Garlic

Introduction

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

Common Names

• Garlic

Latin Names

• Allium sativum

What It Is Used For

• Garlic is commonly used as a dietary supplement containing vitamins, minerals, herbs, 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. Its primary uses include:
  • Managing high cholesterol, heart disease, and high blood pressure.
  • Preventing certain types of cancer, including stomach and colon cancers.

How It Is Used

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

What the Science Says

• Some evidence suggests that garlic can slightly lower blood cholesterol levels, particularly with short-term use (1 to 3 months). However, a study funded by NCCAM found no effect from garlic preparations on cholesterol levels.
• Preliminary research indicates that garlic may slow the development of atherosclerosis, a condition that can lead to heart disease or stroke.
• Evidence regarding garlic’s effect on blood pressure is mixed.
• Some studies suggest that regular consumption of garlic may lower the risk of certain cancers, although no clinical trials have confirmed this. A clinical trial on long-term garlic supplement use for stomach cancer prevention found no effect.
• Recent research includes studies on garlic’s interactions with certain drugs and its blood-thinning properties.

Side Effects and Cautions

• Garlic is generally safe for most adults.
• Common side effects include breath and body odor, heartburn, upset stomach, and allergic reactions, particularly with raw garlic.
• Garlic can thin the blood, similar to aspirin, which may pose risks during or after surgery. It is advisable to avoid garlic in your diet or as a supplement for at least one week before any surgical procedures.
• Garlic may interfere with the effectiveness of saquinavir, a drug used to treat HIV infection, though its effects on other medications are not well studied.
• It is essential to inform healthcare providers about complementary and alternative practices to ensure coordinated and safe care.

Sources

• 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.
• National Cancer Institute. Garlic and Cancer Prevention: Questions and Answers. National Cancer Institute Web site. Accessed at cancer.gov/newscenter/pressreleases/garlic on July 9, 2007.
• Agency for Healthcare Research and Quality. Garlic: Effects on Cardiovascular Risks and Disease, Protective Effects Against Cancer, and Clinical Adverse Effects. Accessed at ahrq.gov/clinic/epcsums/garlicsum.htm on July 9, 2007.
• Garlic. Natural Medicines Comprehensive Database Web site. Accessed July 3, 2007.
• Garlic (Allium sativum L.). Natural Standard Database Web site. Accessed June 28, 2007.
• Garlic. In: Blumenthal M, Goldberg A, Brinckman J, eds. Herbal Medicine: Expanded Commission E Monographs. Newton, MA: Lippincott Williams & Wilkins; 2000:139-148.
• 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.
• NCCAM National Institutes of Health