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Green Tea


Laura Shane-McWhorter

, PharmD, University of Utah College of Pharmacy

Last full review/revision Jul 2020| Content last modified Jul 2020

Green tea is made from the dried leaves of the same plant as traditional tea. However, traditional tea leaves are fermented, and green tea leaves are steamed but unfermented. Green tea may be brewed and drunk or ingested in tablet or capsule form. It is thought to have effects that protect cells from damage by oxygen, mutations, and cancer. Green tea contains caffeine, but many extracts have been decaffeinated. It is high in flavonoids, polyphenols, and catechins.

(See also Overview of Dietary Supplements.)

Medicinal claims

Green tea is said to have multiple health benefits, few of which are supported by strong scientific evidence. People take green tea for many reasons, including prevention of cancer and coronary artery disease, as well as treatment of external genital warts. Other reasons are reduction of fat (lipid) levels in the blood, relief of osteoarthritis pain and menopausal symptoms, and enhancement of weight loss, memory, and longevity.

Possible side effects

Side effects are related to the effects of caffeine. They include insomnia, anxiety, rapid heart rate (tachycardia), and mild tremor. Pregnant women should avoid excessive caffeine. Rare case reports document liver toxicity.

Drug interactions

Vitamin K in green tea may decrease anticoagulant effects of warfarin, thus increasing the risk of blood clots.

More Information about Green Tea

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

  • National Institutes of Health (NIH), National Center for Complementary and Integrative Health: General information on the use of green tea as a dietary supplement

Drugs Mentioned In This Article

Generic Name Select Brand Names
warfarin COUMADIN

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