise.
How do you make garlic honey?
Peel and lightly crush cloves, cover them with raw honey in a clean jar, and let it sit a few weeks, turning the jar now and then. Refrigerate once the cloves release liquid. Herbal Reality recommends it as the easiest way to take raw garlic for people who find the bite too much.
Sources
- Felter HW, Lloyd JU. Allium (U.S.P.), Garlic. King's American Dispensatory, 1898. Public domain, hosted at Henriette's Herbal.
- Felter HW, Lloyd JU. Syrupus Allii (U.S.P.), Syrup of Garlic. King's American Dispensatory, 1898.
- Felter HW. Allium Sativum. The Eclectic Materia Medica, Pharmacology and Therapeutics, 1922.
- Cook WH. Allium Sativum, Garlic. The Physiomedical Dispensatory, 1869.
- German Commission E monograph, Allii sativi bulbus, 1988. In: Blumenthal M, ed. The Complete German Commission E Monographs. American Botanical Council, 1998.
- European Medicines Agency, Committee on Herbal Medicinal Products. European Union herbal monograph on Allium sativum L., bulbus. EMA/HMPC/7685/2013, adopted 18 July 2017.
- European Medicines Agency, Committee on Herbal Medicinal Products. Assessment report on Allium sativum L., bulbus. 2017. Summarizes ESCOP, British Herbal Pharmacopoeia, and WHO positions and the constituent chemistry.
- Pole S. Ayurvedic Medicine: The Principles of Traditional Practice. (affiliate link) Pole is a co-founder of Pukka Herbs, a tea company.
- Herbal Reality. Garlic (Allium sativum) monograph. Last reviewed June 2023. Herbal Reality is a UK charity founded by Sebastian Pole of Pukka Herbs; it is herbalist-written and does not sell products.
- Bensky D, Clavey S, Stöger E. Chinese Herbal Medicine: Materia Medica, 3rd edition. Eastland Press, 2004. Da Suan entry summarized here; the book itself is the source.
- Hobbs C. Herbs for Infectious Diseases. Lecture notes summarizing Chinese clinical reports on Da Suan.
- Hoffmann D. Medical Herbalism: The Science and Practice of Herbal Medicine. Healing Arts Press, 2003. (affiliate link)
- Gardner CD, Lawson LD, Block E, et al. Effect of raw garlic vs commercial garlic supplements on plasma lipid concentrations in adults with moderate hypercholesterolemia: a randomized clinical trial. Archives of Internal Medicine. 2007;167(4):346-353. DOI: 10.1001/archinte.167.4.346. NIH-funded.
- Ried K. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol, and stimulates immunity: an updated meta-analysis and review. Journal of Nutrition. 2016;146(2):389S-396S. Read at the journal. Published in a supplement from a Wakunaga-sponsored symposium; the author's own trials were funded by Wakunaga.
- Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database of Systematic Reviews. 2014;(11):CD006206. DOI: 10.1002/14651858.CD006206.pub4.
- Josling P. Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey. Advances in Therapy. 2001;18(4):189-193. DOI: 10.1007/BF02850113. Author affiliated with the Garlic Centre, UK, a supplier of allicin products.
- Nantz MP, Rowe CA, Muller CE, et al. Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. Clinical Nutrition. 2012;31(3):337-344. DOI: 10.1016/j.clnu.2011.11.019. Funded by Wakunaga of America.
- Piscitelli SC, Burstein AH, Welden N, Gallicano KD, Falloon J. The effect of garlic supplements on the pharmacokinetics of saquinavir. Clinical Infectious Diseases. 2002;34(2):234-238. DOI: 10.1086/324351. NIH Clinical Center.
- Macan H, Uykimpang R, Alconcel M, et al. Aged garlic extract may be safe for patients on warfarin therapy. Journal of Nutrition. 2006;136(3 Suppl):793S-795S. DOI: 10.1093/jn/136.3.793S. Co-authored by Wakunaga staff.
- Garlic burn injuries: a systematic review of reported cases. American Journal of Emergency Medicine. 2021.
- Drugs and Lactation Database (LactMed). Garlic. National Institute of Child Health and Human Development.
- Mennella JA, Beauchamp GK. Maternal diet alters the sensory qualities of human milk and the nursling's behavior. Pediatrics. 1991;88(4):737-744. Read at the journal. NIH-funded.
- Merck Veterinary Manual. Garlic and Onion (Allium spp) Toxicosis in Animals. Merck is a pharmaceutical company; the manual is a clinical reference and does not sell the products discussed here.
- Brinker F. Herbal Contraindications and Drug Interactions: Plus Herbal Adjuncts with Medicines, 4th edition. Eclectic Medical Publications, 2010. Garlic entry, pages 161 to 166. Brinker grades each statement as empirical, speculative, or by study type; those grades are carried in the text above.
This monograph is updated as new research and sources become available.
Ivy Ham
I'm Ivy Ham, a clinical herbalist dedicated to blending traditional healing wisdom with modern science, and revealing how nature's remedies can enhance everyday wellness. Through my blog, I share insights on herbal solutions, nutrition, and holistic practices to guide you toward a more balanced, vibrant life.
Certified clinical herbalist · Missoula, Montana · Read more about Ivy
Safety and Cautions
Not medical advice. Herbs contain active compounds that can interact with medications and health conditions. Garlic at food amounts has thousands of years of safe use. The cautions below apply to medicinal amounts, supplements, and raw garlic on skin. Talk with your healthcare provider or pharmacist before using it beyond cooking if any of these apply to you.
Medication interactions
- Saquinavir and ritonavir (HIV medication). The EMA contraindicates garlic preparations with these drugs because garlic caplets cut saquinavir blood levels by half in a human trial, with a risk of treatment failure and viral resistance.6,18 Anyone on antiretroviral therapy should keep garlic to food amounts and check with their prescriber.
- Blood thinners and antiplatelet drugs. The sources disagree. The EMA advises caution because garlic may lengthen bleeding time, and case reports describe raised INR in people on warfarin who added garlic products.6,9 Hoffmann and Pole both carry the caution.8,12 Against that, a trial of aged garlic extract in 48 patients on warfarin found no change in INR or bleeding, and a separate healthy-volunteer study found the same.19 Herbal Reality points out the caution rests on single case reports.9 The trial that found no effect was funded by the extract's maker. Food amounts are not a concern. For supplements, involve the prescriber who monitors your INR.
- Blood pressure medication. Trials report a modest drop with aged extract, so an additive effect is possible. One case report involves lisinopril.9,14 Monitor and tell your prescriber.
- Diabetes medication. Traditional Chinese sources advise monitoring with insulin and oral glucose-lowering drugs. Human evidence for a blood sugar effect is thin. Low risk at food amounts.
Surgery
The EMA advises avoiding garlic for 7 days before surgery because of post-operative bleeding risk; Pole and Herbal Reality say 10 days.6,8,9 Tell your surgical team about any garlic supplement, and follow their window.
Skin and mucous membranes
- Raw garlic on skin causes chemical burns. Thirty-nine published cases from age 3 months to 80, nearly all from crushed garlic held under a bandage or cloth for hours. Some needed skin grafts.20 King's noted the same in 1898: the oil causes violent pain, redness, and often blistering on contact.1 Do not tape garlic to skin, and do not apply it to a child.
- Contact dermatitis from handling garlic is documented in food workers, and the EMA lists allergic reactions including conjunctivitis, rhinitis, and, rarely, bronchospasm.6,12
- Digestive irritation. High doses can cause burning in the mouth, nausea, gas, and diarrhea, and King's recorded vomiting and purging from large doses.1,6,12 Take supplements with food.
Pregnancy, nursing, and children
- Pregnancy. Culinary amounts are fine. The EMA does not recommend medicinal use for lack of safety data, and Pole advises against medicinal doses as too stimulating.6,8 Bensky advises against garlic enemas in pregnancy.10
- Nursing. Pole considers garlic fine during lactation, while the EMA does not recommend medicinal use for lack of data.6,8 The food-level research is reassuring: garlic flavor reached breast milk and peaked about two hours after eating, and infants nursed longer rather than pulling away, with no harm reported.21,22 Food amounts have a long history; keep supplements for after weaning unless your provider agrees otherwise.
- Children. The EMA does not recommend garlic as a medicine under 18 for cardiovascular use or under 12 for colds, for lack of data.6 Children appear in the burn reports more often than adults. Food amounts are fine; skip raw garlic on the skin entirely.
Pets
Garlic, onions, leeks, and chives damage red blood cells in dogs and cats and can cause Heinz body hemolytic anemia, sometimes days after the meal. Garlic is several times more potent than onion by weight, and cats are more sensitive than dogs.23 Do not give garlic to pets as a supplement or flea remedy without a veterinarian's guidance.
Constitutional cautions
- Ayurveda: increases pitta. Avoid medicinal doses with hyperacidity, ulcers, reflux, and heat-driven high blood pressure.8
- Traditional Chinese Medicine: contraindicated in yin deficiency with heat and in heat affecting the eyes, mouth, throat, or gums.10
- Cook: large amounts or prolonged external use produce hot skin, flushing, and headache.4
- Rat studies found reduced sperm production and testosterone at roughly twice the maximum human dose; the EMA lists this as an unresolved preclinical finding.6 No human data exist.
Frequently Asked Questions
Is garlic good for you?
In food amounts it supports digestion, circulation, and the lungs, and every major herbal tradition uses it. The main cautions apply to supplements in people on blood thinners or HIV medication, to anyone with surgery scheduled, and to raw garlic on skin.
Does garlic lower cholesterol?
The largest independent trial, 192 adults over six months, found no change in LDL from raw garlic or two supplements at a clove a day. Some smaller and shorter trials, many supplement-funded, reported modest drops in people with elevated cholesterol. Treat garlic as a supportive food, and do not adjust cholesterol medication around it.
Does garlic lower blood pressure?
A pooled analysis of 20 trials found systolic pressure about 5 mmHg lower with garlic, and closer to 8 or 9 mmHg in people who started high. Much of that research used one commercial aged garlic extract and was funded by its maker. The effect is modest and short-term.
Does garlic thin the blood?
Garlic compounds slow platelet clumping in laboratory work, and a few case reports describe bleeding problems in people on warfarin who added garlic products. Two human trials that added garlic to warfarin found no change in clotting measures. Food amounts are not a concern. Supplements deserve a conversation with whoever manages your blood thinner.
Can I put raw garlic on my skin?
No. Crushed garlic held against skin under a bandage causes chemical burns, sometimes deep ones, and children are the most common patients in the published cases. A diluted garlic-infused oil is the traditional external form.
Does cooking destroy garlic's benefits?
Heat destroys the enzyme that makes allicin, so whole cloves dropped into a hot pan produce little of it. Crushing the garlic and letting it sit about 10 minutes before cooking lets allicin form first. The water-soluble alliin and the fructans survive cooking either way.
Can dogs eat garlic?
No. Garlic and its relatives damage red blood cells in dogs and cats and can cause anemia that shows up days later. Cats are more sensitive than dogs. Skip it as a supplement or flea remedy unless your veterinarian directs otherwise.
How do you make garlic honey?
Peel and lightly crush cloves, cover them with raw honey in a clean jar, and let it sit a few weeks, turning the jar now and then. Refrigerate once the cloves release liquid. Herbal Reality recommends it as the easiest way to take raw garlic for people who find the bite too much.
Sources
- Felter HW, Lloyd JU. Allium (U.S.P.), Garlic. King's American Dispensatory, 1898. Public domain, hosted at Henriette's Herbal.
- Felter HW, Lloyd JU. Syrupus Allii (U.S.P.), Syrup of Garlic. King's American Dispensatory, 1898.
- Felter HW. Allium Sativum. The Eclectic Materia Medica, Pharmacology and Therapeutics, 1922.
- Cook WH. Allium Sativum, Garlic. The Physiomedical Dispensatory, 1869.
- German Commission E monograph, Allii sativi bulbus, 1988. In: Blumenthal M, ed. The Complete German Commission E Monographs. American Botanical Council, 1998.
- European Medicines Agency, Committee on Herbal Medicinal Products. European Union herbal monograph on Allium sativum L., bulbus. EMA/HMPC/7685/2013, adopted 18 July 2017.
- European Medicines Agency, Committee on Herbal Medicinal Products. Assessment report on Allium sativum L., bulbus. 2017. Summarizes ESCOP, British Herbal Pharmacopoeia, and WHO positions and the constituent chemistry.
- Pole S. Ayurvedic Medicine: The Principles of Traditional Practice. (affiliate link) Pole is a co-founder of Pukka Herbs, a tea company.
- Herbal Reality. Garlic (Allium sativum) monograph. Last reviewed June 2023. Herbal Reality is a UK charity founded by Sebastian Pole of Pukka Herbs; it is herbalist-written and does not sell products.
- Bensky D, Clavey S, Stöger E. Chinese Herbal Medicine: Materia Medica, 3rd edition. Eastland Press, 2004. Da Suan entry summarized here; the book itself is the source.
- Hobbs C. Herbs for Infectious Diseases. Lecture notes summarizing Chinese clinical reports on Da Suan.
- Hoffmann D. Medical Herbalism: The Science and Practice of Herbal Medicine. Healing Arts Press, 2003. (affiliate link)
- Gardner CD, Lawson LD, Block E, et al. Effect of raw garlic vs commercial garlic supplements on plasma lipid concentrations in adults with moderate hypercholesterolemia: a randomized clinical trial. Archives of Internal Medicine. 2007;167(4):346-353. DOI: 10.1001/archinte.167.4.346. NIH-funded.
- Ried K. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol, and stimulates immunity: an updated meta-analysis and review. Journal of Nutrition. 2016;146(2):389S-396S. Read at the journal. Published in a supplement from a Wakunaga-sponsored symposium; the author's own trials were funded by Wakunaga.
- Lissiman E, Bhasale AL, Cohen M. Garlic for the common cold. Cochrane Database of Systematic Reviews. 2014;(11):CD006206. DOI: 10.1002/14651858.CD006206.pub4.
- Josling P. Preventing the common cold with a garlic supplement: a double-blind, placebo-controlled survey. Advances in Therapy. 2001;18(4):189-193. DOI: 10.1007/BF02850113. Author affiliated with the Garlic Centre, UK, a supplier of allicin products.
- Nantz MP, Rowe CA, Muller CE, et al. Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: a randomized, double-blind, placebo-controlled nutrition intervention. Clinical Nutrition. 2012;31(3):337-344. DOI: 10.1016/j.clnu.2011.11.019. Funded by Wakunaga of America.
- Piscitelli SC, Burstein AH, Welden N, Gallicano KD, Falloon J. The effect of garlic supplements on the pharmacokinetics of saquinavir. Clinical Infectious Diseases. 2002;34(2):234-238. DOI: 10.1086/324351. NIH Clinical Center.
- Macan H, Uykimpang R, Alconcel M, et al. Aged garlic extract may be safe for patients on warfarin therapy. Journal of Nutrition. 2006;136(3 Suppl):793S-795S. DOI: 10.1093/jn/136.3.793S. Co-authored by Wakunaga staff.
- Garlic burn injuries: a systematic review of reported cases. American Journal of Emergency Medicine. 2021.
- Drugs and Lactation Database (LactMed). Garlic. National Institute of Child Health and Human Development.
- Mennella JA, Beauchamp GK. Maternal diet alters the sensory qualities of human milk and the nursling's behavior. Pediatrics. 1991;88(4):737-744. Read at the journal. NIH-funded.
- Merck Veterinary Manual. Garlic and Onion (Allium spp) Toxicosis in Animals. Merck is a pharmaceutical company; the manual is a clinical reference and does not sell the products discussed here.
This monograph is updated as new research and sources become available.
Ivy Ham
I'm Ivy Ham, a clinical herbalist dedicated to blending traditional healing wisdom with modern science, and revealing how nature's remedies can enhance everyday wellness. Through my blog, I share insights on herbal solutions, nutrition, and holistic practices to guide you toward a more balanced, vibrant life.
Certified clinical herbalist · Missoula, Montana · Read more about Ivy