The sulfur compound allicin, produced by crushing or chewing fresh garlic or by taking powdered garlic products with allicin potential, in turn produces other sulfur compounds: ajoene, allyl sulfides, and vinyldithiins.¹ Aged garlic products lack allicin, but may have activity due to the presence of S-allylcysteine.

Many publications have shown that garlic supports the cardiovascular system. While earlier trials suggest it may mildly lower cholesterol and triglyceride levels in the blood,^{2, 3, 4} more recent trials found garlic to have minimal success in lowering cholesterol and triglycerides.^{5, 6, 7} Garlic also inhibits platelet stickiness (aggregation) and increases fibrinolysis,⁸ which results in a slowing of blood coagulation. It is mildly antihypertensive⁹ and has antioxidant activity.¹⁰

Garlic’s cardiovascular protective effects were illustrated in a four-year clinical trial on people 50–80 years old with atherosclerosis.¹¹ It was found that consumption of 900 mg of a standardized garlic supplement reduced arterial plaque formation by 5–18%. The benefits were most notable in women.

In test tube studies garlic has been found to have antibacterial, antiviral, and antifungal activity.¹² However, these actions are less clear in humans and do not suggest that garlic is a substitute for antibiotics or antifungal medications.

Human population studies suggest that eating garlic regularly reduces the risk of esophageal, stomach, and colon cancer.^{13, 14} This may be partly due to garlic’s ability to reduce the formation of carcinogenic compounds.