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Garlic (Allium sativum) is a food product that can improve immunity and cardiovascular health.

Our evidence-based analysis on garlic features 669 unique references to scientific papers.

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Summary of Garlic

Primary information, health benefits, side effects, usage, and other important details

Garlic (Allium sativum) is a popular vegetable with a variety of medicinal properties.

Taking or eating garlic can benefit cardiovascular health, physical and sexual vitality, cognition, and resistance to infection. It also has anti-aging properties.

Raw or aged garlic reliably reduces total cholesterol and Low-density Lipoprotein (LDL-C), while increasing High-density Lipoprotein (HDL-C). Garlic also provides a variety of anti-cancer properties. Eating garlic daily (10g or more) is associated with a significantly reduced risk of prostate, colon, and stomach cancer. It can also induce fat loss and adrenaline secretion, though in a minor way. Garlic appears to mildly and unreliably reduce triglyceride levels.

Garlic’s main mechanism involves a molecule called alliin. When garlic is physically disturbed through chewing, slicing, or crushing, it releases an alliin metabolite: allicin. Allicin turns into a variety of fat and water soluble sulfur-containing compounds. In fact, these compounds are so volatile, they give off hydrogen sulfide, which is part of garlic’s unmistakable smell and taste. By tapping into the hydrogen sulfide signaling system, garlic relaxes the blood vessels and provides a variety of health benefits. Garlic also uses the hydrogen sulfide signaling system to exert its anti-cancer effects.

Garlic can be taken in several forms: fresh/raw garlic, aged garlic, garlic oil and boiled garlic. Boiled garlic prevents alliin from creating its sulfur-containing metabolites, and garlic oil, while effective as a supplement, has a potentially high level of toxicity. All of the beneficial components of garlic can be found in fresh garlic, which makes aged garlic supplements and fresh garlic the two best ways to supplement garlic. Garlic should be crushed, sliced, or chewed (prior to cooking) in order to ensure maximum allicin production, since allicin is responsible for many of garlic’s beneficial effects.

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How to Take

Recommended dosage, active amounts, other details

Most studies on garlic use a dosage range of 600-1,200mg a day, usually divided into multiple doses. The minimum effective dose for raw garlic is a single segment of a garlic bulb (called a clove), eaten with meals two or three times a day.

Aged garlic is a popular form of garlic to use for supplementation, since it does not have a fresh garlic scent. Garlic supplementation can also be done through food alone, though side-effects will include strong garlic-scented breath.

Microwaving garlic will partially destroy the beneficial components of the vegetable, but grilling and roasting will not damage the bioactives, provided the garlic is sliced or crushed beforehand. Garlic can be toxic if consumed in very high doses, so supplementation should never go beyond 5% of the diet. This results in the following maximum dosages:

  • 17.0 grams for a 150lb person

  • 22.7 grams for a 200lb person

  • 28.4 grams for a 250lb person

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Human Effect Matrix

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The Human Effect Matrix summarizes human studies to tell you what effects Garlic has on your body, how much evidence there is, and how strong these effects are.

Full details are available to Examine members.
Grade Level of Evidence
Robust research conducted with repeated double-blind clinical trials
Multiple studies where at least two are double-blind and placebo controlled
Single double-blind study or multiple cohort studies
Uncontrolled or observational studies only
Level of Evidence
? The amount of high quality evidence. The more evidence, the more we can trust the results.
Outcome Magnitude of effect
? The direction and size of the supplement's impact on each outcome. Some supplements can have an increasing effect, others have a decreasing effect, and others have no effect.
Consistency of research results
? Scientific research does not always agree. HIGH or VERY HIGH means that most of the scientific research agrees.
grade-a Notable Very High See all 14 studies
Garlic supplementation tends to increase HDL cholesterol in persons with cardiovascular disease risk reliably and in the range of 10-15% when looking at individual trials and by 1.49mg/dL (95% CI of 0.19-2.79mg/dL) as assessed by meta-analysis.
grade-a Notable Very High See all 14 studies
There appears to be a reliable and significant reduction in circulating LDL cholesterol in hypercholesterolemic persons with garlic supplementation, and the magnitude of this change tends to be in the range of 10-20% (more potency in those with worse profiles at baseline)
grade-a Notable Very High See all 17 studies
Garlic supplementation or the raw garlic bulb appears to reduce cholesterol (total cholesterol, mostly due to LDL reductions) reliably and in the range of 10-15%
grade-a Minor Very High See all 15 studies
There appears to be quite an unreliable decrease in triglycerides following garlic supplementation. When looking at meta-analyses, there is either a significant but small decrease or a reduction that fails to reach statistical significance.
grade-b Notable High See all 12 studies
Garlic supplementation appears to reduce blood pressure, and the magnitude is quite respectable in persons with hypertension (around 10 points systolic or 8-10%) whereas there is a smaller but present reduction in persons with normal blood pressure.
grade-b - Very High See 2 studies
Although there may theoretically be some benefit with higher doses, currently the available evidence has not found a protective effect with 900mg of raw garlic extract.
grade-b - Very High See all 3 studies
While there are signficant modifications in the subpopulations of white blood cells (ie. which immune cells you have) the overall quantity does not appear significantly affected.
grade-c Strong Very High See 2 studies
The rate (frequency of occurring) of the common cold has twice been found to be reduced by 60-70% in persons who take garlic supplementation daily; this is associated with both allicin and the aged garlic extract, and requires higher doses (2.5g aged extract or 180mg allicin).
grade-c Notable - See study
Following 250mg of garlic oil ingestion for a variable 9-18 months, two thirds of the group given supplementation reversed their status of having hepatopulmonary symptoms (1 person in placebo) and the mortality rate during followup was greatly reduced.
grade-c Notable - See study
The lone human study using a rather high dose of Aged Garlic extract (2.56g) noted an 8-fold increase of this T-cell subpopulation relative to control; thought to be related to the cold fighting properties of garlic
grade-c Minor - See study
There appears to be an increase in adiponectin associated with 1,200mg of aged garlic supplementation despite no other influence on the body of persons with metabolic syndrome.
grade-c Minor Moderate See all 3 studies
There appears to be an increase in glutathione related enzymes in red and white blood cells following ingestion of garlic supplements.
grade-c Minor Very High See 2 studies
There appears to be a reduction in arterial stiffness seen with daily supplementation of garlic when measured over the course of a few years, relative to no garlic ingestion.
grade-c Minor - See study
Stasis has been reported in the growth of arterial plaque over 48 months when people consume 900mg of garlic, but this effect may only be statistically significant for women.
grade-c Minor - See study
Alongside the increase in immune cell activity in otherwise healthy persons is an increase in IFN-y concentrations
grade-c Minor - See study
The length that one is sick for is only modestly reduced with garlic supplementation even at higher doses.
grade-c Minor - See all 3 studies
A reduction in lipid peroxidation in the blood and in red blood cells has been noted in some states of metabolic ailment (aging and hypertension). Not 100% reliable as it wasn't seen in one study on hypercholesterolemia, and no studies in healthy controls.
grade-c Minor - See 2 studies
One study has noted a 20% decrease in the ALT enzyme following garlic supplementation to otherwise healthy controls.
grade-c Minor Moderate See 2 studies
There is an increase in NK cell activity alongside the increase in NK cell content, although it is not sure if there is an inherent increase in NK cell activity if you control for the increase in cell content.
grade-c Minor Very High See 2 studies
There is an increase in NK cell levels seen in both healthy controls as well as cancer patients, and this is thought to be due in part to both immunostimulatory and anti-immunosuppressive effects.
grade-c Minor Moderate See 2 studies
A possible decrease in LDL oxidation rates, although this does not appear to be overly reliable.
grade-c Minor Very High See all 4 studies
Garlic appears to reduce platelet aggregation at the supplemental dose, but not a moderate dietary dose of garlic cloves. The potency is less than ginkgo biloba as a reference.
grade-c Minor - See study
Despite the potent efficacy in reducing the occurrence of sickness, the actual severity of symptoms is only modestly reduced with garlic.
grade-c Minor Very High See 2 studies
Similar to symptoms of sickness in general and the length of sickness, the therapeutic efficacy of garlic appears to be modest at best.
- See 2 studies
Decreases have been noted in inflammatory states (indicative of antiinflammatory effects) and increases seen in healthy persons; suggesting an immunomodulatory effect
grade-c Minor - See study
There appears to be a reduction in the lung infection risks with garlic supplementation.
grade-c - Very High See 2 studies
Minimal studies have directly measured blood flow associated with garlic, and the best evidence currently suggests that basal flow mediated vasodilation is unaffected; there is likely an effect, although most studies indirectly measure blood pressure.
grade-c - - See study
Supplementation of garlic does not appear to significantly reduce fasting blood glucose in persons with metabolic syndrome.
grade-c - - See study
The long study to assesss basal viscosity of the blood has failed to find an interaction with garlic supplementation.
grade-c - Very High See 2 studies
No significant influence on C-reactive protein is noted with supplementation of garlic.
grade-c - - See study
CD4+ Lymphocytes do not appear to be influence with supplementation of garlic
grade-c - - See study
CD8+ Lymphocytes do not appear to be influenced with supplementation of garlic.
grade-c - - See study
No significant influence of garlic supplementation has been found on cortisol in cancer patients.
grade-c - - See study
No significant influence of garlic supplement on creatinine concentrations in serum are present.
grade-c - - See study
No significant alterations in food intake are seen with garlic ingestion (assuming no taste aversion).
grade-c - Very High See 2 studies
800mg aged garlic extract has failed to reduce the risk of developing gastric cancer when taken daily for 7.3 years
grade-c - Very High See 2 studies
No significant alterations in homocysteine concentrations are seen with garlic supplementation.
grade-c - - See study
In persons with metabolic syndrome, there is no significant influence on fasting insulin concentrations relative to placebo after supplementation of garlic.
grade-c - - See study
There is no significant influence on insulin sensitivity when garlic is given to persons with metabolic syndrome.
grade-c - - See study
No significant influence on circulating IL-1 concentrations seen with garlic supplementation (alongside no influence on IL-6 yet a decrease in TNF-α)
grade-c - Very High See 2 studies
Supplementation of garlic to persons in chronic pro-inflammatory states does not seem to significantly influence circulating IL-6 concentrations
grade-c - - See study
In a study that noted an increase in adiponectin in persons with metabolic syndrome, there was no influence on circulating leptin concentrations.
grade-c - - See study
Quality of life in cancer patients is unaffected despite an increase in NK cell activity, thought to be indicative of a therapeutic effect of supplementation.
grade-c - - See study
There are no alterations in red blood cell count with normal doses of garlic (although there does appear to be a decrease when a toxic dose of garlic oil is ingested)
grade-c - - See study
Despite any possible interactions with the platelets (in regards to preventing their clotting), there are no alterations in the overall amount of platelets.
grade-c - Very High See 2 studies
Although there are theoretical benefits of garlic to weight loss, prolonged supplementation of garlic in other studies (where weight is measured as a secondary parameter of interest) is not altered. The weight loss effects are either small or nonexistent in otherwise normal conditions
grade-d Notable - See study
Topical application of a solution containing the sulfur bearing molecule Ajoene was able to half the tumor size and Bcl-2 expression after half a year of once daily application.
grade-d Notable - See study
The lone study noted that interferon alpha concentrations in serum increased 384% when measured 2-4 hours after 2g of raw garlic clove.
grade-d Notable - See study
Mineral bioaccumulation from garlic ingestion (allicin in particular) is reduced in persons working in a car battery factory with excessive lead levels to a level similar to the reference drug D-penicillamine
grade-d Notable - See study
The lone study assessing nitric oxide and garlic noted that a raw garlic clove (2g) could increase nitric oxide by 224% in otherwise healthy persons within 2-4 hours of ingestion; potency did not decrease after seven days
grade-d Notable - See study
The lone pilot study has noted a 32% reduction in prostatic size after a month of eating 200mg/kg garlic (as a water soluble liquid extract)
grade-d Notable - See study
The lone study (no placebo control) noted a 60% reduction in both total and free PSA in a small group of men with prostate cancer; requires more evidence to evaluate the therapeutic potential
grade-d Minor - See study
Urinary biomarkers of DNA damage are reduced in hypertensive persons following supplementation of garlic.
grade-d Minor - See study
In persons with coronary heart disease, supplementation of garlic appears to increase physical performance when ingested at a food dose (1g) daily over six weeks; the increase in performance is moderate.
grade-d Minor - See study
Oxidative biomarkers in the blood appear to be modestly reduced following supplementation of garlic in persons with high levels of oxidative damage indicative in serum.
grade-d Minor - See study
A decrease was noted alongside improvements in prostatic size, but a magnitude of reduction was not given for evaluation.
grade-d - - See study
The overall mortality rate from stomach cancer is not influence with garlic supplementation during 15 years of followup
grade-d - - See study
The protective effect of 800mg aged garlic extract daily for 7.3 years does not appear to be statistically significant
grade-d - - See study
Large doses of garlic (4.5g of the bulb) to athletes undergoing hypoxic training does not appear to increase performance.
grade-d - High See all 4 studies
There is no inherent influence of garlic on heart rate, although when garlic aids cardiovascular performance in persons with heart problems it is associated with a reduced heart rate relative to control (due to less stress on the tissue).
grade-d - Very High See 2 studies
Despite potent antibacterial properties of garlic oil when tested outside of the body, it appears to be ineffective when given to human volunteers.
grade-d - - See study
In otherwise healthy athletes given 4.5g of garlic cloves daily before a performance test, the lack of increased performance is met by a lack of changes in oxygen uptake.
grade-d - - See study
No significant interactions with Thromboxane A2 are currently known.
grade-d - - See study
No significant interactions with uric acid concentrations in serum.

Studies Excluded from Consideration

NOTE: The above table includes studies on Aged Garlic Extract as well as Garlic Oil supplementation, and may include studies on raw garlic consumption. They are not always interchangeable so read the context areas.

  • Confounded with other nutraceuticals[2][3]

  • Used alongside pharmaceuticals (adjuvant therapy)[4][5]

  • Confounded with CoQ10[6]

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Frequently Asked Questions and Articles on Garlic

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Things to Note

Primary Function:

Also Known As

Allium sativum, Vegetable Viagra, Da suan, Camphor of the poor, Lasun, Stinking Rose, Ail, Ajo

Do Not Confuse With

Tulbaghia violacea (Wild garlic or sweet garlic)

Goes Well With

  • Tazma Honey (for antibacterial purposes)

Caution Notice

Potential blood thinning properties at higher doses

Known to interact with some pharmaceuticals

  • The lowest estimated 'toxic' dose associated with raw garlic consumption has been noted to be a human equivalent of 400mg/kg (or 25g of raw garlic), which resulted in testicular toxicity

  • It is possible to be allergic to garlic supplements, if you are allergic to garlic itself

  • 8g (about two large cloves) of garlic can cut blood levels of Saquinavir in half

  • While moderate dietary intake of garlic does not reduce platelet aggregation or adversely interact with Warfarin, higher doses (2,400-7,200mg of Aged Garlic Extract) may do so

  • Contrary to popular belief, garlic may attract vampires[1]

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