Green Tea
  Uses of this Herb
Common Cold
Radiation Damage
  Herbs with Similar Uses
View List by Use
  Drugs that Interact
Beta-Lactam Antibiotics
  Herbs with Similar Side Effects
View List by Side Effect
  Herbs with Similar Warnings
View List by Warning
  Learn More About
Western Herbalism
Look Up > Herbs > Green Tea > Interactions
Interactions with Green Tea
Beta-Lactam Antibiotics

In an in vitro study, epicatechin gallate, a catechin constituent of green tea leaves, was shown to markedly lower the minimum inhibitory concentration of beta-lactam antibiotics against methicillin-resistant Staphylococcus aureus (MRSA) (Shiota et al. 1999). Epicathechin gallate may restore the effectiveness of beta-lactam antibiotics against MRSA, a major cause of nosocomial infections in hospitals that is resistant to many antibacterial agents including beta-lactams.


Theanine, a water-soluble amino acid from green tea leaves, has been shown to enhance the anti-tumor activity of doxorubicin in mice. In one study, the combination of theanine (10 mg/kg/day) with doxorubicin (2 mg/kg/day) reduced the tumor weight to 30% of the control level and inhibited hepatic metastasis of M5076 ovarian sarcoma (Sugiyama and Sadzuka 1999). In another study, administration of green tea powder (1 g/kg/day po for 4 days) to Ehrlich ascites carcinoma tumor-bearing mice enhanced the inhibitory effects of doxorubicin on tumor growth 2.5-fold (Sadzuka et al. 1998). Coadministration of doxorubicin with green tea increased the concentration of doxorubicin in the tumor, but not in normal tissue. Patients undergoing chemotherapy may benefit from drinking green tea, although clinical trials are needed to confirm these results.


In one study, a combination of green tea extract and tamoxifen significantly enhanced induction of apoptosis by (-)-epigallocatechin gallate (EGCG) in vitro (Suganuma et al. 1999). Drinking green tea may enhance the cancer-preventive activity of tamoxifen, requiring smaller doses with potentially fewer side effects.


Drinking large amounts of green tea may decrease the effectiveness of warfarin. Green tea contains vitamin K (approximately 0.03 microgram of vitamin K/100 g of brewed tea), which is known to inhibit the effects of warfarin (Taylor and Wilt 1999). In one case study, green tea consumption was reported to cause a fall in INR from a high of 3.79 to a low of 1.14 in a man treated with warfarin. He had begun drinking one-half to one gallon of green tea daily during his course of therapy with warfarin. The INR increased to 2.55 after discontinuation of the tea.


Sadzuka Y, Sugiyama T, Hirota S. Modulation of cancer chemotherapy by green tea. Clin Cancer Res. 1998;4:153-156.

Shiota S, Shimizu M, Mizushima T, Ito H, et al. Marked reduction in the minimum inhibitory concentration (MIC) of -lactams in methicillin-resistant Staphylococcus aureus produced by epicatechin gallate, an ingredient of green tea (Camellia sinensis). Biol. Pharm. Bull. 1999;22(12):1388-1390.

Suganuma M, Okabe S, Kai Y, Sueoka N, et al. Synergistic effects of (-)-epigallocatechin gallate with (-)-epicatechin, sulindac, or tamoxifen on cancer-preventive activity in the human lung cancer cell line PC-9. Cancer Res. 1999;59:44-47.

Sugiyama T, Sadzuka Y. Combination of theanine with doxorubicin inhibits hepatic metastasis of M5076 ovarian sarcoma. Clin Cancer Res. 1999;5:413-416.

Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann Pharmacother. 1999;33:426-428.Tyler V. Herbs of Choice: The Therapeutic Use of Phytomedicinals. Binghamton, NY: Pharmaceutical Products Press; 1994.

Copyright © 2000 Integrative Medicine Communications

This publication contains information relating to general principles of medical care that should not in any event be construed as specific instructions for individual patients. The publisher does not accept any responsibility for the accuracy of the information or the consequences arising from the application, use, or misuse of any of the information contained herein, including any injury and/or damage to any person or property as a matter of product liability, negligence, or otherwise. No warranty, expressed or implied, is made in regard to the contents of this material. No claims or endorsements are made for any drugs or compounds currently marketed or in investigative use. The reader is advised to check product information (including package inserts) for changes and new information regarding dosage, precautions, warnings, interactions, and contraindications before administering any drug, herb, or supplement discussed herein.