Does matcha powder (green tea) interact with warfarin?

Comment by InpharmD Researcher

While the information for matcha powder is lacking, a case report describes a patient who experienced inhibition of warfarin’s effect while drinking green tea. Both matcha powder and green tea are derived from the same plant and can potentially introduce vitamin K into the system. However, there is a lack of pharmacokinetic data on the interaction between green tea/matcha powder and warfarin which leaves the interaction open to speculation. The interaction was deemed moderate by a systematic review and is recommended to be managed with a consistent diet.

Background

Matcha powder and green tea are derived from the same plant source (Camellia sinensis). While there is a lack of data focusing on interactions between warfarin and matcha powder, two systematic reviews have discussed possible green tea interactions with cardiovascular agents. However, both studies have noted the scarcity of evidence. Due to the lack of pharmacokinetic interaction data, the main hypothesis is that green tea supplies vitamin K which may antagonize and decrease warfarin's anticoagulant effect. A 2020 systematic review cites the interaction as moderate and recommends consuming a consistent amount of green tea to lower the chance of fluctuating international normalized ratio (INR). [1], [2], [3]

References:

[1] Tan CSS, Lee SWH. Warfarin and food, herbal or dietary supplement interactions: A systematic review. Br J Clin Pharmacol. 2021;87(2):352-374. doi:10.1111/bcp.14404
[2] Werba JP, Misaka S, Giroli MG, et al. Update of green tea interactions with cardiovascular drugs and putative mechanisms. J Food Drug Anal. 2018;26(2S):S72-S77. doi:10.1016/j.jfda.2018.01.008
[3] Kochman J, Jakubczyk K, Antoniewicz J, Mruk H, Janda K. Health Benefits and Chemical Composition of Matcha Green Tea: A Review. Molecules. 2020;26(1):85. Published 2020 Dec 27. doi:10.3390/molecules26010085
Literature Review

A search of the published medical literature revealed 1 study investigating the researchable question:

Does matcha powder (green tea) interact with warfarin?

Please see Table 1 for your response.

 

Probable Antagonism of Warfarin by Green Tea

Design

 Case report

Case presentation

A 44-year-old caucasian male receiving warfarin therapy for 14 months with an international normalized ratio (INR) goal of 2.5 to 3.5 presented with a history of fluctuating INR values. Initial INR values were 3.20 one month prior to attending the clinic and 3.79 on the first day of clinic visit. No symptoms of excessive anticoagulation were reported. After being instructed to take 7.5 mg once daily, another visit 22 days later revealed an INR of 1.37. The patient did not follow up until one month later with a measured INR of 1.14. Investigations revealed the patient began to drink 1/2 to 1 gallon of green tea daily about a week prior to the 1.37 INR value.

The patient discontinued taking green tea and remained on the 7.5 mg warfarin dose. One week later, the INR was 2.55 and subsequent readings were either within range or slightly out of range.

Study Author Conclusions

 Warfarin is a highly effective oral anticoagulant, but it requires close monitoring to prevent complications. Patients receiving warfarin need to be routinely questioned about their intake of vitamin K–containing foods and beverages.
References:

Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann Pharmacother. 1999;33(4):426-428. doi:10.1345/aph.18238