(See also Overview of Medicinal Herbs and Nutraceuticals.)
Garlic 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.
Garlic reduces the normal clotting tendency of particles in the blood that help stop bleeding (platelets). Because garlic stops microorganisms (such as bacteria) from reproducing, it can be used as an antiseptic and antibacterial. In large doses, garlic can slightly reduce blood pressure. Advocates suggest that garlic lowers levels of low-density lipoprotein (LDL)—the bad—cholesterol, and the overall evidence supports this beneficial effect. Claims that garlic helps prevent cancer are supported by little evidence. Garlic may slightly lower 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.
Garlic may interact with drugs that prevent blood clots (such as warfarin), increasing risk of bleeding. Thus, garlic should not be eaten or taken as a supplement one week before surgery or before a dental procedure. Garlic may interact with drugs used to treat HIV infections making them less effective, and may interact with drugs that decrease blood sugar levels causing excessive decreases in blood sugar levels.