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What is it? Overview Usage Side Effects and Warnings

Tea Side Effects and Warnings

Written by ColleenO.

Safety Issues--Green Tea

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.35,40,50 In most cases, liver problems disappeared after the extract was discontinued. But, in two cases, permanent liver failure ensued, requiring liver transplantation.36,40 While it is not absolutely certain that the green tea extract caused the 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.37

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 beverage provides 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.38

Interactions You Should Know About--Green Tea

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.51

Safety Issues--Black Tea

As an extraordinarily widely consumed beverage, black tea is presumed to have a high safety factor. Its side effects would be expected to be similar to those of coffee—heartburn, gastritis, insomnia, anxiety, and heart arrhythmias (benign palpitations or more serious disturbances of heart rhythm). All drug interactions that can occur with caffeine would be expected to occur with black tea.

Interactions You Should Know About--Black Tea

If you are taking:

  • MAO inhibitors: The caffeine in black tea could cause dangerous drug interactions.
  • Stimulant drugs such as Ritalin: The stimulant effects of black tea might be amplified.
  • Drugs to prevent heart arrhythmias or to treat insomnia, heartburn, ulcers, or anxiety: - Black tea might interfere with their action.
  • Folic acid: Black tea may decrease the absorption of folic acid into the blood stream.


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