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Ayurveda · Traditional Chinese medicine · Western herbalism

GarlicAllium sativum

Kitchen bulb sold as capsules and extract. For gut infections the human data are small pilots and an add-on meta-analysis of allicin (93% vs 84% H. pylori eradication).

Botanical name
Allium sativum
Part used
bulb (the cloves)
Also called
Sanskrit Lasuna, Rasona; Hindi Lehsun; pinyin Da suan (大蒜); Aged garlic extract, Allicin (the compound formed when a clove is crushed)
Used in
Ayurveda, Traditional Chinese medicine, Western herbalism
Taken for
Antimicrobial use, Indigestion
Sold as
capsules, tablets, powder, extract, fresh

What garlic is

Garlic is the bulb of Allium sativum, a close relative of onion and leek, made up of a head of cloves. Crushing or chopping a clove lets an enzyme turn alliin into allicin, the sulfur compound responsible for the smell and for most of the laboratory antimicrobial work. Allicin is unstable, so supplements differ a great deal: dried powder, aged garlic extract, steam-distilled oil, and enteric-coated tablets designed to release allicin in the intestine all appear on shelves.

That variety matters for gut claims. A raw clove, a capsule of powder and an aged extract do not contain the same compounds, and trials of one cannot be transferred to another. Garlic is also one of the highest-fructan vegetables measured. Muir and colleagues found garlic, artichoke, shallots, leek bulb and onions at the top of the list, with fructan contents from 1.2 to 17.4 g per 100 g of fresh weight across the group, and the authors note that fructans can cause gastrointestinal symptoms in some individuals.

In gut supplements garlic appears in antimicrobial, parasite-cleanse and microbiome blends, usually for its allicin.

What the traditions use it for

Ayurveda (about Ayurveda)

Lasuna is the Sanskrit name for garlic. Bayan and colleagues report that ancient Indian medicine used garlic to aid respiration and digestion and to treat leprosy and parasitic infestation. We did not find a readable source that gives the Ayurvedic classification of its taste and effect on digestion, so we do not state one.

Traditional Chinese medicine (about TCM)

Chinese materia medica lists garlic as da suan. Bayan and colleagues note that ancient Chinese medicine used garlic to aid digestion and to treat parasitic infestation. The tradition’s own classification of garlic was not available in the sources we could read, so we do not describe it.

Western herbalism

Garlic is documented from the Avesta, from ancient Sumer and Egypt, and from ancient Greece, where Bayan and colleagues report it was fed to the first Olympic athletes for stamina. The EMA herbal committee’s monograph lists only two traditional uses: an adjuvant for the prevention of atherosclerosis and relief of common cold symptoms. It does not list a gut indication.

The constituents

Sulfur compounds define garlic: alliin, which turns into allicin when the clove is crushed, and in oils and aged extracts, allyl sulfides and S-allylcysteine. Ankri and Mirelman reviewed laboratory work showing that pure allicin inhibits a wide range of bacteria, Candida albicans, and intestinal protozoa including Entamoeba histolytica and Giardia lamblia in a dish. Garlic also contains fructans, the fermentable carbohydrates measured by Muir and colleagues. All of the antimicrobial findings here are test-tube findings, and allicin breaks down quickly, so what reaches the gut from a capsule or a clove is a separate question that the cited laboratory work does not answer.

The human evidence

For Helicobacter pylori, Si and colleagues pooled 8 randomized trials with 867 people that added allicin to standard eradication therapy. Eradication was 93.33 percent (406 of 435) with allicin and 83.56 percent (361 of 432) without (odds ratio 2.75, 95 percent CI 1.74 to 4.35), and ulcer healing was also higher. The authors graded the quality of the evidence very low to low and urged caution. The studies tested allicin as an add-on to antibiotics, not garlic on its own.

Garlic alone has been tested in pilots. McNulty and colleagues gave 4 mg garlic oil capsules four times a day for 14 days to dyspeptic people with H. pylori and found no eradication, no suppression and no symptom improvement in the 5 who completed it. Zardast and colleagues had 15 patients eat 3 g of raw garlic twice a day for 3 days and saw a fall in breath-test readings, with no separate control group.

For parasites, Soffar and Mokhtar gave crude extract or capsules for 3 days to 10 children with Hymenolepis nana and 26 with Giardia lamblia and reported it efficient and safe, though the abstract gives no cure rates.

For stomach cancer, the Shandong Intervention Trial randomized 3,365 people; after 22 years, garlic supplements were linked to a hazard ratio of 0.66 (0.43 to 1.00) for gastric cancer death, while incidence was not significantly lower (odds ratio 0.81, 0.57 to 1.13). A meta-analysis of 19 case-control and 2 cohort studies found an odds ratio of 0.54 for high Allium vegetable intake, but these are observational. The NCCIH states that eating garlic does not appear to reduce stomach cancer risk.

We found no placebo-controlled trial of garlic alone for parasites or for bacterial overgrowth.

StudyDoseWhat it found
Meta-analysis of 8 randomized trials, 867 people with H. pylori PMID 31660038Allicin added to standard eradication therapyEradication 93.33% with allicin versus 83.56% without (OR 2.75, 95% CI 1.74 to 4.35); evidence graded low to very low
Pilot study, dyspeptic people with H. pylori (5 completed) PMID 116839294 mg garlic oil capsule four times daily for 14 daysNo eradication, no suppression and no symptom improvement
Pre-post study, 15 patients with H. pylori, no separate control group PMID 277614183 g raw garlic twice daily for 3 daysUrease breath test readings significantly lower after garlic
Trial in 10 children with H. nana and 26 with Giardia lamblia PMID 18750775 ml crude extract in 100 ml water twice daily, or 2 capsules (0.6 mg) twice daily, 3 daysAuthors reported it efficient and safe; abstract gives no cure rates
Shandong Intervention Trial, 3,365 people, follow-up 22 years PMID 31511230Garlic extract and oil for about 7 yearsGastric cancer death HR 0.66 (0.43 to 1.00); incidence OR 0.81 (0.57 to 1.13), not significant

Doses, in trials and in practice

Trials used very different forms: 4 mg garlic oil capsules four times daily for 14 days, 3 g of raw garlic twice daily for 3 days, and allicin added to antibiotic regimens. The EMA monograph for the traditional uses lists powdered garlic at 300 to 750 mg per dose, 900 to 1,380 mg a day in 3 to 5 divided doses, and 100 to 400 mg a day of dry extract for the cold indication. Raw cloves as food are the oldest preparation. No gut-specific dose has been established.

The amounts above are what trials and pharmacopoeias record, not a dose for you; your medicines and conditions change the answer, and a clinician or pharmacist who knows them is the person to ask.

What is known about safety

The NCCIH reports that oral garlic has been used safely in studies lasting up to 7 years, with breath and body odor, abdominal pain, gas and nausea as the usual side effects and allergic reactions in some people. The EMA monograph also lists bloating, fullness and loss of appetite, plus headache, dizziness, sweating and bleeding. It advises stopping garlic 7 days before surgery because of bleeding risk, states that safety in pregnancy and breastfeeding has not been established, and the NCCIH says amounts above food levels may not be safe in pregnancy. Raw garlic on the skin can cause burns. As a high-fructan food it can aggravate symptoms in some people with irritable bowel syndrome.

Where it meets prescription medicines

Saquinavir: in 10 healthy volunteers taking garlic caplets, the drug’s exposure fell by 51 percent, its trough by 49 percent and its peak by 54 percent; the EMA monograph contraindicates garlic with saquinavir and ritonavir. Anticoagulant and antiplatelet drugs: the EMA states garlic preparations should be used with caution because they may lengthen bleeding time, and the NCCIH says garlic supplements may increase bleeding risk.

Medicines the site’s own interaction rules flag with garlic

The quiz applies these rules when someone names a medicine. They come from published interaction references and are a reason to ask a pharmacist, not a diagnosis:

Catalog entries that list garlic

If you want garlic in a product rather than as a loose herb, these are the entries that carry it, with the label amounts and the reviews read.

Emma Relief Daily Digestive Supplement 4 out of 5 from 11,119 ratings from Amazon · $2.00 a day Grow Young Fitness Daily Probiotic + Prebiotic Fiber 4.9 out of 5 from 1,863 ratings from growyoungshop.com · $2.00 a day Renew Life PARA SMART Cleansing Formula, 15-Day Program 4.2 out of 5 from 1,398 ratings from Amazon · ~$2.04 a day across the full 15-day program Biocidin Botanicals Biocidin Broad-Spectrum Liquid Formula 4.5 out of 5 from 1,079 ratings from Amazon · ~$1.41 per day at the full 15-drop dose

Which product, for your symptoms?

The quiz takes about three minutes, asks what you have tried and which medicines you take, and shows the products whose trials and labels fit, with the reasons.

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Herbs that sit beside it

Western Oregano Origanum vulgare Ayurvedic / TCM / Western Clove Syzygium aromaticum TCM / Western Berberine Berberis, Hydrastis, Coptis and Mahonia species (source plants) Western Black walnut Juglans nigra

Questions people ask

Does garlic kill H. pylori?

Allicin added to standard antibiotic therapy raised eradication from 83.56 to 93.33 percent in a pooling of 8 trials, though the authors graded the evidence low. Garlic oil capsules alone did not eradicate or suppress H. pylori in a pilot of 5 people.

Is there a trial showing garlic clears parasites?

A 1991 Egyptian trial gave extract or capsules for 3 days to 10 children with Hymenolepis nana and 26 with Giardia lamblia and reported it efficient and safe, but the abstract gives no cure rates. We found no placebo-controlled trial.

Does garlic prevent stomach cancer?

Observational studies link high Allium vegetable intake to lower risk (odds ratio 0.54 in one pooling). In the Shandong trial, garlic supplements were linked to fewer gastric cancer deaths after 22 years (HR 0.66) but not significantly fewer cases. The NCCIH states that eating garlic does not appear to reduce risk.

Why does garlic cause gas in some people?

Garlic is among the highest-fructan foods measured, with fructan contents up to 17.4 g per 100 g of fresh weight across the top group of vegetables. Fructans are fermented by gut bacteria, and the EMA monograph lists bloating and flatulence among garlic’s side effects.

Does garlic interact with medicines?

Yes, two are documented. Garlic caplets lowered saquinavir exposure by 51 percent in healthy volunteers, and the EMA contraindicates the combination. It may also lengthen bleeding time, so caution applies with anticoagulants and antiplatelet drugs.

Sources