Green tea and its extracts may provide substantial benefit for body terrain factors, especially body weight, high blood sugar and insulin resistance, inflammation, oxidative stress, each of which is linked to cancer development and growth.
Safety and precautions
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
Green tea consumption affects the risk of breast cancer in postmenopausal women according to the age of onset of tea drinking: green tea is protective against cancer for women who started before age 20 but increases risk for those who started after age 50.4Yeung KS, Gubili J, Mao JJ. Herb-drug interactions in cancer care. Oncology (Williston Park). 2018 Oct 15;32(10):516-20.
- A higher risk for esophageal, pancreatic, and urinary tract cancers plus leukemia among people drinking higher levels of green tea in some studies in a systematic review5Filippini 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.
- A higher risk of prostate cancer among people treated with green tea supplements in a systematic review6Filippini 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.
- A weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward higher cancer mortality among people without cancer at baseline drinking the highest levels of green tea compared to the lowest levels in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 6 observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods studies7Tang 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.
- Weak trends toward higher risk of stomach cancer among people drinking green tea at the hottest temperatures compared to cool or warm tea in a meta-analysis of 3 observational studies8Huang 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.
Green tea combined with other therapies
High doses of lycopene, selenium, and green tea catechins together have been linked to higher incidence of prostate cancer among people with primary multifocal high grade prostatic intraepithelial neoplasia (mHGPIN) and/or atypical small acinar proliferation.
- Higher incidence of prostate cancer at re-biopsy among people with primary multifocal high grade prostatic intraepithelial neoplasia (mHGPIN) and/or atypical small acinar proliferation (ASAP) treated with 35 mg lycopene, 55 µg selenium, and 600 mg green tea catechins for 6 months compared to placeboa pill, medicine, or procedure—thought to be both harmless and ineffective—prescribed for the psychological benefit to the patient or as a sham treatment in a study to allow a comparison to a therapy of interest in a small RCTrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects9Gontero P, Marra G et al. A randomized double-blind placebo controlled phase I-II study on clinical and molecular effects of dietary supplements in men with precancerous prostatic lesions. Chemoprevention or “chemopromotion”? Prostate. 2015 Aug 1;75(11):1177-86.
Interactions with cancer treatments
Green tea capsules with 300 mg EGCG for 14 days did not show any effect on endoxifen, the most relevant active metabolite of tamoxifen, among people with breast cancer treated with tamoxifen for at least 3 months.10Braal 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.
In preclinical studiestesting a drug, a procedure, or another medical treatment in isolated cells or in animals; preclinical evidence is considered only an initial indication of possible effects in people EGCG reduces the effect of the chemotherapy drug bortezomib (Velcade), used primarily in multiple myeloma.11Modernelli A, Naponelli V et al. EGCG antagonizes bortezomib cytotoxicity in prostate cancer cells by an autophagic mechanism. Scientific Reports. 2015 Oct 16;5:15270; Yeung KS, Gubili J, Mao JJ. Herb-drug interactions in cancer care. Oncology (Williston Park). 2018 Oct 15;32(10):516-20; Golden EB, Lam PY et al. Green tea polyphenols block the anticancer effects of bortezomib and other boronic acid-based proteasome inhibitors. Blood. 2009 Jun 4;113(23):5927-37; Yang H, Zonder JA, Dou QP. Clinical development of novel proteasome inhibitors for cancer treatment. Expert Opinion on Investigational Drugs. 2009 Jul;18(7):957-71. Other interactions with cancer treatments:
- Green tea increased cell toxicity when used in combination with tamoxifen and irinotecan.12Yeung KS, Gubili J, Mao JJ. Herb-drug interactions in cancer care. Oncology (Williston Park). 2018 Oct 15;32(10):516-20.
- Large amounts of green tea can enhance levels of 5-fluorouracil.13Green Tea—Uses, Side Effects, and More. Interactions. Web MD. Viewed February 6, 2024.
- Green tea reduces the effects of imatinib (Gleevec).14Green Tea—Uses, Side Effects, and More. Web MD. Viewed February 6, 2024.
- EGCG amplifies the toxicity of cisplatin in ovarian and colorectal cancer cells.15Hu F, Wei F et al. EGCG synergizes the therapeutic effect of cisplatin and oxaliplatin through autophagic pathway in human colorectal cancer cells. Journal of Pharmacological Sciences. 2015 May;128(1):27-34; Chan MM, Soprano KJ, Weinstein K, Fong D. Epigallocatechin-3-gallate delivers hydrogen peroxide to induce death of ovarian cancer cells and enhances their cisplatin susceptibility. Journal of Cell Physiology. 2006 May;207(2):389-96.
Side effects or adverse events
Green tea extract has been found to have a low rate of adverse events,16Seufferlein 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. tolerable at doses up to 4.2 g per m2 once a day or 1.0 g per m2 3 times a day17Pisters 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. or at least 400 mg per day.18Crew KD, Brown P et al. Phase IB randomized, double-blinded, placebo-controlled, dose escalation study of Polyphenon E in women with hormone receptor-negative breast cancer. Cancer Prevention Research (Philadelphia). 2012 Sep;5(9):1144-54.
Drinking green tea or taking green tea extracts with food may reduce the risk of adverse events. A review of 216 case reports of adverse events concluded that “green tea concentrated extracts on an empty stomach is more likely to lead to adverse effects than consumption in the fed state.”19Sarma 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:20Filippini 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
Moderate to severe local skin reactions found with use of 10% sinecatechins ointment include redness (erythema), swelling (edema), erosions, crusts, and itching.21Kessels 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.
Less common adverse events:22Filippini 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 reactions
- Dizziness
- Heartburn
- Increased thirst
Interactions with other therapies
Green tea/EGCG also interacts with several pharmaceutical drugs and the absorption of iron. These and many more common drugs may interact with green tea or its constituents:23Green Tea—Uses, Side Effects, and More. Web MD. Viewed February 6, 2024.
- Acetaminophen
- Antibiotics (Quinolone antibiotics)
- Atorvastatin (Lipitor)
- Birth control pills
- Cimetidine (Tagamet)
- Ephedrine
- Estrogens
- Warfarin (Coumadin)
See Green Tea—Uses, Side Effects, and More › for a full list of interactions.
Do not use (contraindications)
Green tea use may not be compatible with some conditions and circumstances such as pregnancy or chemotherapy treatment. Web MD advises not to take green tea when taking ephedrine, nadolol (Corgard), or atorvastatin (Lipitor) due to serious interactions.24Green Tea—Uses, Side Effects, and More. Web MD. Viewed February 6, 2024.
Commentary
Advice from CancerChoices advisor Lise Alschuler, ND, FABNO, regarding safe use of green tea:
Green tea should never be taken on an empty stomach. Green tea should also be taken, or drunk, with food. This avoids potential mild liver toxicity.
Non-organic green tea can concentrate pesticide residues and should not be consumed regularly. Organic tea has fewer to no pesticide residues. See the case study below.
Side effects from green tea are rare, and, if they occur, may include nausea, diarrhea, and palpitations.
Green tea may interfere with bortezomib, blood thinners (warfarin and Coumadin), and anti-androgens but does not appear to negatively affect other chemotherapy agents.
The use of green tea extract nutritional products should be guided by a qualified health professional.
The importance of organic green tea: case study
CancerChoices advisor Lise Alschuler, ND, FABNO, shares this case from her experience: Sally is a 58-year-old woman diagnosed with early stage breast cancer who had recently undergone a lumpectomy. As recommended by her oncologist, Sally was taking an aromatase inhibitor predicted to halve her risk of breast cancer recurrence.
Sally read about the potential value of using green tea after surgery to reduce her risk of recurrence. She found a green tea product online and drank 4 cups every day. She did not inform her oncologist.
At Sally’s next follow-up visit, her oncologist informed her that her liver enzymes were elevated and that this could be an indication that the aromatase inhibitor may be causing liver toxicity. The oncologist stated that if the liver enzymes didn’t reduce, Sally may not be able to continue this medication.
Sally decided to consult a naturopathic oncologist, who then asked her about the green tea brand and determined that the green tea was not organic and may therefore have high levels of pesticide residues which can be toxic to the liver. The naturopathic oncologist advised Sally to stop the green tea and was able to send that product for testing (this is not commonly done due to the expense of product testing). The green tea that she had been drinking did, in fact, have high levels of pesticides.
When Sally stopped the green tea, her liver enzymes returned to normal range, and she was assured that she could safely continue the aromatase inhibitor. Once the liver enzymes were within normal range, the naturopathic oncologist recommended a high quality green tea product, and Sally’s liver enzymes remained within normal range.
Helpful links
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References