Green Tea or EGCG for Cancer

Green Tea or EGCG for Cancer: Safety & Side Effects

This page covers safety information for Green Tea or EGCG. See our complete Green Tea or EGCG therapy guide →

Authors

Nancy Hepp, MS

past Lead Researcher

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Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS past Lead Researcher

Maria Williams

Research and Communications Consultant

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Maria Williams is a research and communications consultant who brings over 15 years’ experience in research, consumer education, and science communication to CancerChoices. She has worked primarily in public health and environmental health.

Maria Williams Research and Communications Consultant

Clinical reviewer

Andrew Jackson, ND

Research Associate

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Andrew Jackson, ND, serves as a CancerChoices research associate. As a naturopathic physician practicing in Kirkland, Washington, he teaches critical evaluation of the medical literture at Bastyr University in Kenmore, Washington. His great appreciation of scientific inquiry and the scientific process has led him to view research with a critical eye.

Andrew Jackson, ND Research Associate

Last update: June 30, 2026

Is green tea safe? 

Drinking green tea appears safe at regular, habitual and moderate use (three to nine cups per day).¹Kumar NB, Pow-Sang J et al. Randomized, placebo-controlled trial evaluating the safety of one-year administration of green tea catechins. Oncotarget. 2016 Oct 25;7(43):70794-70802; Joe AK, Schnoll-Sussman F et al. Phase Ib randomized, double-blinded, placebo-controlled, dose escalation study of Polyphenon E in patients with Barrett’s esophagus. Cancer Prevention Research (Philadelphia). 2015 Dec;8(12):1131-7; Dostal AM, Samavat H et al. The safety of green tea extract supplementation in postmenopausal women at risk for breast cancer: results of the Minnesota Green Tea Trial. Food and Chemical Toxicology. 2015 Sep;83:26-35. Side effects usually relate to gastrointestinal effects and nervous system effects from the caffeine in green tea. Green tea has more caffeine than black tea,²Zheng F, Chen K et al. Association between different types of tea consumption and risk of gynecologic cancer: a meta-analysis of cohort studies. Nutrients. 2023 Jan 13;15(2):403. so if caffeine is an issue for you, decaffeinated tea may be more suitable. A study found green tea extract supplements retain the beneficial effects of green tea without the side effects of caffeine.³Henning SM, Niu Y et al. Bioavailability and antioxidant activity of tea flavanols after consumption of green tea, black tea, or a green tea extract supplement. American Journal of Clinical Nutrition. 2004 Dec;80(6):1558-64.

Increased cancer risk

There isn’t strong evidence suggesting green tea consumption will increase risk of cancer. Weak evidence suggests a potential increase in risk for some cancer types associated with increased green tea consumption, but the data is not strong enough to be conclusive.⁴Filippini T, Malavolti M et al. Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database of Systematic Reviews. 2020 Mar 2;3(3):CD005004.; Tang J, Zheng JS et al. Tea consumption and mortality of all cancers, CVD and all causes: a meta-analysis of eighteen prospective cohort studies. British Journal of Nutrition. 2015 Sep 14;114(5):673-83.; Huang Y, Chen H et al. Association between green tea intake and risk of gastric cancer: a systematic review and dose-response meta-analysis of observational studies. Public Health Nutrition. 2017 Dec;20(17):3183-3192.

Interactions with cancer treatment

There have been a few studies to demonstrate potential interactions between EGCG and some chemotherapy treatments. It is important to discuss your supplement protocol with your doctor to ensure your cancer treatments are not compromised. 

• Bortezombi (Velcade), used primarily in multiple myeloma
• Potentially tamoxifen⁵Braal CL, Hussaarts KGAM et al. Influence of green tea consumption on endoxifen steady-state concentration in breast cancer patients treated with tamoxifen. Breast Cancer Research and Treatment. 2020 Nov;184(1):107-113.; Yeung KS, Gubili J, Mao JJ. Herb-drug interactions in cancer care. Oncology (Williston Park). 2018 Oct 15;32(10):516-20.
• Green tea reduces the effects of imatinib (Gleevec)⁶Green Tea—Uses, Side Effects, and More. Interactions. Web MD. Viewed February 6, 2024.
• Large amounts of green tea can enhance levels of 5-fluorouracil⁷Green Tea—Uses, Side Effects, and More. Interactions. Web MD. Viewed February 6, 2024.

Side effects and adverse reactions

Green tea extract has been found to have a low rate of adverse events.⁸Seufferlein T, Ettrich TJ et al. Green tea extract to prevent colorectal adenomas, results of a randomized, placebo-controlled clinical trial. American Journal of Gastroenterology. 2022 Jun 1;117(6):884-894; Lane JA, Er V et al. ProDiet: a phase ii randomized placebo-controlled trial of green tea catechins and lycopene in men at increased risk of prostate cancer. Cancer Prevention and Research (Philadelphia). 2018 Nov;11(11):687-696. Drinking green tea or taking green tea extracts with food may reduce the risk of adverse events.⁹Sarma DN, Barrett ML et al. Safety of green tea extracts: a systematic review by the US Pharmacopeia. Drug Safety. 2008;31(6):469-84. 

Common adverse events reported in studies:¹⁰Filippini T, Malavolti M et al. Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database of Systematic Reviews. 2020 Mar 2;3(3):CD005004; Tsao AS, Liu D et al. Phase II randomized, placebo-controlled trial of green tea extract in patients with high-risk oral premalignant lesions. Cancer Prevention Research (Philadelphia). 2009 Nov;2(11):931-41; Chow HH, Cai Y et al. Pharmacokinetics and safety of green tea polyphenols after multiple-dose administration of epigallocatechin gallate and Polyphenon E in healthy individuals. Clinical Cancer Research. 2003 Aug 15;9(9):3312-9; Laurie SA, Miller VA, Grant SC, Kris MG, Ng KK. Phase I study of green tea extract in patients with advanced lung cancer. Cancer Chemotherapy and Pharmacology. 2005 Jan;55(1):33-8; Pisters KM, Newman RA et al. Phase I trial of oral green tea extract in adult patients with solid tumors. Journal of Clinical Oncology. 2001 Mar 15;19(6):1830-8; Bedrood Z, Rameshrad M, Hosseinzadeh H. Toxicological effects of Camellia sinensis (green tea): a review. Phytotherapy Research. 2018 Jul;32(7):1163-1180; Choan E, Segal R et al. A prospective clinical trial of green tea for hormone refractory prostate cancer: an evaluation of the complementary/alternative therapy approach. Urolologic Oncology. 2005 Mar-Apr;23(2):108-13; Jatoi A, Ellison N et al. A phase II trial of green tea in the treatment of patients with androgen independent metastatic prostate carcinoma. Cancer. 2003 Mar 15;97(6):1442-6; Molinari M, Watt KD et al. Acute liver failure induced by green tea extracts: case report and review of the literature. Liver Transplantation. 2006 Dec;12(12):1892-5.

• Gastrointestinal disorders, primarily nausea but also vomiting, diarrhea, indigestion, or constipation; excess gas; upset stomach or stomach ache; or abdominal pain
• Headache
• Fatigue
• Muscle pain
• Elevation of liver enzymes or liver damage
• Nervousness
• Tremor
• Confusion

Less common adverse events:¹¹Filippini T, Malavolti M et al. Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database of Systematic Reviews. 2020 Mar 2;3(3):CD005004.

• Insomnia
• Raised blood pressure
• Skin/subcutaneous reactions, mainly rash or allergic skin reactions¹²Kessels J, Voeten L et al. Topical sinecatechins, 10%, ointment for superficial basal cell carcinoma: a randomized clinical trial. JAMA Dermatology. 2017 Oct 1;153(10):1061-1063.
• Dizziness 
• Heartburn
• Increased thirst

Contraindications

Green tea use may not be compatible with some conditions and circumstances such as pregnancy or chemotherapy treatment. Green tea may interfere with iron absorption. Caffeine may cause symptoms in people who are sensitive to caffeine or have certain health conditions.

Drug interactions 

These and many more common drugs may interact with green tea or its constituents:¹³Green Tea—Uses, Side Effects, and More. Interactions. Web MD. Viewed February 6, 2024. 

Interactions with medications and other interventions are complex. Always consult with a healthcare professional before adding any new therapy to your regimen. To learn more about interactions visit one of the trusted resources below: 

• About Herbs ›
• EfficaSafe ›

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