Garlic

Background

Garlic is the edible bulb from a plant in the lily family. It was traditionally used for health purposes by people in many parts of the world, including the Egyptians, Greeks, Romans, Chinese, Japanese, and Native Americans.

Currently, garlic is used as a dietary supplement for many purposes, including high blood cholesterol, high blood pressure, and the common cold, as well as in attempts to prevent cancer and other diseases.

Fresh garlic, garlic powder, and garlic oil are used to flavor foods. Garlic dietary supplements are sold as tablets or capsules. Garlic oil may be used topically (applied to the skin).

How Much Do We Know?

A great deal of research has been done on garlic, but much of it consists of small, preliminary, or low-quality studies.

What Have We Learned?

There’s conflicting evidence about whether garlic lowers blood cholesterol levels. If it does, the effect is small, and low-density lipoprotein (LDL) cholesterol (the so-called “bad” cholesterol that’s linked to increased heart disease risk) may not be reduced at all.

Garlic may be helpful for high blood pressure, but the evidence is weak.

Some studies indicate that certain groups of people who eat more garlic may be less likely to develop certain cancers, such as stomach and colon cancers. However, garlic in dietary supplement form has not been shown to help reduce the risk of these cancers. The National Cancer Institute recognizes garlic as one of several vegetables with potential anticancer properties but does not recommend using garlic dietary supplements for cancer prevention.

There’s not enough evidence to show whether garlic is helpful for the common cold.

What Do We Know About Safety?

Garlic is probably safe for most people in the amounts usually eaten in foods.

Side effects include breath and body odor, heartburn, and upset stomach. These side effects can be more noticeable with raw garlic. Some people have allergic reactions to garlic.

Taking garlic may increase the risk of bleeding. If you take an anticoagulant (blood thinner) such as warfarin (Coumadin) or if you need surgery, tell your health care provider if you’re taking or planning to take garlic dietary supplements.

Garlic has been found to interfere with the effectiveness of some drugs, including saquinavir, a drug used to treat HIV infection.

Keep in Mind

Tell all your health care providers about any complementary or integrative health approaches you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.

Key References