Green Tea

Latin NameCamellia sinensis

Green Tea

Botanical Illustration of Camellia sinensis from Köhler's Medizinal-Pflanzen, 1887


Fresh leaves from the Camellia sinensis plant are steamed to produce green tea. Black tea and oolong tea are produced from the Camellia sinensis plant using different methods. Green tea is usually brewed and consumed as a beverage. Green tea extracts can be taken in capsules and are sometimes used in skin products.


A traditional beverage in China, Korea and Japan, green tea was believed to promote well being.   


Today, green tea and green tea extracts, such as its component EGCG, are used as an herbal remedy in the hope of improving mental alertness, aiding in weight loss, lowering cholesterol levels, and protecting skin from sun damage.


Laboratory studies suggest that green tea may help protect against certain cancers, but studies in people have shown mixed results.


Some research suggests that the use of green tea preparations can improve 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.


Side Effects and Cautions Summary


  • 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. 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.


  • 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 to help ensure coordinated and safe care. Complementary or alternative therapy should not be used in place of conventional medical care or to delay seeking that care.





For More Information


Using Dietary Supplements Wisely


The National Center for Complementary and Alternative Medicine (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: Contact NCCAM


NIH Office of Dietary Supplements

Web site:

NIH National Library of Medicine’s MedlinePlus

Green Tea Listing:

Source: National Center for Complementary and Alternative Medicine, Green Tea fact sheet, Created May 2006, Updated November 2008


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