Garlic: Benefits, Dosage, and Safety

What garlic is

Garlic is the edible bulb of Allium sativum, a plant in the onion (Allium) family that has been used in food and for health purposes for thousands of years. As a dietary supplement it is promoted for managing high blood cholesterol, high blood pressure, and blood sugar, and for immune support. It is a food and botanical rather than an essential nutrient, so it has no vitamin or mineral requirement. Its biological activity is generally attributed to organosulfur compounds, including allicin, which forms from the precursor alliin when raw garlic is crushed or chopped.

What it does

• Provides organosulfur compounds (such as allicin) studied for effects on blood lipids
• May modestly affect blood cholesterol and LDL levels in people with high cholesterol, per meta-analyses
• May have a small effect on blood pressure and blood sugar based on limited research
• Used as a culinary flavoring and traditional botanical rather than as a source of an essential nutrient

Intake and dosing

Garlic is not an essential nutrient, so no Recommended Dietary Allowance or Tolerable Upper Intake Level has been set. Doses in studies vary widely. Because supplement doses are not standardised, discuss an appropriate amount with a clinician or pharmacist.

Deficiency and who is at risk

Not applicable. Garlic is a food and botanical, not an essential nutrient, so there is no deficiency state and no Dietary Reference Intake. No deficiency signs are defined by ODS, NCCIH, or the NASEM Dietary Reference Intakes.

Who may need more

• People with high blood cholesterol who choose to try garlic supplements, understanding the effect is small
• People with high blood pressure or diabetes exploring adjuncts, with clinician guidance (evidence is limited)
• Not required by anyone as an essential nutrient

Food sources

Fresh garlic bulbs and cloves, garlic powder, dehydrated garlic, and garlic used as a seasoning. Related Allium vegetables include onions, leeks, and chives.

Forms and absorption

Fresh raw cloves, cooked garlic, dried or powdered garlic in tablets and capsules, aged garlic extract, and garlic oil or liquid extracts. Allicin content varies widely by preparation: crushing raw garlic converts alliin to allicin via the enzyme alliinase, while cooking and some processing can reduce allicin. Enteric-coated tablets are sometimes used to protect the enzyme. Because products are not standardized, the amount of active organosulfur compounds delivered differs across brands and forms.

Safety, excess and interactions

Too much

There is no defined toxicity threshold or Tolerable Upper Intake Level. Garlic taken orally has been used safely in research studies lasting as long as 7 years. Common side effects with oral use include breath and body odor, abdominal pain, flatulence, and nausea, and these are more common with raw garlic. Some people have allergic reactions. Fresh raw garlic applied to the skin can cause severe skin irritation and chemical burns.

Interactions to know

• Anticoagulants (for example warfarin): garlic supplements may increase the risk of bleeding when combined with blood thinners
• Aspirin and antiplatelet medicines: combined use may further affect bleeding risk
• Surgery: garlic supplements may raise bleeding risk around surgical procedures, so disclose use to your surgeon
• Saquinavir (an HIV protease inhibitor): garlic has been reported to reduce blood levels of this drug (per prior NCCIH fact-sheet guidance); discuss any herbal use with your provider as some herbs and medicines interact in harmful ways

How status is measured

Not routinely measured. There is no clinical laboratory marker for garlic status because it is not an essential nutrient.

Regulated as a dietary supplement when marketed for oral use. Unlike drugs, dietary supplements are not approved by the FDA before they are sold; manufacturers and distributors are responsible for evaluating safety and labeling. The FDA can act after marketing if safety concerns arise.

What the evidence supports

We grade the strength of evidence behind each common reason people take garlic, mirroring how the NIH describes it.