Green Tea
Keywords: Chinese tea, Japanese tea, cancer, mental alertness
© Steven Foster
On this page:
- Introduction
- What Green Tea Is Used For
- How Green Tea 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 Name—Camellia sinensis
What Green Tea 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 Green Tea 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 supports 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 all 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. For tips about talking with your health care providers about CAMA group of diverse medical and health care systems, practices, and products that are not presently considered to be part of conventional medicine. Complementary medicine is used together with conventional medicine, and alternative medicine is used in place of conventional medicine., see NCCAM's Time to Talk campaign.
Search the scientific literature for potential herb-drug interactions
Sources
- Green tea. Natural Medicines Comprehensive Database Web site. Accessed at www.naturaldatabase.com on July 8, 2009.
- Green tea (Camellia sinensis). Natural Standard Database Web site. Accessed at www.naturalstandard.com on July 8, 2009.
- National Cancer Institute. Tea and Cancer Prevention. National Cancer Institute Web site. Accessed at www.cancer.gov/newscenter/pressreleases/tea on June 3, 2010.
- 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.
For More Information
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
TTY (for deaf and hard-of-hearing callers): 1-866-464-3615
Web site: nccam.nih.gov
E-mail:
CAM on PubMed®
Web site: nccam.nih.gov/research/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 Publication No. D273
Created May 2006
Updated July 2010
* Note: PDF files require a viewer such as the free Adobe Reader.
