Green Tea 

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 Name—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. 

• Green tea and green tea extracts contain caffeine. Caffeine can cause 

insomnia, anxiety, irritability, upset stomach, nausea, diarrhea, or 

frequent urination in some people. Caffeine can also raise blood 
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pressure, and in very high doses, it can cause seizures, delirium, or irregular heart 

rhythms. 

• 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 herb or dietary supplement you are using, 

including green tea. This helps to ensure safe and coordinated care. 

Sources

National Cancer Institute. Tea and Cancer Prevention. National Cancer Institute Web site. Accessed at 

http://www.cancer.gov/newscenter/pressreleases/tea on May 1, 2006. 

Green tea. Natural Medicines Comprehensive Database Web site. Accessed at http://www.naturaldatabase.com on May 

1, 2006. 

Green tea (Camellia sinensis). Natural Standard Database Web site. Accessed at http://www.naturalstandard.com on 

May 1, 2006. 

For More Information

Visit the NCCAM Web site at nccam.nih.gov and view: 

• “What’s in the Bottle? An Introduction to Dietary Supplements” at nccam.nih.gov/health/bottle/ 

• “Herbal Supplements: Consider Safety, Too” at nccam.nih.gov/health/supplement-safety/ 

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 

CAM on PubMed

Web site: nccam.nih.gov/camonpubmed/ 

NIH Office of Dietary Supplements

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

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 

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U.S. Department of Health and Human Services