Garlic is an herb. It is best known as a flavoring for food. But over the years, garlic has been used as a medicine to prevent or treat a wide range of diseases and conditions. The fresh clove or supplements made from the clove are used for medicine.Garlic is used for many conditions related to the heart and blood system.These conditions include high blood pressure, high cholesterol, coronary heart disease, heart attack, and âhardening of the arteriesâ (atherosclerosis).arlic produces a chemical called allicin. This is what seems to make garlic work for certain conditions. Allicin also makes garlic smell. Some products are made âodorlessâ by aging the garlic, but this process can also make the garlic less effective.