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green tea leaves

© 2018 Steven Foster

A green tea monograph for the home

Latin Name: Camellia sinensis

Common Name: green tea

This green tea monograph provides basic information about green tea—common names, usefulness and safety, and resources for more information.


Green Tea Basics

  • Green, black, and oolong teas all come from the same plant, Camellia sinensis, but are prepared using different methods. To produce green tea, fresh leaves from the plant are lightly steamed.
  • Tea has been used for medicinal purposes in China and Japan for thousands of years.
  • Current uses of green tea as a beverage or dietary supplement include improving mental alertness, relieving digestive symptoms and headaches, and promoting weight loss. Green tea and its extracts, such as one of its components, EGCG, have been studied for their possible protective effects against heart disease and cancer.
  • Green tea is consumed as a beverage. It is also sold in liquid extracts, capsules, and tablets and is sometimes used in topical products (intended to be applied to the skin).

Green Tea in Health Research

  • Although many studies have been done on green tea and its extracts, definite conclusions cannot yet be reached on whether green tea is helpful for most of the purposes for which it is used.

Green Tea Health Summary

  • There’s evidence that green tea enhances mental alertness, as would be expected because of its caffeine content.
  • The U.S. Food and Drug Administration has approved a specific green tea extract ointment as a prescription drug for treating genital warts.
  • Studies of green tea and cancer in people have had inconsistent results. The National Cancer Institute does not recommend for or against using green tea to reduce the risk of any type of cancer.
  • Very few long-term studies have investigated the effects of tea on heart disease risk. However, the limited evidence currently available suggests that both green and black tea might have beneficial effects on some heart disease risk factors, including blood pressure and cholesterol.
  • Green tea extracts haven’t been shown to produce a meaningful weight loss in overweight or obese adults. They also haven’t been shown to help people maintain a weight loss.
  • The National Center for Complementary and Integrative Health (NCCIH) is funding research on green tea and its extracts, including studies of the effects of high doses of tea components on the liver, whether substances in green tea can be helpful for iron overload disease, and the safety of a component of green tea in people who are HIV-positive.

Green Tea Safety

  • Green tea, when consumed as a beverage, is believed to be safe when used in moderate amounts.
  • Liver problems have been reported in a small number of people who took concentrated green tea extracts. Although the evidence that the green tea products caused the liver problems is not conclusive, experts suggest that concentrated green tea extracts be taken with food and that people discontinue use and consult a health care provider if they have a liver disorder or develop symptoms of liver trouble, such as abdominal pain, dark urine, or jaundice.
  • Except for decaffeinated green tea products, green tea and green tea extracts contain substantial amounts of caffeine. Too much caffeine can make people feel jittery and shaky; interfere with sleep; and cause headaches.
  • Green tea has been shown to reduce blood levels (and therefore the effectiveness) of the drug nadolol, a beta-blocker used for high blood pressure and heart problems. It may also interact with other medicines.

Green Tea References


PubMed Articles About Camellia sinensis

Source: National Center for Biotechnology Information (NCBI)[Internet]. Bethesda (MD): National Library of Medicine (US), National Center for Biotechnology Information; [1988] – [cited 2018 Apr 5]. Available from:

Sánchez, M., González-Burgos, E., Iglesias, I., Lozano, R., Gómez-Serranillos, MP., (2021) The Pharmacological Activity of (‎L.‎) ‎Kuntze‎ on Metabolic and Endocrine Disorders: A Systematic Review.

Tea made from leaves is one of the most consumed beverages worldwide. This systematic review aims to update pharmacological activity on metabolic and endocrine disorders. Inclusion criteria were preclinical and clinical studies of tea extracts and isolated compounds on osteoporosis, hypertension, diabetes, metabolic syndrome, hypercholesterolemia, and obesity written in English between 2014 and 2019 and published in Pubmed, Science Direct, and Scopus. From a total of 1384 studies, 80 reports met inclusion criteria. Most papers were published in 2015 (29.3%) and 2017 (20.6%), conducted in China (28.75%), US (12.5%), and South Korea (10%) and carried out with extracts (67.5%, especially green tea) and isolated compounds (41.25%, especially epigallocatechin gallate). Most pharmacological studies were and studies focused on diabetes and obesity. Clinical trials, although they have demonstrated promising results, are very limited. Future research should be aimed at providing more clinical evidence on less studied pathologies such as osteoporosis, hypertension, and metabolic syndrome. Given the close relationship among all endocrine disorders, it would be of interest to find a standard dose of tea or their bioactive constituents that would be beneficial for all of them.

Filippini, T., Malavolti, M., Borrelli, F., Izzo, AA., Fairweather-Tait, SJ., Horneber, M., Vinceti, M., (2021) Green tea (Camellia sinensis) for the prevention of cancer.

This review is an update of a previously published review in the Cochrane Database of Systematic Reviews (2009, Issue 3).Tea is one of the most commonly consumed beverages worldwide. Teas from the plant Camellia sinensis can be grouped into green, black and oolong tea, and drinking habits vary cross-culturally. C sinensis contains polyphenols, one subgroup being catechins. Catechins are powerful antioxidants, and laboratory studies have suggested that these compounds may inhibit cancer cell proliferation. Some experimental and nonexperimental epidemiological studies have suggested that green tea may have cancer-preventative effects.

Hashempur, MH., Sadrneshin, S., Mosavat, SH., Ashraf, A., (2019) Green tea (Camellia sinensis) for patients with knee osteoarthritis: A randomized open-label active-controlled clinical trial.

Green tea is known as a dietary supplement and a novel functional food worldwide. Since there are increasing preclinical evidence about efficacy of green tea for treating osteoarthritis, this study has aimed at assessing its efficacy and safety for patients with knee osteoarthritis.

Doustfatemeh, S., Imanieh, MH., Mohagheghzade, A., Zarshenas, MM., Torkamani, Z., Yousefi, G., Farahangiz, S., Salehi, A., (2018) The Effect of Black Tea (Camellia sinensis (L) Kuntze) on Pediatrics With Acute Nonbacterial Diarrhea: A Randomized Controlled Trial.

We aimed to evaluate the antidiarrheal effect of black tea in pediatric patients with acute nonbacterial diarrhea. This single-blind randomized clinical trial study was performed on 2 to 12-year-old patients, with acceptable criteria for acute nonbacterial diarrhea in Shiraz, Iran. In total, 120 patients took part in this study. Blocked randomization method was used to allocate them into 2 groups of intervention (black tea tablet + standard treatment) and control group (standard treatment; 60 patients in each). Frequency of defecation, volume, and consistency of stool were registered on arrival and 24 hours later. We used χ test, t test, and Mann-Whitney U test. After a 24-hour follow-up, the proportion of patients with formed stool was higher in the intervention group when compared with the control group (P < .001). There was a significant difference between the mean number of defecations per 24 hours in both groups, after treatment (P < .001). We found a possible antidiarrheal effect of black tea.

Maeda-Yamamoto, M., Nishimura, M., Kitaichi, N., Nesumi, A., Monobe, M., Nomura, S., Horie, Y., Tachibana, H., Nishihira, J., (2018) A Randomized, Placebo-Controlled Study on the Safety and Efficacy of Daily Ingestion of Green Tea ( L.) cv. "Yabukita" and "Sunrouge" on Eyestrain and Blood Pressure in Healthy Adults.

The green tea ( L.) cultivar “Sunrouge” contains anthocyanins, catechins and flavonols. To determine whether ingesting green tea containing anthocyanins improves visual function and blood pressure (BP) in healthy adults, a randomized, double-blind, placebo-controlled study was performed. A total of 120 healthy subjects, aged between 20 and 60 years and with a systolic BP (SBP) value of ≤125 and <155 and a diastolic BP (DBP) value <95, or a DBP of ≤75 mmHg and <95 mmHg and a SBP <155 mmHg, were randomly assigned to one of three groups. For 12 weeks, the placebo group received barley extract without catechin; another group received “Sunrouge” extract containing 11.2 mg anthocyanin and 323.6 mg epigallocatechin-3--gallate (EGCG); and a third group received “Yabukita” extract containing 322.2 mg EGCG. Home BP, accommodation ability, visual analog scale questionnaires for eyestrain, and metabolic-associated markers were analyzed at weeks 0, 4, 8, and 12 of the intake period. The ingestion of “Sunrouge” tea significantly improved accommodation ability and eyestrain in subjects younger than 45 years and in subjects who operated visual display terminals every day. It also elevated BP. “Yabukita” tea ingestion significantly increased serum adiponectin levels. No adverse effects were observed. We conclude that long-term intake of “Sunrouge” tea containing anthocyanins and flavonols might improve visual function.