Common Name: garlic

Scientific Name: Allium sativum

Background

• Garlic has been grown and used around the world for centuries. Historical records from civilizations like Egypt, India, and Greece document its application in cooking and in treating ailments such as digestive issues, respiratory infections, and headaches.

• Today, garlic is often taken as a supplement for various health reasons including managing high cholesterol, regulating blood pressure and blood sugar levels, supporting the immune system, and potentially lowering the risk of certain cancer types. It is also sometimes applied to the skin.

How Much Do We Know?

• There is a significant body of scientific work examining garlic, particularly its impact on cholesterol levels and blood fats.

What Have We Learned?

• Supplementing with garlic may slightly lower total cholesterol and LDL (“bad”) cholesterol in individuals with high cholesterol.

• A small reduction in blood pressure may occur in those with high readings when taking garlic supplements.

• There is minor evidence suggesting garlic may modestly reduce blood sugar in people dealing with diabetes.

• Research does not support garlic as effective in lowering the chances of stomach cancer, and its influence on colorectal cancer remains unclear.

• Garlic is sometimes marketed as an immune booster, but evidence is limited. A review from 2022 noted just two small studies suggesting a possible benefit, with limitations in their design.

What Do We Know About Safety?

• Garlic has been taken by mouth safely in studies lasting up to 7 years. Some forms used on the skin are also considered safe. However, fresh raw garlic applied directly to the skin can cause serious irritation or burns.

• Consuming garlic can lead to bad breath, body odor, stomach discomfort, gas, and nausea. In some cases, allergic reactions may occur.

• Garlic supplements could raise the risk of bleeding. It’s important to inform healthcare providers if you use them, especially before surgery or if you take blood-thinning medications such as anticoagulants or aspirin.

• Always consult a medical professional before using garlic supplements if you're on other medication, as harmful interactions are possible.

• During pregnancy or breastfeeding, garlic in amounts larger than typically found in food may not be safe when taken orally. Little is known about its safety when applied to the skin during these times.

Keep in Mind

• It’s important to keep your doctor informed about any alternative health practices you are exploring. Doing so ensures better decision-making together.

• Herbal products, depending on their use and form (oral or topical), are regulated in different ways. Many are sold as dietary supplements and follow different rules from prescription medicines.

• Dietary supplements are not approved by the U.S. Food and Drug Administration (FDA) before they reach consumers. If safety concerns arise after they're on the market, the FDA can take actions to protect public health. Manufacturers are tasked with ensuring their products are safe and properly labeled before sale.

For More Information

• Using Dietary Supplements Wisely

• Understanding Interactions Between Medications and Supplements

• How to Read and Understand Scientific Research Articles

NCCIH Clearinghouse

The NCCIH Clearinghouse shares information on alternative and integrative health topics and provides educational materials as well as help locating relevant scientific research. It does not provide medical guidance.

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

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PubMed®

Managed by the National Library of Medicine, PubMed® offers access to summaries and publication details from a wide range of scientific research in health and medicine.

Office of Dietary Supplements (ODS), National Institutes of Health (NIH)

The ODS works to expand understanding of dietary supplements, supports related research, and provides public education through fact sheets and other resources on various supplements like vitamin D or multivitamins.

Key References

• Abebe W. Overview of herbal remedies that might cause bleeding and considerations for dental treatment. EPMA Journal. 2019;10(1):51-64.

• Alam A et al. Traditional and pharmacological properties of Allium vegetables in treating inflammation and cancer. Critical Reviews in Food Science and Nutrition. 2023;63(23):6580-6614.

• Crawford C et al. Dietary supplement compounds aimed at supporting a healthy immune system: a systematic review. Nutrients. 2022;14(21):4604.

• Garlic profile. Natural Medicines database. Accessed December 5, 2023.

• Hatfield J et al. The link between dietary supplements and bleeding risks. Proceedings (Baylor University Medical Center). 2022;35(6):802-807.

• Hitl M et al. Review of skin burn cases caused by direct garlic application. American Journal of Emergency Medicine. 2021;44:5-10.

• Ried K et al. Updated analysis of garlic’s effects on blood cholesterol levels. Nutrition Reviews. 2013;71(5):282-299.

• Shabani E et al. Effect of garlic on cholesterol and glucose among diabetics: review and analysis. Primary Care Diabetes. 2019;13(1):28-42.

• Sun Y-E et al. Garlic’s ability to lower cholesterol and LDL: a meta-analysis. Medicine (Baltimore). 2018;97(18):e0255.

• Zhou X et al. Meta-analysis on garlic consumption and risk of colorectal cancer. Medicine (Baltimore). 2020;99(1):e18575.

This document is in the public domain and can be freely reproduced.

Information provided herein is meant for educational purposes and should not replace professional medical guidance. Always consult your healthcare provider for advice on treatments. Mention of any specific product or therapy does not imply endorsement.