Green Tea | Memorial Sloan Kettering Cancer Center

Green Tea
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Common Names
For Patients & Caregivers
Tell your healthcare providers about any dietary supplements you’re taking, such as herbs, vitamins, minerals, and natural or home remedies. This will help them manage your care and keep you safe.
What is it?
Green tea is a drink made from the Camellia sinensis plant. Fresh leaves are cut from this plant and steamed to make the tea.
You can drink green tea or take it orally (by mouth) in a pill or tablet as a dietary supplement. You can also use green tea extract on your skin as a cream.
What are the potential uses and benefits?
Green tea is used to:
Prevent heart disease
Prevent cancer
Green tea also has other uses that haven’t been studied by doctors to see if they work.
It’s generally safe to drink green tea and use it in food. Talk with your healthcare providers before taking green tea supplements. Herbal supplements are stronger than the herbs you would use in cooking.
Supplements can also interact with some medications and affect how they work. For more information, read the “What else do I need to know?” section below.
What are the side effects?
Side effects of taking green tea supplements may include:
Nausea (feeling like you’re going to throw up)
Stomach pain
Drinking too much green tea can disrupt your sleep, and can also give you headaches
What else do I need to know?
Talk to your doctor if you’re taking iron supplements. Green tea can affect the way iron is absorbed in the body.
Don’t drink green tea if you’re pregnant or breastfeeding. Green tea has caffeine in it that may cause your baby to have trouble sleeping.
Avoid drinking green tea if you have a stomach ulcer (sore in the lining of your stomach). Green tea may make your ulcer worse.
For Healthcare Professionals
Green tea is a beverage derived from the unfermented leaves of a plant native to Asia. Green tea extract is marketed as an antioxidant and dietary supplement to support cardiovascular, metabolic, cognitive, and cellular health. Active constituents include the polyphenol epigallocatechin-3-gallate (EGCG), caffeine, and theanine.
Green tea consumption may reduce risk for dementia (1), hypertension (2), cardiovascular disease (63), and all-cause but not cancer-related mortality (3)(4). Data are mixed on whether it can reduce risk of gastric and esophageal cancers (5)(6)(7). Other findings suggest preventive benefits with green tea and its active compounds against oral premalignant lesions (8) and for those at high risk of developing liver or colorectal cancers (9)(10) but not colorectal adenomas (64). There is no association between green tea and risk for malignant lymphoma or multiple myeloma (11), but intake may reduce risk for myelodysplastic syndrome (12) and kidney cancer (65).
In prostate cancer patients, a blend of green tea, pomegranate, broccoli, and curcumin had a protective effect following post-radical treatment (13). Green tea consumption also decreased PSA levels in patients prior to prostatectomy (14). However, combination supplementation with the highest nontoxic doses of green tea catechins, selenium, and lycopene was associated with an elevated incidence of prostate cancer in high-risk patients (15), and long-term intake of an EGCG product did not reduce prostate cancer risk (16).
Other limited data suggestoral EGCG may induce a biologic response in patients with chronic lymphocytic leukemia (17) or reduce radiation-induced esophagitis in lung cancer patients (18), but did not prevent recurrence in advanced ovarian cancer (19). Topical EGCG may help relieve radiation-induced dermatitis in breast cancer patients (20)(21), but these results are also preliminary.
Additional studies suggest positive effects of green tea on blood pressure and glycemic control in type-2 diabetes patients (66), and on weight reduction in women with polycystic ovary syndrome (67).
Moderate green tea consumption was not associated with increased risk of kidney stone formation (24), but the caffeinated form may cause insomnia and nausea. Animal models suggest use of green tea extract during fasting may increase toxicity risk (25). Clinical data show that EGCG 200 mg twice daily for one year is safe (26), whereas 800 mg daily was associated with elevated liver enzymes (27).
Purported Uses and Benefits
Cardiovascular support
Cancer prevention
Mechanism of Action
Green tea may confer cardiovascular protection by increasing HDL and lowering LDL and triglyceride levels (28). Blood pressure modulation may be mediated by EGCG which induces NO production that results in vasodilation (29). Neurocognitive benefits with green tea extract may occur from enhanced brain connectivity during working memory processing (30), and EGCG may inhibit tau protein aggregation to reduce toxicity in neuronal model cells (31).
Chemopreventive properties are attributed to polyphenols, particularly EGCG which may inhibit enzymes involved in cell replication and DNA synthesis (32). In vitro data suggest concentrations of 30 mcg/mL of EGCG and EGC inhibit arachidonic acid metabolism by 30–75%, which may reduce colon cancer risk (33). Other studies in human colon cancer cell lines suggest EGCG inhibits topoisomerase I but not II (34). It also inhibited DNA replication in leukemia cancer cell lines (35), and modulated VEGF leading to apoptosis in leukemic cells (36). An early animal study identified caffeine in green tea as an important component for inhibition of UVB light-induced carcinogenesis (37).
Warnings
The United States Pharmacopeia included this cautionary labeling requirement in its Powdered Decaffeinated Green Tea Extract monograph (38):
“Do not take on an empty stomach. Take with food. Do not use if you have a liver problem and discontinue use and consult a healthcare practitioner if you develop symptoms of liver trouble, such as abdominal pain, dark urine, or jaundice (yellowing of the skin or eyes).”
Adverse Reactions
Green tea is generally considered safe, but excessive consumption can disrupt sleep and cause headaches because of its caffeine content.
EGCG 200 mg twice daily with food for 1 year appeared to be safe in men at higher risk for prostate cancer (26).