Green tea extract / EGCG

What it is

Green tea extract is a concentrated preparation of the unfermented leaf of Camellia sinensis. EFSA describes that "Green tea is produced from the leaves of Camellia sinensis (L.) Kuntze, without fermentation, which prevents the oxidation of polyphenolic components. Most of the polyphenols in green tea are catechins." The catechin of interest is EGCG. Crucially, concentration changes the risk picture: EFSA puts habitual EGCG intake from brewed infusions at 90 to 300 mg/day, while "Food supplements containing green tea catechins provide a daily dose of EGCG in the range of 5–1,000 mg/day, for adult population."

What the research says

This is one of the clearest cases in the supplement literature where the harm evidence is stronger than the benefit evidence. A Cochrane review of 18 trials found green tea preparations produce a weight change that is statistically non-significant and too small to matter clinically. A second Cochrane review found green tea does not reduce cancer mortality. Meanwhile the United States Pharmacopeia's causality review of published case reports found 29 cases of liver injury, out of the 35 single-ingredient cases it assessed, that it judged probably, highly likely or definitely caused by green tea extract, LiverTox counts more than 100 published cases of clinically apparent liver injury including fatal liver failure, a 1,075-woman randomised trial found ALT elevations in 6.7% of the extract group versus 0.7% of placebo, and the EU has since capped EGCG in food supplements.

Evidence grade: Not supported by the research.

What goes wrong

Of the 35 single-ingredient green tea extract cases the United States Pharmacopeia review could assess (out of 75 published cases), its experts judged 29 to be probably, highly likely or definitely liver injury caused by the extract. (Source 1)

• Systematic review, Moderate certainty.
• Size: 75 cases published in 51 reports; only the 35 involving single-ingredient green tea extract products were assessed for causality, and 1 of those 35 could not be scored.
• Who: people taking green tea extract products, mostly as supplements.
• How long: case reports accumulated over years; latency typically weeks to months.
• Result: 29 of the 35 single-ingredient cases scored positive by the DILIN method: probably related (14), highly likely (11), definitely related (4)
• Funding: conducted by the United States Pharmacopeia (a standards-setting body) as part of its dietary supplement safety review.

DILIN experts concluded that there was positive liver injury in 29 cases, scoring them as probably related to GTE (14 cases), highly likely related to GTE (11 cases) or definitely related to GTE (4 cases).

The USP review restricted its causality analysis to the 35 of 75 published cases that involved green tea extract as the only ingredient, so the 29 attributed cases are out of 35, not 75. (Source 2)

• Systematic review, Moderate certainty.
• Size: 75 cases published in 51 reports; only the 35 involving single-ingredient green tea extract products were assessed for causality, and 1 of those 35 could not be scored.
• Who: people taking green tea extract products, mostly as supplements.
• How long: case reports accumulated over years; latency typically weeks to months.
• Result: 35 of 75 cases analysed for causality; 40 multi-ingredient cases excluded to remove the effect of other ingredients.
• Funding: conducted by the United States Pharmacopeia (a standards-setting body) as part of its dietary supplement safety review.

To eliminate the possible effects of other ingredients in the involved products, only cases associated with products containing GTE as a single ingredient (35 cases out of 75 cases) were analyzed to determine the causal relationship between the product and hepatotoxicity.

The USP review linked hepatotoxicity to EGCG intakes as low as 140 mg/day and added a cautionary label requirement to its monograph. (Source 3)

• Systematic review, Moderate certainty.
• Size: 75 case reports reviewed, plus animal and human pharmacokinetic data.
• Who: users of green tea extract products.
• How long: not applicable.
• Result: hepatotoxicity associated with EGCG intakes from 140 mg to ~1000 mg/day, with substantial inter-individual variability.
• Funding: United States Pharmacopeia expert panel.

Published adverse event case reports associate hepatotoxicity with EGCG intake amounts from 140 mg to ∼1000 mg/day and substantial inter-individual variability in susceptibility, possibly due to genetic factors.

USP found that taking green tea extract on an empty stomach raises catechin absorption, and required a "take with food" caution. (Source 3)

• Systematic review, Moderate certainty.
• Size: animal and human pharmacokinetic studies reviewed.
• Who: animals and humans given bolus doses of green tea extract.
• How long: repeated dosing studies.
• Result: fasting significantly increases bioavailability of catechins, specifically EGCG, possibly through saturation of first-pass elimination.
• Funding: United States Pharmacopeia expert panel.

Animal and human data indicate that repeated oral administration of bolus doses of GTE during fasting significantly increases bioavailability of catechins, specifically EGCG, possibly involving saturation of first-pass elimination mechanisms.

In a one-year randomised trial of 1,075 postmenopausal women, 6.7% of those taking 843 mg EGCG daily had ALT elevations versus 0.7% on placebo. (Source 4)

• Randomized trial, High certainty.
• Size: 1,075 postmenopausal women.
• Who: predominantly Caucasian postmenopausal women at risk for breast cancer (Minnesota Green Tea Trial)
• How long: 1 year.
• Result: ALT elevation in n=36 (6.7%) of GTE group vs n=4 (0.7%) of placebo (P<0.001); 1.3% had ALT-related serious adverse events; higher nausea (P<0.001) and dermatologic AEs (P=0.05)
• Funding: not stated in the abstract; an academic randomised trial of a breast cancer biomarker endpoint.

More women in the GTE group experienced an alanine aminotransferase (ALT) elevation compared with placebo group (n=36, (6.7%) vs. n=4, (0.7%); P<0.001).

LiverTox records more than 100 published cases of clinically apparent liver injury attributed to green tea extract, including fatal acute liver failure. (Source 5)

• Case series, Moderate certainty.
• Size: more than 100 published cases.
• Who: users of green tea extract and herbal/dietary supplements containing it.
• How long: injury typically arises within 1 to 6 months of starting the product.
• Result: acute hepatitis-like syndrome with markedly hepatocellular enzyme elevations; most recover on stopping but fatal acute liver failure has been described.
• Funding: US National Institute of Diabetes and Digestive and Kidney Diseases (LiverTox)

Nevertheless, more than 100 instances of clinically apparent liver injury attributed to GTE have been reported in the literature.

A green-tea-based weight loss product was withdrawn from Spain and France in 2003, and green tea is an ingredient in over-the-counter weight loss agents implicated in acute liver injury. (Source 6)

• Case series, Low certainty.
• Size: not quantified.
• Who: users of over-the-counter weight loss products containing green tea.
• How long: not applicable.
• Result: regulatory withdrawal of Exolise in 2003; rare instances of clinically apparent acute liver injury linked to multi-ingredient weight loss products.
• Funding: US National Institute of Diabetes and Digestive and Kidney Diseases (LiverTox)

The most prominent regulatory action against green tea containing products concerned Exolise, a weight loss product which was withdrawn from Spain and France in 2003.

The Cochrane cancer review independently recorded liver enzyme elevation among the adverse effects of green tea extract. (Source 7)

• Systematic review, Low certainty.
• Size: 11 randomised trials, 1,795 participants.
• Who: adults in green tea extract trials.
• How long: studies to January 2019.
• Result: no pooled adverse event rate reported; adverse effects listed narratively.
• Funding: not stated.

In addition, adverse effects of green tea extract intake were reported, including gastrointestinal disorders, elevation of liver enzymes, and, more rarely, insomnia, raised blood pressure and skin/subcutaneous reactions.

What the evidence supports

The Cochrane cancer review found a slight quality-of-life improvement with green tea extract in three trials — one of the few positive randomised signals. (Source 7)

• Systematic review, Low certainty.
• Size: 3 experimental studies within the 11 RCTs (1,795 participants total)
• Who: adults in randomised trials of green tea extract versus placebo.
• How long: not stated in the abstract.
• Result: a slight improvement in quality of life compared with placebo; no pooled effect size reported; prostate cancer RR 0.50 (95% CI 0.18 to 1.36), low-certainty.
• Funding: not stated.

Consumption of green tea extracts induced a slight improvement in quality of life, compared with placebo, based on three experimental studies.

What the evidence does not support

A Cochrane review found green tea preparations produce a weight loss that is statistically non-significant and clinically unimportant. (Source 8)

• Systematic review, Low certainty.
• Size: 18 randomised trials (15 weight loss, 3 weight maintenance); 532 participants in the pooled non-Japan weight analysis and 1,030 in the Japanese studies.
• Who: overweight or obese adults.
• How long: trials of at least 12 weeks.
• Result: MD in weight loss -0.04 kg (95% CI -0.5 to 0.4; P = 0.88; I2 = 18%; 532 participants) outside Japan; BMI MD -0.2 kg/m2 (95% CI -0.5 to 0.1; P = 0.21)
• Funding: not stated.

Green tea preparations appear to induce a small, statistically non‐significant weight loss in overweight or obese adults. Because the amount of weight loss is small, it is not likely to be clinically important. Green tea had no significant effect on the maintenance of weight loss.

A Cochrane review of green tea and cancer found no association with cancer mortality and only low-certainty, inconsistent evidence of benefit. (Source 9)

• Systematic review, Low certainty.
• Size: 142 studies: 11 RCTs with 1,795 participants and 131 observational studies with over 1,100,000 participants.
• Who: adults, mostly Asian populations with high habitual green tea intake.
• How long: studies published up to January 2019.
• Result: cancer-related mortality summary RR 0.99, 95% CI 0.91 to 1.07 (8 studies, 504,366 participants, low-certainty); overall cancer incidence summary RR 0.83, 95% CI 0.65 to 1.07 (3 studies, 52,479 participants, low-certainty)
• Funding: not stated.

Conversely, we found no association between green tea consumption and cancer-related mortality (summary RR 0.99, 95% CI 0.91 to 1.07), based on eight studies and 504,366 participants (low-certainty evidence).

The Cochrane cancer review's overall conclusion is that the evidence for a cancer benefit is limited and inconsistent. (Source 10)

• Systematic review, Low certainty.
• Size: 142 studies.
• Who: adults.
• How long: studies to January 2019.
• Result: no reliable pooled benefit; authors note low numbers and small study size as limitations.
• Funding: not stated.

Overall, findings from experimental and nonexperimental epidemiological studies yielded inconsistent results, thus providing limited evidence for the beneficial effect of green tea consumption on the overall risk of cancer or on specific cancer sites.

Where the evidence is mixed

In the same Cochrane review, trials conducted in Japan reported larger weight reductions than trials elsewhere, but were too heterogeneous to pool. (Source 11)

• Systematic review, Very low certainty.
• Size: 8 Japanese trials, 1,030 participants.
• Who: overweight or obese adults in Japan.
• How long: at least 12 weeks.
• Result: weight change ranged from -0.2 kg to -3.5 kg in favour of green tea; BMI reduction ranged from no effect to -1.3 kg/m2.
• Funding: not stated.

The eight studies conducted in Japan were not similar enough to allow pooling of results and MD in weight loss ranged from ‐0.2 kg to ‐3.5 kg (1030 participants) in favour of green tea preparations.

LiverTox notes that drinking brewed green tea, as opposed to taking extracts, has not been associated with liver injury. (Source 12)

• Survey study, Low certainty.
• Size: cross-sectional studies (numbers not given)
• Who: habitual green tea drinkers.
• How long: not applicable.
• Result: regular green tea use associated with lower serum ALT and AST values; in the large prospective trial, ALT elevations in 6.7% vs 0.7% of controls.
• Funding: US National Institute of Diabetes and Digestive and Kidney Diseases (LiverTox)

Drinking green tea has not been associated with liver injury or serum aminotransferase elevations; indeed, cross sectional studies suggest that regular use of green tea is associated with lower serum ALT and AST values.

What official bodies say

EFSA concluded that supplement doses of 800 mg EGCG per day or more raise serum transaminases in clinical trials. (Source 13)

• Official position, Moderate certainty.
• Size: interventional clinical trials reviewed by the EFSA ANS Panel.
• Who: adults in the EU taking green tea catechins as infusions or supplements.
• How long: not applicable.
• Result: doses at or above 800 mg EGCG/day as a supplement produce a statistically significant increase in serum transaminases versus control; infusions deliver 90 to 300 mg/day, high-level consumers up to 866 mg/day.
• Funding: European Food Safety Authority ANS Panel, 2018.

Based on the available data on the potential adverse effects of green tea catechins on the liver, the Panel concluded that there is evidence from interventional clinical trials that intake of doses equal or above 800 mg EGCG/day taken as a food supplement has been shown to induce a statistically significant increase of serum transaminases in treated subjects compared to control.

The European Commission put green tea extracts containing EGCG under restriction in 2022, citing the EFSA finding as indicative of liver injury. (Source 14)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: EU food supplement market.
• How long: in force from 2022.
• Result: a daily portion of food must contain less than 800 mg EGCG; labelling and warning requirements imposed.
• Funding: European Commission regulation.

The Authority also concluded that, based on the available data on the potential adverse effects of green tea catechins on the liver, there is evidence from interventional clinical trials that intake of doses equal to or above 800 mg of (-)-epigallocatechin-3-gallate per day in the form of a food supplement, has been shown to induce a statistically significant increase of serum transaminases in treated subjects compared to control subjects, which is indicative of liver injury.

Where the research disagrees

The dose at which green tea extract becomes hepatotoxic

• EFSA ANS Panel (2018), and the European Commission following it, review of interventional clinical trials: "intake of doses equal or above 800 mg EGCG/day taken as a food supplement has been shown to induce a statistically significant increase of serum transaminases in treated subjects compared to control" (Source 13)
• United States Pharmacopeia Expert Panel (2020), systematic review of case reports with formal causality assessment: "Published adverse event case reports associate hepatotoxicity with EGCG intake amounts from 140 mg to ∼1000 mg/day and substantial inter-individual variability in susceptibility, possibly due to genetic factors." (Source 3)

Whether green tea as a drink carries the same liver risk as concentrated extract

• LiverTox (NIDDK), narrative review citing cross-sectional studies and case series: "Drinking green tea has not been associated with liver injury or serum aminotransferase elevations; indeed, cross sectional studies suggest that regular use of green tea is associated with lower serum ALT and AST values." (Source 12)
• EFSA ANS Panel (2018), review of literature and national authority reports: "However, rare cases of liver injury have been reported after consumption of green tea infusions, most probably due to an idiosyncratic reaction." (Source 13)

How much

• Reference intake: No RDA or adequate intake exists for green tea catechins or EGCG — they are not essential nutrients. EFSA instead reports observed dietary intakes: "The mean daily intake of EGCG resulting from the consumption of green tea infusions ranges from 90 to 300 mg/day while exposure by high‐level consumers is estimated to be up to 866 mg EGCG/day, in the adult population in the EU." (Source 13)
• Upper limit: EFSA (2018) did not set a formal tolerable upper intake level, but the European Commission, restating EFSA's finding in Regulation (EU) 2022/2340, recorded that "intake of doses equal to or above 800 mg of (-)-epigallocatechin-3-gallate per day in the form of a food supplement, has been shown to induce a statistically significant increase of serum transaminases in treated subjects compared to control subjects, which is indicative of liver injury." and placed green tea extracts containing EGCG under restriction on that basis. (Source 14)
• Studied: 843 mg EGCG daily for one year in 1,075 postmenopausal women in the Minnesota Green Tea Trial (Source 4)
• Studied: Cochrane included randomised trials of green tea preparations of at least 12 weeks in overweight or obese adults; doses varied by trial and Japanese and non-Japanese trials were analysed separately (Source 11)
• Studied: Case reports of liver injury span EGCG intakes "from 140 mg to ∼1000 mg/day" (Source 3)

A common belief, and what the research shows

The belief: Green tea extract is a safe, natural fat burner — it is just concentrated tea.

What the research shows: Both halves of that are contradicted by the literature. On efficacy, Cochrane found that "Green tea preparations appear to induce a small, statistically non‐significant weight loss in overweight or obese adults. Because the amount of weight loss is small, it is not likely to be clinically important." On safety, the concentration is exactly the problem: USP's expert panel, assessing the 35 published cases involving single-ingredient extract, found 29 cases of liver injury it scored as "probably related to GTE (14 cases), highly likely related to GTE (11 cases) or definitely related to GTE (4 cases)", LiverTox records that "more than 100 instances of clinically apparent liver injury attributed to GTE have been reported in the literature", and a 1,075-woman randomised trial found that "More women in the GTE group experienced an alanine aminotransferase (ALT) elevation compared with placebo group (n=36, (6.7%) vs. n=4, (0.7%); P<0.001)." Brewed tea is a different exposure: LiverTox notes "Drinking green tea has not been associated with liver injury or serum aminotransferase elevations".

Questions and answers

What is it?

EGCG (epigallocatechin-3-gallate) is the main catechin in green tea. Catechins are the polyphenols of the tea leaf; background sections of research papers note that tea leaves can be up to 30% phenolic substances. Green tea extract supplements concentrate these catechins. (Source 15)

What does it do in the body?

Most of the claimed benefits come from observational studies of tea drinkers, which linked green tea to lower cancer risk and cardiovascular protection. This is background cited by a 2018 pharmacokinetic study, not that study's own result, and observational studies cannot show cause and effect. In that study, peak blood levels of tea catechins varied more than 6-fold between people, which the authors suggest may help explain why both benefits and adverse effects vary. (Source 15)

Is it good or bad for you?

Brewed tea and concentrated extract are different exposures. The Minnesota Green Tea Trial (Yu et al., 2017) randomised 1,075 women to a high-dose green tea extract or placebo for 12 months. Among the 1,021 analysed women with normal liver enzymes at the start, 26 of the 513 in the extract group (5.1%) developed moderate or more severe liver enzyme abnormalities (odds ratio 7.0, 95% CI 2.4 to 20.3). A 2016 systematic review of 34 trials judged liver events after green tea extract to be rare and mostly mild. (Source 16)

How do you get more of it?

EGCG comes from green tea, as a drink or as concentrated extract supplements. The amount that reaches the blood from the same dose is highly variable: in one pharmacokinetic study of green tea extract, peak plasma levels of catechins differed more than 6-fold between people. (Source 15)

If it is harmful, what reduces it?

Where green tea extract has raised liver enzymes, stopping it has reversed the rise. In the Minnesota trial, ALT returned to normal after the extract was stopped and went up again when it was restarted. A 2016 review of 34 trials reported that most liver-related events were mild and none were serious. (Source 16)

Why might someone be low in it or missing it?

Does not apply in the usual sense. EGCG is a plant compound, not an essential nutrient, so there is no deficiency to explain. How much someone takes in depends on the tea they drink. Unoxidised (green) teas are rich in catechins, while fully oxidised (black) teas mostly contain theaflavins and thearubigins. (Source 17)

Which whole foods contain it or feed it?

Green (non-oxidised) tea is the main dietary source. Oolong and black teas are processed by oxidation, which turns much of the catechin content into theaflavins and thearubigins. The Linus Pauling Institute source we fetched named no other food sources. (Source 17)

What happens if you do not have it?

No deficiency state for EGCG is described in the literature we searched. Because it is a non-essential plant compound, people who never drink green tea are not known to develop a specific disease. (Source 15)

We searched: WebSearch on EGCG bioavailability and pharmacokinetics, green tea catechin content, and green tea extract liver safety reviews; none described a deficiency syndrome.

How can you test for it?

No clinical test for EGCG status exists. In research, plasma catechins are measured with HPLC and tandem mass spectrometry, and levels vary widely between people given the same dose. The tests used to monitor harm are standard liver enzyme tests such as ALT, which is how liver problems were detected in the Minnesota trial. (Source 15)

References

1. Toxicology Reports. United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts. 2020. PMID 32140423, DOI 10.1016/j.toxrep.2020.02.008. Read the source
2. Toxicology Reports. United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts. 2020. PMID 32140423, DOI 10.1016/j.toxrep.2020.02.008. Read the source
3. Toxicology Reports. United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts. 2020. PMID 32140423, DOI 10.1016/j.toxrep.2020.02.008. Read the source
4. Food and Chemical Toxicology. The safety of green tea extract supplementation in postmenopausal women at risk for breast cancer: results of the Minnesota Green Tea Trial. 2015. PMID 26051348, DOI 10.1016/j.fct.2015.05.019. Read the source
5. National Institute of Diabetes and Digestive and Kidney Diseases (NIH), NCBI Bookshelf. Green Tea — LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2020. Read the source
6. National Institute of Diabetes and Digestive and Kidney Diseases (NIH), NCBI Bookshelf. Green Tea — LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2020. Read the source
7. Cochrane Database of Systematic Reviews. Green tea (Camellia sinensis) for the prevention of cancer. 2020. DOI 10.1002/14651858.CD005004.pub3. Read the source
8. Cochrane Database of Systematic Reviews. Green tea for weight loss and weight maintenance in overweight or obese adults. 2012. PMID 23235664, DOI 10.1002/14651858.CD008650.pub2. Read the source
9. Cochrane Database of Systematic Reviews. Green tea (Camellia sinensis) for the prevention of cancer. 2020. DOI 10.1002/14651858.CD005004.pub3. Read the source
10. Cochrane Database of Systematic Reviews. Green tea (Camellia sinensis) for the prevention of cancer. 2020. DOI 10.1002/14651858.CD005004.pub3. Read the source
11. Cochrane Database of Systematic Reviews. Green tea for weight loss and weight maintenance in overweight or obese adults. 2012. PMID 23235664, DOI 10.1002/14651858.CD008650.pub2. Read the source
12. National Institute of Diabetes and Digestive and Kidney Diseases (NIH), NCBI Bookshelf. Green Tea — LiverTox: Clinical and Research Information on Drug-Induced Liver Injury. 2020. Read the source
13. EFSA Journal (EFSA Panel on Food Additives and Nutrient Sources added to Food). Scientific opinion on the safety of green tea catechins. 2018. PMID 32625874, DOI 10.2903/j.efsa.2018.5239. Read the source
14. Official Journal of the European Union / EUR-Lex. Commission Regulation (EU) 2022/2340 amending Annex III to Regulation (EC) No 1925/2006 as regards green tea extracts containing (-)-epigallocatechin-3-gallate. 2022. Read the source
15. PLOS ONE. Population nutrikinetics of green tea extract. 2018. DOI 10.1371/journal.pone.0193074. Read the source
16. Cancer Prevention Research. Effect of Green Tea Supplements on Liver Enzyme Elevation: Results from a Randomized Intervention Study in the United States. 2017. Read the source
17. Linus Pauling Institute Micronutrient Information Center, Oregon State University. Tea. Read the source