Green tea extract
Green tea extract (Camellia sinensis catechin concentrate, EGCG-rich)
Written by Aaron CuhaReviewed Sep 2026
Also known as: GTE, EGCG extract, Green tea catechins, Epigallocatechin gallate (principal catechin), Camellia sinensis extract
Did not extend mouse lifespan by the Interventions Testing Program's protocol test; a Gehan reanalysis found a 7 percent female median gain. In people, the largest trial (1,075 women, one year at 843 mg EGCG a day) found liver enzyme elevations in 6.7 percent against 0.7 percent on placebo, and a Cochrane review found no clinically meaningful weight loss.
Overview
Green tea extract is a concentrated catechin preparation, standardised to epigallocatechin gallate (EGCG), sold mainly for weight loss and as an antioxidant. It is one of the most heavily used supplements in the United States and the one with the clearest documented liver injury signal at high doses.
The human record is large enough to say specific things. The Minnesota Green Tea Trial randomised 1,075 postmenopausal women to an extract delivering 843 mg EGCG a day or placebo for one year. Overall adverse event rates were similar (75.6 versus 72.8 percent), nausea was more common on extract, and alanine aminotransferase rose in 36 women on extract (6.7 percent) against 4 on placebo (0.7 percent), with 1.3 percent having an ALT-related serious adverse event. On that and other trials, the European Food Safety Authority concluded in 2018 that supplemental doses at or above 800 mg EGCG a day produce a statistically significant rise in transaminases, while catechins from traditionally brewed tea are safe at usual intakes. The US Pharmacopeia's 2008 review analysed 216 adverse event reports on green tea products, 34 involving liver damage, of which 27 were rated possible and 7 probable causality, and found that concentrated extracts taken on an empty stomach were more likely to cause harm. For the purpose most people buy it, the 2012 Cochrane review of 12-week or longer trials in overweight or obese adults found a weight difference of -0.04 kg (95 percent CI -0.5 to 0.4) in the six studies outside Japan, effects ranging from -0.2 to -3.5 kg in eight Japanese studies that could not be pooled, and concluded the effect was small, not statistically significant and not likely to be clinically important.
In mice, the NIA Interventions Testing Program fed green tea extract at 2,000 ppm from 4 months of age and found no significant effect on lifespan in either sex by log-rank test, noting that a secondary analysis suggested it might reduce midlife deaths in females. The 2024 Gehan reanalysis quantified that: female median lifespan +7 percent (129 treated against 275 controls), log-rank p = 0.37, Gehan p = 0.034, with the proportional hazards assumption violated. Males showed nothing.
Green tea extract is a dietary supplement everywhere this site covers. Regulators in France and Spain suspended a weight-loss product containing it over liver concerns in the 2000s, which triggered the USP review.
Mechanism of action
EGCG and the other catechins are polyphenols with antioxidant activity in vitro and a wide range of enzyme and signalling effects in cell culture; the extract also contains caffeine unless decaffeinated, which accounts for much of what people feel and some of the modest thermogenic effect studied for weight loss. The liver toxicity mechanism in people is not fully established; it is dose-related in trials, more frequent when taken fasted, and in a secondary analysis of the Minnesota trial the rise in ALT was larger in carriers of a UGT1A4 variant, pointing to catechin glucuronidation capacity. The ITP selected the extract for its antioxidant properties. Why a Gehan-only midlife signal appeared in females and not males was not investigated.
Human evidence
Substantial, and mostly about weight and safety rather than ageing. Randomised trials total several thousand participants, the largest a 1,075-woman one-year safety trial. The consistent findings are a small and non-significant effect on body weight and a dose-related rise in liver enzymes at supplemental EGCG doses of 800 mg a day and above.
- Minnesota Green Tea Trial, 1,075 postmenopausal women, 843 mg EGCG a day for one year: ALT elevation 6.7 versus 0.7 percent, 1.3 percent with ALT-related serious adverse events; overall adverse events similar; more nausea on extract.
- Cochrane 2012, trials of 12 weeks or more in overweight or obese adults: -0.04 kg (95 percent CI -0.5 to 0.4) outside Japan; -0.2 to -3.5 kg in unpoolable Japanese trials; no effect on maintaining weight loss.
- EFSA 2018: supplemental doses at or above 800 mg EGCG a day raise transaminases significantly in trials; brewed tea at usual intakes is safe.
- USP 2008: 216 adverse event reports, 34 liver, 7 probable causality; fasting intake raises risk.
- Genetic secondary analysis: UGT1A4 variant carriers in the Minnesota trial showed roughly two to three times the ALT rise of non-carriers.
- No trial has measured any ageing endpoint or mortality in people taking green tea extract.
What this does not tell you: None of this speaks to lifespan or healthspan in people. The liver signal is well documented at high doses in trials of white postmenopausal women and case reports across populations; how it scales to men, younger people and lower doses is less clear. The weight loss trials are short and heterogeneous, and the Japanese trials that showed larger effects used products and populations that may not generalise.
Reading the research record
The NIA Interventions Testing Program runs each compound in parallel at three sites (The Jackson Laboratory, the University of Michigan and UT Health San Antonio) in genetically heterogeneous UM-HET3 mice, tests both sexes, analyses them separately, pools the sites in a site-stratified log-rank test, and publishes every result whether or not the compound worked. It is publicly funded by the National Institute on Aging with no pharmaceutical sponsorship. Green tea extract was fed at 2,000 ppm from 4 months and reported as a null in both sexes, with the original authors noting a possible reduction in midlife deaths in females.
"Gehan-only" needs explaining because it is a weaker and more specific claim than "extended lifespan". The ITP's protocol test is the log-rank test, which weights every death equally and is most sensitive when a treatment lowers mortality by a constant proportion across the whole lifespan. In 2024 a group at UT Health San Antonio reanalysed all ITP survival data from 2004 to 2022, 132 compound by sex comparisons, with the Gehan test, which weights deaths by how many animals are still alive and so gives more weight to early and midlife deaths. Five compounds that had failed the log-rank test passed the Gehan test: metformin, enalapril and 17-DMAG in males, CAPE and green tea extract in females. The authors are explicit that this pattern is what you would expect from a compound that lowers mortality before midlife and then stops helping, that these effects are "limited to midlife and may not be effective at older ages", and no correction for the number of comparisons is reported. A Gehan-only result therefore means: fewer mice died young, the survival curves converged later, and the effect on maximum lifespan was nil.
For green tea extract the reanalysis confirmed the original authors' secondary observation, a 7 percent female median gain that the Gehan test puts at p = 0.034 and the log-rank test at 0.37, with the proportional hazards assumption violated. That is a midlife effect in female mice at one dose, not lifespan extension in the programme's sense. The human record is unusually informative for a supplement because a large publicly funded safety trial was run, and its main result is a liver signal, not a benefit. That trial existed because green tea extract was being studied for breast cancer prevention, not longevity; nobody has funded, and no seller has an incentive to fund, a trial of the extract against an ageing endpoint. The regulatory history, with two European countries suspending a product and both USP and EFSA issuing formal reviews, is the reason this page carries the liver numbers prominently rather than as a footnote.
The evidence, charted
Fig. 1 · evidence composition
2of 7 citations (29%) are in people
Counted from the citation list on this page. The Human count is the same number shown in the badge at the top. Both understate any literature larger than the sources we cite.
Fig. 2 · evidence over time
Evidence spans 7 distinct years, 2008 to 2024, counted from the citation list on this page.
Fig. 3 · legal status at a glance
US
Not approved
UK
Not approved
AU
Not approved
CA
Not approved
Not approved in any of the four jurisdictions shown. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Key studies & citations
- Animal2024
The Gehan test identifies life-extending compounds overlooked by the log-rank test in the NIA Interventions Testing Program: metformin, enalapril, caffeic acid phenethyl ester, green tea extract, and 17-DMAG
Green tea extract 2,000 ppm from 4 months, 129 treated females against 275 controls: median lifespan +7 percent, log-rank p = 0.37, Gehan p = 0.034, proportional hazards assumption violated. No male effect. One of 132 comparisons reanalysed without a reported multiplicity correction; the authors describe the effect as limited to midlife. NIA funded.
GeroScience - Animal2013
Evaluation of resveratrol, green tea extract, curcumin, oxaloacetic acid, and medium-chain triglyceride oil on life span of genetically heterogeneous mice
ITP report: none of the five agents, including green tea extract from 4 months, had a statistically significant effect on lifespan in either sex by log-rank test; a secondary analysis suggested the extract might reduce midlife deaths in females only. NIA funded.
Journals of Gerontology Series A - Human2015
The safety of green tea extract supplementation in postmenopausal women at risk for breast cancer: results of the Minnesota Green Tea Trial
1,075 postmenopausal women randomised to extract with 843 mg EGCG a day or placebo for one year. Adverse events 75.6 versus 72.8 percent; serious 2.2 versus 1.5 percent; more nausea and skin events on extract. ALT elevation in 36 (6.7 percent) versus 4 (0.7 percent), p < 0.001; 1.3 percent had ALT-related serious adverse events. US National Cancer Institute funded.
Food and Chemical Toxicology - Review2012
Green tea for weight loss and weight maintenance in overweight or obese adults
Randomised trials of at least 12 weeks. Six studies outside Japan (532 participants): weight difference -0.04 kg, 95 percent CI -0.5 to 0.4, p = 0.88. Eight Japanese studies (1,030 participants) could not be pooled; effects ranged from -0.2 to -3.5 kg. No effect on weight maintenance. Conclusion: small, not statistically significant, not likely to be clinically important.
Cochrane Database of Systematic Reviews - Review2018
Scientific opinion on the safety of green tea catechins
European Food Safety Authority panel: catechins from traditionally brewed green tea are safe at reported intakes; interventional trials show that supplemental doses at or above 800 mg EGCG a day produce a statistically significant increase in serum transaminases compared with control. Supplements provide 5 to 1,000 mg EGCG a day; high-level tea drinkers reach up to 866 mg a day.
EFSA Journal - Review2008
Safety of green tea extracts: a systematic review by the US Pharmacopeia
216 adverse event case reports analysed, 34 concerning liver damage: 27 rated possible and 7 probable causality by the Naranjo algorithm. Concentrated extracts taken fasted more likely to cause harm than in the fed state. Triggered by French and Spanish suspension of a weight-loss product. USP concluded a caution statement on labelling was warranted.
Drug Safety - Human2023
Hepatotoxicity with high-dose green tea extract: effect of catechol-O-methyltransferase and UGT1A4 genotypes
Secondary analysis of the Minnesota trial (400 women on extract, 98 percent white, mean age 59.8). Mean ALT rose 78 to 82 percent from baseline at months 6 and 9 in UGT1A4 rs6755571 A/C carriers against 28 to 30 percent in C/C, p < 0.001 and p = 0.004. Points to a genetic component in who gets liver injury.
Journal of Dietary Supplements
What users report
Self-reported experiences, not evidence. Nothing below was measured under controlled conditions, and reports like these cannot separate a real effect from placebo, from the training or diet change that accompanied it, or from what the product actually contained. They are here because knowing what people describe, including what goes wrong, is worth reading alongside the studies.
- Case reports compiled by USP and EFSA describe liver injury emerging weeks to months after starting concentrated extracts, frequently products marketed for weight loss and frequently taken on an empty stomach; most cases described resolved after the product was stopped, and a minority were severe.
- The USP review's pharmacokinetic and animal data point to fasted-state intake as the higher-risk pattern, which is the opposite of how weight-loss products are often used.
- Caffeine-attributable effects, jitteriness and disturbed sleep, are a common feature of non-decaffeinated extracts and are not specific to catechins.
- Nausea was the adverse event most clearly increased over placebo in the one-year Minnesota trial and appears in the case report literature as a reason people stop.
Sources: The adverse event case reports analysed in the US Pharmacopeia systematic review (216 reports drawn from the published literature, FDA MedWatch, USP MEDMARX, the Australian TGA, the UK MHRA and Health Canada), the EFSA 2018 opinion's public call for data, and the adverse event tables of the Minnesota Green Tea Trial. No consumer forum or retail review platform was retrieved for this entry, so nothing above is attributed to any forum post.
Frequently asked questions
Did green tea extract extend lifespan in the ITP?
Not by the programme's protocol test: no significant effect in either sex at 2,000 ppm from 4 months. A 2024 reanalysis using the Gehan test, which weights early deaths, found female median lifespan 7 percent above controls at p = 0.034, and describes the effect as limited to midlife. Males showed nothing.
Is green tea extract bad for the liver?
At high supplemental doses it can be. In 1,075 women taking 843 mg EGCG a day for a year, 6.7 percent developed raised ALT against 0.7 percent on placebo, and 1.3 percent had serious ALT-related events. EFSA puts the threshold for a significant transaminase rise at 800 mg EGCG a day from supplements. Brewed tea at normal intakes does not carry this signal. Taking concentrated extracts fasted appears to raise the risk.
Does it help with weight loss?
Very little if at all. The Cochrane review of trials lasting 12 weeks or more found a weight difference of 0.04 kg outside Japan, and larger but unpoolable effects in Japanese trials. The reviewers concluded any effect is small, not statistically significant and not clinically important.
How much EGCG is in a cup of tea versus a supplement?
EFSA estimates that brewed green tea provides 90 to 300 mg EGCG a day for typical drinkers and up to 866 mg for heavy drinkers, while supplements range from 5 to 1,000 mg a day in a single product. The trials with liver signals used supplements at or above 800 mg a day.