Green Tea Leaves


  • Vitamins & Supplements
  • Updated December 21, 2016

Green tea, white tea, and black tea are made from dried leaves of Camellia sinensis, a perennial evergreen shrub. Up to 40% of the dry weight of tea leaves is accounted for by antioxidants called catechins; epigallocatechin gallate (EGCG) is the most abundant catechin found in green tea. EGCG could theoretically promote brain health, but no studies have evaluated whether it can protect from cognitive decline or dementia. EGCG supplements are considered safe for most people but high doses may affect liver function.


Long-term studies are lacking and no studies have evaluated whether EGCG may slow cognitive decline or prevent dementia. Our search identified:

• 3 double-blind randomized clinical trials (1 in Down syndrome patients, 2 in healthy adults)
• 1 pilot clinical study in people with Down syndrome
• Numerous preclinical studies

Potential Benefit

Two small trials suggest that EGCG treatment may very modestly improve memory functions, inhibitory control, and adaptive behavior in people with Down syndrome, though this protective effect was evident in only 3 out of 24 cognitive tests [1][2]. In healthy adults, a single dose of EGCG has had little influence on cognition. One double-blind randomized controlled trial reported that a single treatment did not affect cognitive performance or mood [3]. A second trial reported increased calmness and reduced stress [4]. EGCG also increased brain waves, which have been associated with relaxation, focused attention, and quiet wakefulness [5]. Long-term studies in healthy people are needed to evaluate the effects of EGCG on cognitive health.

Preclinical studies have found a wide range of actions of EGCG, including chelating metals, reducing inflammation, scavenging free radicals, improving mitochondrial function, and preventing death of brain cells [6]. EGCG may also inhibit enzymes that break down the neurotransmitter acetylcholine [7][8], which is important for memory retrieval. Other preclinical studies found that EGCG treatment improved function or reduced damage in the brain [9-11], but these effects have not been confirmed in human trials.

For Dementia Patients

No studies have reported whether EGCG alone is beneficial to patients with dementia. While some benefits have been observed in preclinical studies of Alzheimer's disease, including improved cognitive function [9][10] and reduction of pathological markers of Alzheimer's [10], these effects have yet to be confirmed in people with dementia.


EGCG supplements are considered safe for most people when taken at commonly used doses (300–400 mg/day) [12][13], but high doses (800–1600 mg of EGCG per day) may negatively affect liver function [14]. Most safety data on long-term EGCG intake come from large meta-analyses of tea consumption, which have reported that side effects are mild [15][16] and can include nausea and upset stomach [13][17].

Three drugs—warfarin (also known as Coumadin™ and Jantoven™), anisindione (or Miradon™), and dicumarol—are known to interact with green tea that contains EGCG, but the interactions are minor [18]. For more information on green tea, please review our separate report.

NOTE: This is not a comprehensive safety evaluation or complete list of potentially harmful drug interactions. It is important to discuss safety issues with your physician before taking any new supplement or medication.

How to Use

A single cup (200 ml) of green or white tea contains 25–200 mg of EGCG [19-21]. Black tea contains much lower levels of EGCG (~20 mg) as it is converted during the oxidation process to thearubigin, a different type of polyphenol [20]. EGCG and other tea catechins are also available as dietary supplements, often in doses of 200–300 mg per serving, which are comparable to doses deemed safe in clinical trials [12][13]. Higher doses can pose health risks, for example to liver function. Clinical trials examining the effects of EGCG on cognitive function have used doses ranging from 9 to 300 mg/day [4].

Learn More

Download full scientific report

An analysis of commercially available green tea supplements at Labdoor

A review of test results on green tea supplements and tea at

Quality Control of Sources: United States Pharmacopeial Convention (USP) and FDA Information on Dietary Supplements offer information on the quality of specific supplements and can assist in finding a trusted brand.


  1. De la Torre R, De Sola S, Pons M et al. (2014) Epigallocatechin-3-gallate, a DYRK1A inhibitor, rescues cognitive deficits in Down syndrome mouse models and in humans. Mol Nutr Food Res 58, 278-288.
  2. De la Torre R, de Sola S, Hernandez G et al. (2016) Safety and efficacy of cognitive training plus epigallocatechin-3-gallate in young adults with Down's syndrome (TESDAD): a double-blind, randomised, placebo-controlled, phase 2 trial. Lancet Neurol 15, 801-810.
  3. Wightman EL, Haskell CF, Forster JS et al. (2012) Epigallocatechin gallate, cerebral blood flow parameters, cognitive performance and mood in healthy humans: a double-blind, placebo-controlled, crossover investigation. Hum Psychopharmacol 27, 177-186.
  4. Scholey A, Downey LA, Ciorciari J et al. (2012) Acute neurocognitive effects of epigallocatechin gallate (EGCG). Appetite 58, 767-770.
  5. Cantero JL, Atienza M, Stickgold R et al. (2003) Sleep-dependent theta oscillations in the human hippocampus and neocortex. J Neurosci 23, 10897-10903.
  6. Mandel SA, Avramovich-Tirosh Y, Reznichenko L et al. (2005) Multifunctional activities of green tea catechins in neuroprotection. Modulation of cell survival genes, iron-dependent oxidative stress and PKC signaling pathway. Neurosignals 14, 46-60.
  7. Ali B, Jamal QM, Shams S et al. (2016) In Silico Analysis of Green Tea Polyphenols as Inhibitors of AChE and BChE Enzymes in Alzheimer's Disease Treatment. CNS Neurol Disord Drug Targets 15, 624-628.
  8. Okello EJ, Savelev SU, Perry EK (2004) In vitro anti-beta-secretase and dual anti-cholinesterase activities of Camellia sinensis L. (tea) relevant to treatment of dementia. Phytother Res 18, 624-627.
  9. Biasibetti R, Tramontina AC, Costa AP et al. (2013) Green tea (-)epigallocatechin-3-gallate reverses oxidative stress and reduces acetylcholinesterase activity in a streptozotocin-induced model of dementia. Behav Brain Res 236, 186-193.
  10. Rezai-Zadeh K, Arendash GW, Hou H et al. (2008) Green tea epigallocatechin-3-gallate (EGCG) reduces beta-amyloid mediated cognitive impairment and modulates tau pathology in Alzheimer transgenic mice. Brain Res 1214, 177-187.
  11. Rasoolijazi H, Joghataie MT, Roghani M et al. (2007) The beneficial effect of (-)-epigallocatechin-3-gallate in an experimental model of Alzheimer's disease in rat: a behavioral analysis. Iran Biomed J 11, 237-243.
  12. Mielgo-Ayuso J, Barrenechea L, Alcorta P et al. (2014) Effects of dietary supplementation with epigallocatechin-3-gallate on weight loss, energy homeostasis, cardiometabolic risk factors and liver function in obese women: randomised, double-blind, placebo-controlled clinical trial. Br J Nutr 111, 1263-1271.
  13. Kumar NB, Pow-Sang J, Egan KM et al. (2015) Randomized, Placebo-Controlled Trial of Green Tea Catechins for Prostate Cancer Prevention. Cancer Prev Res (Phila) 8, 879-887.
  14. Isomura T, Suzuki S, Origasa H et al. (2016) Liver-related safety assessment of green tea extracts in humans: a systematic review of randomized controlled trials. Eur J Clin Nutr 70, 1221-1229.
  15. Hartley L, Flowers N, Holmes J et al. (2013) Green and black tea for the primary prevention of cardiovascular disease. Cochrane Database Syst Rev, CD009934.
  16. Jurgens TM, Whelan AM, Killian L et al. (2012) Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database Syst Rev 12, CD008650.
  17. Dostal AM, Samavat H, Bedell S et al. (2015) The safety of green tea extract supplementation in postmenopausal women at risk for breast cancer: results of the Minnesota Green Tea Trial. Food Chem Toxicol 83, 26-35.
  18. Green tea drug interactions.
  19. Becki (2013) How to get more EGCG from your green tea bag.
  20. (2007) USDA Database for the Flavonoid Content of Selected Foods, Release 2.1 (2007) (PDF). US Department of Agriculture.
  21. Unachukwu UJ, Ahmed S, Kavalier A et al. (2010) White and green teas (Camellia sinensis var. sinensis): variation in phenolic, methylxanthine, and antioxidant profiles. J Food Sci 75, C541-548.