Garlic is an herb that has long been used in cooking and in medicine. When a garlic bulb is cut or crushed, an amino acid by-product called allicin is released. Allicin is responsible for garlic’s strong odor and medicinal properties.
Because the active ingredients are destroyed when the garlic is crushed, the amount of active ingredient in the various forms of garlic varies greatly. Aged garlic extract (AGE), made from garlic allowed to age for at least 20 months, has more stable active compounds than most forms. Consuming garlic supplements in this form appears to provide the greatest health benefits and with fewer adverse effects.
(See also Overview of Dietary Supplements.)
Claims for Garlic
Garlic reduces the normal clotting tendency of platelets (particles in the blood that help stop bleeding). Because garlic stops microorganisms (such as bacteria) from reproducing, it has some antiseptic and antibacterial effects. Proponents also claim that garlic can
Reduce low-density lipoprotein (LDL) cholesterol levels
Reduce the risk of cancers, particularly gastrointestinal cancers
Lower blood sugar levels
Garlic is also said to help prevent the common cold and to treat nonalcoholic fatty liver disease (NAFLD).
Evidence for Garlic
The strongest evidence available for garlic supplementation, specifically AGE, is for lowering blood pressure. In large doses, garlic can reduce systolic and diastolic blood pressure slightly.
The effect of garlic on lowering cholesterol has been inconsistent, but studies have shown it lowers levels of total cholesterol and low-density lipoprotein (LDL)—the bad—cholesterol, probably enough to meaningfully decrease risks of heart problems such as heart attacks.
Scientific evidence for either garlic intake and garlic supplement use shows limited or no protection against cancer.
A meta-analysis of 7 studies shows that garlic may lower fasting blood sugar levels.
Most studies have used aged garlic extracts. Preparations formulated to have little or no odor may be inactive and need to be studied.
Side Effects of Garlic
Garlic usually has no harmful effects other than making the breath, body, and breast milk smell like garlic. However, consuming large amounts can cause nausea and burning in the mouth, esophagus, and stomach.
Drug Interactions with Garlic
Small amounts of garlicgarlic should not be eaten or taken as a supplement 2 weeks before surgery or before a dental procedure.
Garlicmedications that decrease blood sugar levels causing excessive decreases in blood sugar levels.
Garlic can also add to the effects of blood pressure–lowering medications and thus lower blood pressure too much. Garlicgarlic
Recommendations for Garlic
Garlic appears to lower blood pressure, total cholesterol and LDL cholesterol levels, and fasting blood sugar levels. As a result, garlic may help decrease risks of cardiovascular problems. Garlic is relatively safe, but people should talk with their doctor before taking garlic if they
Have diabetes or HIV
Take anticoagulants
Take antihypertensives (for high blood pressure)
Take medications to prevent organ transplant rejection
Take medications to treat diseases such as tuberculosis
More Information
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
National Institutes of Health's National Center for Complementary and Integrative Health: Garlic
