Merck Manual

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Green Tea

By

Laura Shane-McWhorter

, PharmD, University of Utah College of Pharmacy

Medically Reviewed Jan 2022 | Modified Sep 2022
VIEW PROFESSIONAL VERSION

What is green tea?

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. Green tea contains caffeine, but many extracts have been decaffeinated. It is high in flavonoids, polyphenols, and catechins. Those substances are antioxidants Antioxidants The human body needs various vitamins and minerals in order to thrive. Many of these nutrients can be found in whole, non-processed foods such as fruits and vegetables. However, most modern... read more , often thought to protect cells from damage by oxygen, mutations, and cancer.

What claims are made about green tea?

Does green tea work?

Few of the benefits claimed for green tea are supported by strong scientific evidence. However, topical (applied directly on the wart) green tea may help treat genital warts. Studies have also shown a small but significant loss of weight among users.

What are the possible side effects of green tea?

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

What drug interactions occur with green tea?

Vitamin K in green tea may decrease anticoagulant effects of warfarin, thus increasing the risk of blood clots. Green tea may cause increased side effects (due to its caffeine) if combined with amphetamines or supplements that are stimulants, particularly ephedra and bitter orange. When combined with MAO inhibitors, blood pressure and heart rate may increase. Green tea may greatly decrease blood levels of nadolol, a beta blocker, as well as atorvastatin. Green tea may also decrease absorption of iron and folic acid.

Recommendations

Green tea is generally considered safe, although the health benefits, if any, are likely small. People should avoid drinking large amounts, especially if pregnant.

Drugs Mentioned In This Article

Generic Name Select Brand Names
No brand name available
Cafcit, NoDoz, Stay Awake, Vivarin
Folacin , Folicet, Q-TABS
NOTE: This is the Consumer Version. DOCTORS: VIEW PROFESSIONAL VERSION
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