Viral Upper Respiratory Infections (Colds and Influenza)
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Viral Upper Respiratory Infections (Colds and Influenza) and Green Tea

Green tea is a popular and potentially medicinal beverage. Extracts are made to concentrate the active properties of green tea. A gargle made from green tea extract has shown promise for preventing the flu, and the oral consumption of a green tea extract might help prevent both colds and flus.

Effect of Green Tea on Viral Upper Respiratory Infections (Colds and Influenza)

Green tea contains high levels of substances called catechin polyphenols, known to possess strong antioxidant, anticarcinogenic, antitumorigenic, and even antibiotic properties.1

Read more details about Green Tea.

Research Evidence on Green Tea

In a double-blind, placebo-controlled study,156 124 residents of a Japanese nursing home gargled with green tea catechins or placebo for three months. All participants received standard influenza vaccine. The results showed that residents who gargled with the tea extract were less likely to develop influenza than those using the placebo. In addition, another double-blind study found preliminary evidence that oral consumption of a green tea extract might help prevent both colds and flus.163

How to Use Green Tea

A typical dosage is 100 mg to 150 mg three times daily of a green tea extract standardized to contain 80% total polyphenols and 50% epigallocatechin gallate.

Safety Issues

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.
  • Folic acid : Green tea may decrease the absorption of folic acid into the blood stream. 5


  1. 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.
  2. 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.
  3. Green tea mechanism urges caution for pregnant women. Nutra Ingredients website. Accessed September 20, 2005.
  4. Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann Pharmacother. 33(4):426-8.
  5. 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.
  1. Snow JM. Camellia sinensi (L.) Kuntze (Theaceae). J Botanical Medicine. 1995;Autumn:28-32.
  2. Yamada H, Takuma N, Daimon T, et al. Gargling with tea catechin extracts for the prevention of influenza infection in elderly nursing home residents: a prospective clinical study. J Altern Complement Med. 2006;12:669-672.
  3. Rowe CA, Nantz MP, Bukowski JF, et al. Specific formulation of Camellia sinensis prevents cold and flu symptoms and enhances T cell function: a randomized, double-blind, placebo-controlled study. J Am Coll Nutr. 2007;26:445-452.

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