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When green tea is consumed in the form of whole leaves, or if it is steeped long enough to contain tannins, vitamin K is generally present in amounts significant enough to counteract the effects of warfarin (117,118), but if green tea is steeped for a short time, and the leaves are not consumed, green tea has very low concentrations of vitamin K (182).

Caution use of whole green tea leaves or powder in patients taking warfarin which may make achievement of therapeutic PTINR difficult. Vitamin K levels in coffee and tea was performed which revealed that vitamin K concentrations were about 0.03 μg/100 mL or less, and according to this source, brewed tea or coffee contains extremely small amounts of vitamin K and is not a dietary source (119).