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As a widely consumed beverage, green tea is generally regarded as safe. It does contain caffeine, at perhaps a slightly lower level than black tea, and can therefore cause insomnia, nervousness, and the other well-known symptoms of excess caffeine intake.
Green tea extracts, however, may not be safe. There are a growing number of case reports in which use of a concentrated green tea extract was associated with liver inflammation. 1 In most cases, liver problems disappeared after the extract was discontinued. But, in two cases, permanent liver failure ensued requiring liver transplantation. 2 While it is not absolutely certain that the green tea extract causedthe liver problems, nor how it might do so, these reports do raise significant concerns about use of green tea extracts, especially by those with liver disease or prone to it.
Green tea should not be given to infants and young children. There are theoretical concerns that high dosages of EGCG might be unsafe for pregnant women. 3 Dried green tea leaf contains significant levels of vitamin K on a per-weight basis. On this basis, it has been stated that people using blood thinners in the warfarin (Coumadin) family should avoid green tea, because vitamin K antagonizes the effect of those drugs. However green tea taken as a beverageprovides such small amounts of the vitamin that the risk seems minimal for normal consumption. There is one case report of problems that developed in a person on warfarin who consumed as much as a gallon of green tea daily. 4
Interactions You Should Know About
If you are taking:
- MAO inhibitors : The caffeine in green tea could cause serious problems.
- Warfarin (Coumadin) : Avoid drinking large quantities of green tea.
- Bonkovsky HL. Hepatotoxicity associated with supplements containing Chinese green tea (Camellia sinensis). Ann Intern Med. 2006;144:68-71. Erratum in: Ann Intern Med. 2006;144:380.
- Gloro R, Hourmand-Ollivier I, Mosquet B, Mosquet L, Rousselot P, Salamé E, Piquet MA, Dao T. Fulminant hepatitis during self-medication with hydroalcoholic extract of green tea. Eur J Gastroenterol Hepatol. 17(10):1135-7.
- Green tea mechanism urges caution for pregnant women. Nutra Ingredients website. http://nutraingredients.com/news/ng.asp?id=58807&n=dt76&c=tbtcgrwexqoosjy. Accessed September 20, 2005.
- Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann Pharmacother. 33(4):426-8.
- Alemdaroglu NC, Dietz U, Wolffram S, Spahn-Langguth H, Langguth P. Influence of green and black tea on folic acid pharmacokinetics in healthy volunteers: potential risk of diminished folic acid bioavailability. Biopharm Drug Dispos. 29(6):335-48.