Garlic
Garlic supplements are studied for cholesterol, blood pressure and blood sugar. NCCIH says they may lower these to a small extent (with only limited evidence for blood pressure), but MSK says studies on cholesterol and blood pressure are mixed. Evidence on cancer and immune support is limited or uncertain.
Garlic supplements are studied for cholesterol, blood pressure and blood sugar. NCCIH says garlic supplements may reduce cholesterol and, in people with diabetes, blood sugar to a small extent, and that limited evidence suggests they may reduce blood pressure to a small extent, while MSK says studies on cholesterol and blood pressure are mixed. A 2022 review identified only two studies that suggest a possible benefit for the immune system.
Where to get it
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Traditional & historical use
Garlic has been used medicinally for thousands of years in ancient Egypt, Greece, Rome, India, and China. Historical uses include infection, wound treatment, digestive problems, and heart conditions. NCCIH notes garlic has been promoted to prevent colds and cardiovascular disease.
Active compounds & mechanisms
Key compounds: allicin, alliin, ajoene, diallyl disulfide, diallyl trisulfide, s-allylcysteine (SAC), flavonoids, saponins
When raw garlic is crushed or chopped, the enzyme alliinase converts alliin to allicin, the primary bioactive compound. Allicin has antimicrobial, antifungal and antiviral properties. Allicin also inhibits platelet aggregation and has mild blood-pressure-lowering effects. Aged garlic extract (AGE) is rich in stable organosulfur compounds like s-allylcysteine that survive heat. Heat cooking largely destroys allicin; supplements containing AGE or allicin-standardised powder retain activity.
Research & evidence
Strong support Some support Weak or no supportColours show how well the sources back each point. The reason is next to each one.
Garlic supplements may reduce total cholesterol and low-density lipoprotein (LDL) cholesterol to a small extent.
Limited evidenceSome support. The source hedges (“may” or “associated with”)
Study details
may reduce levels of total cholesterol and low-density lipoprotein (LDL) cholesterol to a small extent
Source: NCCIH, Garlic (Last Updated February 2025), Research Findings View source
Limited evidence suggests that garlic supplements may reduce blood pressure to a small extent.
Limited evidenceSome support. The source hedges (“may” or “associated with”)
Study details
Limited evidence suggests that garlic supplements may reduce blood pressure to a small extent
Source: NCCIH, Garlic (Last Updated February 2025), Research Findings View source
MSK says studies on whether garlic can reduce cholesterol or lower blood pressure are mixed.
Mixed evidenceSome support. Results are mixed
Study details
Studies on whether garlic can reduce cholesterol or lower blood pressure are mixed
Source: MSK About Herbs, Garlic (updated November 18, 2022), Research Findings View source
Garlic supplements may reduce blood sugar to a small extent in people with diabetes.
Limited evidenceSome support. Shown only in certain groups, uses, strains or doses
Study details
Garlic supplements may reduce blood sugar to a small extent in people with diabetes.
Source: NCCIH, Garlic (Last Updated February 2025), Research Findings View source
Consuming garlic does not seem to reduce the risk of stomach cancer.
Not supported by current evidenceWeak or no support. Trials found no clear benefit
Study details
Consuming garlic does not seem to reduce the risk of stomach cancer.
Source: NCCIH, Garlic (Last Updated February 2025), Research Findings View source
It's uncertain whether garlic influences the risk of colorectal cancer.
Limited evidenceSome support. Reviewers rated the certainty low
Study details
It's uncertain whether garlic influences the risk of colorectal cancer.
Source: NCCIH, Garlic (Last Updated February 2025), Research Findings View source
MSK says evidence on whether garlic can reduce the risk of gastric and colorectal cancers is mixed.
Mixed evidenceSome support. Results are mixed
Study details
Evidence on whether garlic can reduce risk of gastric and colorectal cancers is mixed
Source: MSK About Herbs, Garlic (updated November 18, 2022), Research Findings View source
MSK says long-term garlic supplementation was associated with reduced risk of gastric cancer mortality but not incidence.
Limited evidenceSome support. The source hedges (“may” or “associated with”)
Study details
long-term garlic supplementation was associated with reduced risk of gastric cancer mortality but not incidence
Source: MSK About Herbs, Garlic (updated November 18, 2022), Research Findings View source
A 2022 review identified only two studies that suggest a possible benefit for the immune system.
Limited evidenceSome support. Based on one or a few small trials
Study details
A 2022 review identified only two studies that suggest a possible benefit,
Source: NCCIH, Garlic (Last Updated February 2025), Research Findings View source
MSK says data suggest garlic can stimulate the immune system, but it is unclear whether it can treat infections.
Limited evidenceSome support. Reviewers rated the certainty low
Study details
Data suggest garlic can stimulate the immune system, but it is unclear whether it can treat infections
Source: MSK About Herbs, Garlic (updated November 18, 2022), Research Findings View source
MSK says it is unclear whether garlic protects against Helicobacter pylori infection.
Limited evidenceSome support. Reviewers rated the certainty low
Study details
Whether garlic protects against Helicobacter pylori infection is also unclear
Source: MSK About Herbs, Garlic (updated November 18, 2022), Research Findings View source
Dosage
| Form | Amount |
|---|---|
| Any form | Fresh: 2–5 g (about 1–2 cloves) of raw garlic per day; cooking reduces allicin content significantly |
| Capsule | 600–1,200 mg of aged garlic extract (AGE) daily, divided into 2–3 doses; or 500–1,000 mg allicin-standardised garlic powder |
Side effects
Garlic taken by mouth can cause breath and body odour, belly pain, gas and nausea. Garlic supplements may increase the risk of bleeding, so tell your health care providers, and note that MSK advises stopping garlic at least 7 days before surgery. Fresh raw garlic on the skin can cause severe irritation and chemical burns.
Well documented Reported (case reports, anecdotal or one study) None reportedThe circle shows how well documented an effect is, not how serious it is. A rarely reported effect can still be serious, so always read ‘When to stop’.
| Effect | Frequency | When to stop |
|---|---|---|
| Breath and body odourWell documentedListed plainly by NIH, MSK or LiverTox | Not stated | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
| Abdominal pain, flatulence and nauseaWell documentedListed plainly by NIH, MSK or LiverTox | Not stated | Stop and talk to a doctor if you notice any unexpected or concerning symptoms. |
| Increased risk of bleeding (garlic supplements)Well documentedListed plainly by NIH, MSK or LiverTox | Not stated | If you take garlic supplements, make sure to tell your health care providers. MSK advises stopping garlic at least 7 days before surgery. |
| Severe skin irritation and chemical burns (fresh raw garlic used on the skin)Well documentedListed plainly by NIH, MSK or LiverTox | Not stated | MSK says topical use of garlic preparations should be avoided. |
Safety & interactions
Safety
Garlic taken by mouth has been used safely in research studies that lasted as long as 7 years. Taking garlic supplements may increase the risk of bleeding, so tell your health care providers if you take them. Side effects of garlic consumed orally include breath and body odour, abdominal pain, flatulence and nausea. Fresh raw garlic may not be safe when used on the skin, and it can cause severe skin irritation and chemical burns. NCCIH says some herbs and medicines interact in harmful ways, so talk with your health care provider before using garlic or other herbal products.
Contraindications
Garlic may not be safe for use during pregnancy or while breastfeeding, according to NCCIH, which also says little is known about the safety of using garlic on the skin during pregnancy or breastfeeding. MSK says garlic should not be used with anticoagulants (blood thinners) or in patients with platelet dysfunction, and advises stopping garlic at least 7 days before surgery. MSK also says topical use of garlic preparations should be avoided. If you take warfarin, HIV protease inhibitors, cyclosporine, insulin or other blood sugar-lowering drugs, see Drug interactions.
Drug interactions
MSK says garlic may increase the risk of bleeding or bruising when taken with warfarin or other blood thinners. MSK notes that garlic is known to decrease platelet aggregation and potentially elevate INR values, and says it should not be used with anticoagulants or in patients with platelet dysfunction. NCCIH says taking garlic supplements may increase the risk of bleeding and advises telling your health care providers.
MSK reports that in 2 cases of HIV patients who regularly consumed garlic, darunavir became ineffective.
MSK says garlic can reduce the effectiveness of cyclosporine and potentially cause transplant rejection.
MSK says dose adjustments may be required because of the potential blood sugar-lowering effects of garlic supplements. NCCIH says garlic supplements may reduce blood sugar to a small extent in people with diabetes.
MSK says garlic may increase the risk of side effects of drugs broken down by these CYP450 enzymes.
MSK says garlic may reduce the activity of drugs that are P-glycoprotein substrates.
Established: stated plainly by an authoritative source. Documented: supported by case reports or trial data. Theoretical: based on mechanism, animal data, or a cautious listing. Always check with your pharmacist or prescriber.
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