Green Tea's Paper Trail, From Origin Stories to EGCG Capsules
One green tea plant gives a cup that EFSA calls generally safe and a supplement that EFSA links to early liver damage signs at 800 mg of EGCG a day. This history follows the plant from Tang-dynasty tea writing to the trials, case registries and regulators that now shape the labels.
Jump to: - [Medicine came before the cup](#medicine-came-before-the-cup) - [A Japanese monk's tea book and a shogun's hangover](#a-japanese-monks-tea-book-and-a-shoguns-hangover) - [The dose is where the story changes](#the-dose-is-where-the-story-changes) - [Weight trials found small, uneven changes](#weight-trials-found-small-uneven-changes) - [The liver warning comes from case reports and registries](#the-liver-warning-comes-from-case-reports-and-registries) - [What regulators did with the numbers](#what-regulators-did-with-the-numbers) The history of green tea is a story about dose as much as leaves. One plant gives a cup that the European Food Safety Authority (EFSA) calls generally safe, and a supplement that EFSA links to possible early signs of liver damage at 800 mg of EGCG a day. The plant is the same. What changes is how much EGCG a person takes in, and how. The early sources describe tea in general. The modern ones are mostly trials and safety reviews of concentrated extracts. ## Medicine came before the cup The Smithsonian's National Museum of Asian Art (Freer and Sackler) says tea was first used as medicine in ancient times. It became a popular beverage during the Tang dynasty, when Lu Yu wrote the first known book on tea, *The Classic of Tea*. [Smithsonian](https://asia-archive.si.edu/learn/for-educators/teaching-china-with-the-smithsonian/videos/exploring-chinese-teas-and-tea-wares/) The National Center for Complementary and Integrative Health (NCCIH) says the tea plant was first cultivated in China thousands of years ago, and that there is evidence of tea being used for health purposes about 3,000 years ago. [NCCIH](https://www.nccih.nih.gov/health/green-tea) Some accounts reach further back. A 2023 editorial in *Foods*, "Advances in Tea Chemistry," says the origins of tea "can be traced back to the Shennong period." According to PubMed, the abstract as indexed cites no source for that date, so this article treats it as a claim rather than a record. [DOI](https://doi.org/10.3390/foods12213944) ## A Japanese monk's tea book and a shogun's hangover One early Japanese tea text has a named author: Eisai (1141 to 1215), a Buddhist priest who had studied in China. In his later years he wrote *Kissa Yōjōki*, which the library's English title renders as *Drink Tea and Prolong Life*. The Tōyō Bunko in Tokyo dates its compilation to 1211 and its printing to 1694. Volume one covers types of tea, how to make green tea, and tea's medicinal effects. [Tōyō Bunko](https://toyo-bunko.or.jp/wp-content/uploads/2024/03/f4132910852d33e4a936373066effadc.pdf) The same exhibit note cites the *Azuma Kagami*, a chronicle it dates to about 1300. It records that the third Kamakura shogun, Minamoto no Sanetomo, was suffering from a hangover, and that he quickly recovered after Eisai presented tea. The sources do not say how tea plants or seeds reached Japan, so this article does not claim a route. ## The dose is where the story changes EFSA's 2018 assessment followed concerns from Nordic countries about reported liver damage possibly linked to green tea products. It treated the drink and the supplement differently. EGCG is the most abundant catechin in green tea, and EFSA estimates that traditional infusions supply 90 to 300 mg of it a day on average. [EFSA](https://www.efsa.europa.eu/en/press/news/180418) Adults who drink large quantities may reach 866 mg. That is the surprise. A heavy tea drinker can reach the 800 mg level that EFSA links to supplements, and EFSA still rated infusions generally safe. It pointed to how the two are taken. Tea is usually drunk with food and spread through the day, while supplements, "especially for slimming," are more often taken on an empty stomach as one daily dose. Extracts add another variable. A 2020 U.S. Pharmacopeia review says animal and human data show that repeated bolus doses taken during fasting significantly raise catechin bioavailability, especially EGCG. [DOI](https://doi.org/10.1016/j.toxrep.2020.02.008) The [collagen history](/blog/history/history-of-collagen-from-boiled-bones-to-peptides) traces the same move from boiled bone to capsule, and the [vitamin C history](/blog/history/history-of-vitamin-c-from-scurvy-to-ascorbic-acid) covers the 1932 identification of the compound behind citrus's cure. ## Weight trials found small, uneven changes The 2012 Cochrane review by Jurgens and colleagues pooled green tea trials in adults with overweight or obesity. Outside Japan, six trials with 532 participants showed a difference of 0.04 kg that was not statistically significant. The eight Japanese trials showed reductions from 0.2 kg to 3.5 kg, but they were too different to pool. The authors called the overall loss "not likely to be clinically important." The trials also reported two hospitalizations in green tea groups, which they did not link to the tea. [DOI](https://doi.org/10.1002/14651858.CD008650.pub2) Baladia and colleagues pooled five randomized trials of at least 12 weeks in 301 adults with a BMI of 25 to 40. Their weight result was a mean loss of 0.78 kg that was not statistically significant. A small fall in body fat percentage was statistically significant, but the authors called it not clinically relevant. The article is in Spanish. [DOI](https://doi.org/10.3305/nh.2014.29.3.7118) Kapoor and colleagues looked at energy use instead of the scale. Across eight randomized trials, EGCG supplements raised energy expenditure by about 158 kJ a day compared with placebo, and the change in fat oxidation did not reach significance. The authors asked for "large prospective trials." Two of their four authors list Taiyo Kagaku Co. Ltd. as an affiliation. [DOI](https://doi.org/10.1016/j.jnutbio.2016.10.013) For the cell-level side of that energy story, the [mitochondrial health guide](/health/mitochondrial-health-complete-guide) explains how mitochondria turn the energy in food into ATP. ## The liver warning comes from case reports and registries NCCIH calls liver injury uncommon. It has been reported in some people who used green tea products, mostly extracts in tablets or capsules. NCCIH says people with a specific variant of an immune-related gene appear more susceptible, and that 5 to 15 percent of Americans carry it. [NCCIH](https://www.nccih.nih.gov/health/green-tea) A 2021 study from the U.S. Drug-Induced Liver Injury Network reviewed 1,414 patients and attributed 40 cases (3 percent) to green tea. HLA-B*35:01 appeared in 72 percent of the green tea cases, compared with 15 percent of other-supplement cases and 12 percent of drug cases. Fourteen of the 40 green tea cases were severe, and three patients needed a liver transplant. [DOI](https://doi.org/10.1002/hep.31538) Navarro and colleagues wrote in 2017 that green tea extract and many other products "tend to cause an acute hepatitis-like injury." [DOI](https://doi.org/10.1002/hep.28813) The U.S. Pharmacopeia's 2020 review found published case reports linking liver injury to EGCG intakes from 140 mg to about 1,000 mg a day, with large differences between people that may be genetic. It found no evidence that solvent residues, pesticide residues, pyrrolizidine alkaloids, or elemental impurities caused the injury. [DOI](https://doi.org/10.1016/j.toxrep.2020.02.008) Not every reviewer reads the cases the same way. Teschke and colleagues (2014) found no clinical evidence that green tea extract raises the risk of liver injury from drugs taken at the same time, though they reported lab-level enzyme inhibition. [DOI](https://doi.org/10.1517/17425255.2014.971011) ## What regulators did with the numbers EFSA called for more studies on green tea catechins and clearer labels stating catechin content and possible health risks on supplements. It sent its advice to the European Commission, which decides the follow-up. [EFSA](https://www.efsa.europa.eu/en/press/news/180418) In the United States, the FDA has approved a prescription ointment containing a specific green tea extract for external genital and perianal warts, according to NCCIH. Dietary supplements, by contrast, are not approved by the FDA before they are sold, and manufacturers are responsible for their safety and labeling. [NCCIH](https://www.nccih.nih.gov/health/green-tea) The U.S. Pharmacopeia added a cautionary labeling requirement to its monograph for powdered decaffeinated green tea extract. [DOI](https://doi.org/10.1016/j.toxrep.2020.02.008) ## Bottom line A cup of green tea has no safety concern that NCCIH reports for adults, apart from caffeine. Concentrated EGCG is a different product. EFSA could not identify a safe dose for supplements, and it flagged 800 mg a day. Read the EGCG amount per serving, and if you take nadolol, atorvastatin or raloxifene, talk with your clinician, because NCCIH describes interactions with all three. ## Frequently asked questions ### What are catechins, and why does EGCG get singled out? Catechins are substances naturally present in green tea. EGCG (epigallocatechin gallate) is the most abundant, according to EFSA. Kapoor and colleagues call EGCG "thought to be the most pharmacologically active" catechin, and say it "has been studied extensively." [DOI](https://doi.org/10.1016/j.jnutbio.2016.10.013) ### How much EGCG is in a cup of green tea? EFSA's daily average for traditional infusions is 90 to 300 mg of EGCG, with up to 866 mg for adults who drink large quantities. That is a daily total from all the tea a person drinks, not a per-cup figure. ### Is green tea safe to drink? NCCIH reports no safety concerns for green tea consumed as a beverage by adults, though it contains caffeine. EFSA reached the same view for infusions. ### Can green tea extract harm the liver? Rarely. NCCIH calls liver injury uncommon and mostly tied to extracts in tablets or capsules. EFSA says 800 mg of EGCG a day from supplements may be associated with initial signs of liver damage. ### Does green tea help with weight loss? The trials show small effects at most. The 2012 Cochrane review found a loss that was not statistically significant, and its authors called it not likely to be clinically important. ### How did tea reach Japan through Buddhist monks? The sources show a monk's book on tea compiled in 1211, but not how tea reached Japan. This article does not claim a route. ## Next reads - [Mitochondrial health guide](/health/mitochondrial-health-complete-guide): the cell-level energy background behind the energy-expenditure trials above. - [History of turmeric and curcumin](/blog/history/history-of-turmeric-and-curcumin-from-ayurveda-to-isolation): the same move from a whole plant to one group of compounds inside it, with each date tied to its source. ### Related reading - [the ginseng history, from Shennong to American export](/blog/history/history-of-ginseng-from-shennong-to-american-export) - [the resveratrol history, from hellebore to the French paradox](/blog/history/history-of-resveratrol-from-hellebore-to-french-paradox)