Garlic

© Steven Foster

This fact sheet provides basic information about garlic—common 

names, what the science says, potential side effects and cautions, and 

resources for more information.

Common Name—garlic

Latin Name—Allium sativum

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. Garlic’s most 

common folk or traditional uses as a dietary supplement are for high 

cholesterol, heart disease, and high blood pressure. Other folk or 

traditional uses include prevention of certain types of cancer, including 

stomach and colon cancers. 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.

What the Science Says 

• Some evidence indicates that taking garlic can slightly lower blood 

cholesterol levels; studies have shown positive effects for shortterm (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.
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 health 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 complementary and alternative medicine, see 

NCCAM’s Time to Talk campaign at nccam.nih.gov/timetotalk/. 

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. National Cancer Institute Web site. Accessed at www.cancer.gov/cancertopics/

factsheet/Prevention/garlic-and-cancer-prevention on June 3, 2010.

For More Information

Visit the NCCAM Web site at nccam.nih.gov and view Using Dietary Supplements Wisely (nccam.nih.gov/health/supplements/wiseuse.htm).

NCCAM Clearinghouse

Toll-free in the U.S.: 1-888-644-6226

TTY (for deaf and hard-of-hearing callers): 1-866-464-3615

E-mail: info@nccam.nih.gov

PubMed®

Web site: www.ncbi.nlm.nih.gov/sites/entrez

NIH Office of Dietary Supplements

Web site: www.ods.od.nih.gov

NIH National Library of Medicine’s MedlinePlus

Garlic Listing: www.nlm.nih.gov/medlineplus/druginfo/natural/300.html

This publication is not copyrighted and is in the public domain. Duplication is encouraged.

NCCAM has provided this material for your information. It is not intended to substitute for the medical expertise and advice of your 

primary health care provider. We encourage you to discuss any decisions about treatment or care with your health care provider. The

mention of any product, service, or therapy is not an endorsement by NCCAM.

National Institutes of Health

♦♦♦

U.S. Department of Health and Human Services

D274

Created May 2006

Updated April 2012