© Steven Foster
On this page:

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

Introduction
This fact sheet provides basic information about green tea—common names, uses, potential side effects, and resources for more information. All types of tea (green, black, and oolong) are produced from the Camellia sinensis plant using different methods. Fresh leaves from the Camellia sinensis plant are steamed to produce green tea.

Common Names—green tea, Chinese tea, Japanese tea
Latin Names—Camellia sinensis
What It Is Used For

• Green tea and green tea extracts, such as its component EGCG, have been used to prevent and treat a variety of cancers, including breast, stomach, and skin cancers.
• Green tea and green tea extracts have also been used for improving mental alertness, aiding in weight loss, lowering cholesterol levels, and protecting skin from sun damage.

How It Is Used
Green tea is usually brewed and drunk as a beverage. Green tea extracts can be taken in capsules and are sometimes used in skin products.
What the Science Says

• Laboratory studies suggest that green tea may help protect against or slow the growth of certain cancers, but studies in people have shown mixed results.
• Some evidence suggests that the use of green tea preparations improves mental alertness, most likely because of its caffeine content. There are not enough reliable data to determine whether green tea can aid in weight loss, lower blood cholesterol levels, or protect the skin from sun damage.
• NCCAM is supporting studies to learn more about the components in green tea and their effects on conditions such as cancer, diabetes, and heart disease.

Side Effects and Cautions

• Green tea is safe for most adults when used in moderate amounts.
• There have been some case reports of liver problems in people taking concentrated green tea extracts. This problem does not seem to be connected with green tea infusions or beverages. Although these cases are very rare and the evidence is not definitive, experts suggest that concentrated green tea extracts be taken with food, and that people should discontinue use and consult a heath care practitioner if they have a liver disorder or develop symptoms of liver trouble, such as abdominal pain, dark urine, or jaundice.
• Green tea and green tea extracts contain caffeine. Caffeine can cause insomnia, anxiety, irritability, upset stomach, nausea, diarrhea, or frequent urination in some people.
• Green tea contains small amounts of vitamin K, which can make anticoagulant drugs, such as warfarin, less effective.
• Tell 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.

Sources

• Sarma DN, Barrett ML, Chavez ML, et al. Safety of green tea extracts: a systematic review by the US Pharmacopeia. Drug Safety. 2008;31(6):469–484.
• National Cancer Institute. Tea and Cancer Prevention. National Cancer Institute Web site. Accessed on May 1, 2006.
• Green tea. Natural Medicines Comprehensive Database Web site. Accessed on May 1, 2006.
• Green tea (Camellia sinensis). Natural Standard Database Web site. Accessed on May 1, 2006.

NCCAM Clearinghouse
The NCCAM Clearinghouse provides information on CAM and NCCAM, including publications and searches of Federal databases of scientific and medical literature. The Clearinghouse does not provide medical advice, treatment recommendations, or referrals to practitioners.
Toll-free in the U.S.: 1-888-644-6226
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Web site: nccam.nih.gov
E-mail: info@nccam.nih.gov Contact NCCAM
CAM on PubMed
Web site: nccam.nih.gov/camonpubmed/
NIH Office of Dietary Supplements
Web site: ods.od.nih.gov
NIH National Library of Medicine's MedlinePlus
Green Tea Listing: www.nlm.nih.gov/medlineplus/druginfo/natural/patient-green_tea.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.
NCCAM Publication No. D273
Created May 2006
Updated November 2008
Information Provided By:
NCCAM
National Institutes of Health
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Bethesda, Maryland 20892 USA
E-mail: info@nccam.nih.gov