Garlic

On this page:

• What Garlic Is Used For
• How Garlic Is Used
• What the Science Says
• Side Effects and Cautions
• Sources
• For More Information

Introduction

This fact sheet provides basic information about garlic—uses, potential side effects, and resources for more information. Garlic is the edible bulb from a plant in the lily family. It has been used as both a medicine and a spice for thousands of years.

What Garlic Is Used For

• Garlic’s most common uses as a dietary supplementA product that contains vitamins, minerals, herbs or other botanicals, amino acids, enzymes, and/or other ingredients intended to supplement the diet. The U.S. Food and Drug Administration has special labeling requirements for dietary supplements and treats them as foods, not drugs. are for high cholesterol, heart disease, and high blood pressure.
• Garlic is also used to prevent certain types of cancer, including stomach and colon cancers.

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How Garlic Is Used

Garlic cloves can be eaten raw or cooked. They may also be dried or powdered and used in tablets and capsules. Raw garlic cloves can be used to make oils and liquid extracts.

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What the Science Says

• Some evidence indicates that taking garlic can slightly lower blood cholesterol levels; studies have shown positive effects for short-term (1 to 3 months) use. However, an NCCAM-funded study on the safety and effectiveness of three garlic preparations (fresh garlic, dried powdered garlic tablets, and aged garlic extract tablets) for lowering blood cholesterol levels found no effect.
• Preliminary research suggests that taking garlic may slow the development of atherosclerosis (hardening of the arteries), a condition that can lead to heart disease or stroke.
• Evidence suggests that taking garlic may slightly lower blood pressure, particularly in people with high blood pressure.
• Some studies suggest consuming garlic as a regular part of the diet may lower the risk of certain cancers. However, no clinical trials have examined this. A clinical trial on the long-term use of garlic supplements to prevent stomach cancer found no effect.
• Recent NCCAM-funded research includes studies on how garlic interacts with certain drugs; its effects on liver function and the dilation and constriction of blood vessels; and the bioavailability (how well a substance is absorbed by the body) of allicin, the main active compound of garlic.

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Side Effects and Cautions

• Garlic appears to be safe for most adults.
• Side effects include breath and body odor, heartburn, upset stomach, and allergic reactions. These side effects are more common with raw garlic.
• Garlic can thin the blood (reduce the ability of blood to clot) in a manner similar to aspirin. This effect may be a problem during or after surgery. Use garlic with caution if you are planning to have surgery or dental work, or if you have a bleeding disorder.
• Garlic has been found to interfere with the effectiveness of saquinavir, a drug used to treat HIV infection. Its effect on other drugs has not been well studied.
• Tell all your health care providers about any complementary and alternative practices you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care. For tips about talking with your health care providers about CAMA group of diverse medical and health care systems, practices, and products that are not presently considered to be part of conventional medicine. Complementary medicine is used together with conventional medicine, and alternative medicine is used in place of conventional medicine., see NCCAM’s Time to Talk campaign.

Search the scientific literature for potential herb-drug interactions

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Sources

• Agency for Healthcare Research and Quality. Garlic: Effects on Cardiovascular Risks and Disease, Protective Effects Against Cancer, and Clinical Adverse Effects. Evidence Report/Technology Assessment no. 20. Rockville, MD: Agency for Healthcare Research and Quality; 2000. AHRQ publication no. 01-E023.
• Gardner CD, Lawson LD, Block E, et al. Effect of raw garlic vs. commercial garlic supplements on plasma lipid concentrations in adults with moderate hypercholesterolemia: a randomized clinical trial. Archives of Internal Medicine. 2007;167(4):346–353.
• Garlic. In: Blumenthal M, Goldberg A, Brinckman J, eds. Herbal Medicine: Expanded Commission E Monographs. Newton, MA: Lippincott Williams & Wilkins; 2000:139–148.
• Garlic. Natural Medicines Comprehensive Database Web site. Accessed at www.naturaldatabase.com on June 16, 2009.
• Garlic (Allium sativum L.). Natural Standard Database Web site. Accessed at www.naturalstandard.com on June 16, 2009.
• Milner JA. Garlic (Allium sativum). In: Coates P, Blackman M, Cragg G, et al., eds. Encyclopedia of Dietary Supplements. New York: NY: Marcel Dekker; 2005:229–240.
• National Cancer Institute. Garlic and Cancer Prevention: Questions and Answers. National Cancer Institute Web site. Accessed at www.cancer.gov/cancertopics/factsheet/Prevention/garlic-and-cancer-prevention on June 3, 2010.

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