Green tea extract dosage and evidence
Written by Aaron CuhaReviewed Sep 2026
The short answer
In people, the biggest study gave 1,075 women 843 mg of EGCG a day for a year.
Evidence grade for Green tea extract: Moderate. The rule: at least one finished study in people, and at least 100 people who took it. The sum on this page: 1 completed trial, 1,075 people given it. A grade counts how much has been done to people, not whether it works.
- People given it
- 1,075
- Human studies
- 1
- Found nothing
- 0
Dose
No human dose established
Amounts that were given in studies sit in Human evidence on this page. None of them is a personal dose.
1 completed trial, 1,075 people given it
4 effects reported, 3 unwanted, 1 wanted, by people using it, not a trial
Goal pages: Fat loss and metabolism, Ageing and longevity, Immune system and inflammation, Gut health
In plain English
In plain English, from Aaron
This is how I would explain it to a friend. The evidence, with the numbers, is further down the page.
Green tea extract is a strong dose of the plant compounds in green tea. The main one is called EGCG. Most people buy it for weight loss. It is a supplement, and at high doses it can hurt the liver.
What people take it for
- Weight loss, the main reason.
- Antioxidant support.
- A longer life, after a mouse study.
What studies in people showed
The biggest study gave 1,075 women 843 mg of EGCG a day for a year. A liver damage marker rose in 6.7 percent of them. On a dummy pill it was 0.7 percent. Europe's food safety body says 800 mg a day or more from pills raises liver enzymes. Brewed tea at normal amounts is safe. For weight loss, a review found almost nothing outside Japan, a gap of 0.04 kg. Now mice. By the mouse program's main test, it did not help. A second look found a 7 percent gain in the typical lifespan of females, in midlife only.
What people report
Reports, not study results
The good
- Most people in the liver case reports got better once they stopped the product.
The bad
- Liver injury weeks to months after starting strong extracts. These were often weight-loss products taken on an empty stomach. A few cases were severe.
- Jitters and poor sleep from the caffeine in extracts that are not decaf.
- Nausea. It was the side effect most clearly raised in the one year trial.
Where these come from: Case reports gathered by the US Pharmacopeia and Europe's food safety body, plus the side effect tables of the one year Minnesota trial. We did not find forum reports for this page.
My bottom line
Drink the tea. Skip the pills. The weight loss is close to zero and the liver risk is real at high doses.
An opinion, not a finding. I am a coach, not a doctor.
What it has been measured to do
Measured in people
Goals Green tea extract has been tested for in people, biggest studies first. We count only what the studies on this page say, so the real numbers may be higher.
- Liver fat and liver health1,475 people · 2 studies
- Cancer and tumours1,075 people · 1 study
What people using it report
Real people telling you what happened to them. Nobody checked it, and the people who post are not a fair sample, so it cannot prove anything works. It is still the best guide on this page to what people actually do with Green tea extract, what they expect, and what goes wrong. The full account, including the negative reports, is below.
Animal and lab work, not yet tested in people
Real results, but from animals or cells, not people. What works in a mouse often does not work the same way in a person. Nobody can patent this, so nobody would ever earn back the cost of a study in people. That is usually why there is none. The record on this one is set out below.
- Living longer2 animal or lab studies
33 of the 36 indexed goals have no study of any kind behind Green tea extract
No study in people, animals or cells on this page reports a result for these. That does not prove Green tea extract does nothing for them. It does mean anything you have heard about Green tea extract and one of these did not come from a study cited here.
Show full evidence
What is Green tea extract?
In people, the biggest study gave 1,075 women 843 mg of EGCG a day for a year. Liver blood tests went up in 6.7 percent of them, against 0.7 percent on a dummy pill. A review of weight loss studies found no weight loss that matters. In mice, it did not extend lifespan by the NIA program's standard test. A second look, using a test that counts early deaths more, found a 7 percent gain in typical female lifespan.
Green tea extract is a strong dose of the plant compounds in green tea, called catechins. It is set to a level of EGCG, the main one. Most people buy it for weight loss, or as an antioxidant. It is one of the most used supplements in the United States. It is also the one with the clearest record of liver harm at high doses.
There is enough data in people to say specific things. In the Minnesota Green Tea Trial, 1,075 women past menopause were split by chance. They took an extract with 843 mg of EGCG a day, or a dummy pill, for one year. Side effects overall were about the same (75.6 against 72.8 percent). Nausea was more common on the extract. ALT, a liver damage marker, rose in 36 women on the extract (6.7 percent) against 4 on the dummy pill (0.7 percent). 1.3 percent had a serious problem tied to ALT. Based on this and other trials, the European Food Safety Authority (EFSA) said in 2018 that supplement doses of 800 mg of EGCG a day or more clearly raise liver enzymes. It also said catechins from normal brewed tea are safe at usual amounts. The US Pharmacopeia (USP) reviewed 216 reports of problems with green tea products in 2008. 34 involved liver damage. In 27 the product was a possible cause and in 7 a probable one. Strong extracts taken on an empty stomach were more likely to cause harm. For weight loss, the reason most people buy it, a 2012 Cochrane review looked at studies of 12 weeks or more in overweight or obese adults. In the six studies outside Japan, the difference was 0.04 kg, basically nothing. Eight Japanese studies showed effects from 0.2 to 3.5 kg but could not be combined. The reviewers said the effect was small, could be chance, and was not likely to matter in real life.
In mice, the NIA lifespan program fed green tea extract at 2,000 ppm from 4 months of age. By the standard test, it did not clearly change lifespan in either sex. The authors noted a hint that it might cut midlife deaths in females. The 2024 second look with the Gehan test put a number on that: typical (median) female lifespan up 7 percent, with 129 treated females against 275 untreated. The standard test said this could be chance. The Gehan test said it held up. The survival curves did not fit the standard test's assumptions. Males showed nothing.
Green tea extract is a dietary supplement everywhere this site covers. In the 2000s, France and Spain pulled a weight-loss product containing it over liver concerns. That is what started the USP review.
How does Green tea extract work?
EGCG and the other catechins are plant compounds that act as antioxidants in a dish. In cells they also touch many enzymes and signals. Unless the extract is decaf, it also has caffeine. Caffeine explains much of what people feel, and some of the small calorie-burning effect studied for weight loss. How it harms the liver in people is not fully known. In trials, the harm rises with dose and shows up more when taken on an empty stomach. In a second look at the Minnesota trial, ALT rose more in women who carry one version of a gene (UGT1A4). That gene helps the liver process catechins for removal. The mouse lifespan program picked the extract because it is an antioxidant. Nobody looked into why a midlife signal showed up in females and not males.
What have studies in people found about Green tea extract?
A lot, and mostly about weight and safety, not ageing. Trials add up to several thousand people. The biggest was a one year safety study in 1,075 women. The steady findings: a tiny effect on weight that could be chance, and a rise in liver enzymes at supplement doses of 800 mg of EGCG a day and up, bigger at bigger doses.
- Minnesota Green Tea Trial, 1,075 women past menopause, 843 mg EGCG a day for one year: ALT, a liver damage marker, rose in 6.7 percent against 0.7 percent on a dummy pill. 1.3 percent had a serious problem tied to ALT. Side effects overall were similar, with more nausea on the extract.
- Cochrane review 2012, studies of 12 weeks or more in overweight or obese adults: 0.04 kg difference outside Japan, basically nothing. Japanese studies showed 0.2 to 3.5 kg but could not be combined. No help keeping weight off.
- EFSA 2018: in trials, supplement doses of 800 mg EGCG a day or more clearly raise liver enzymes. Brewed tea at usual amounts is safe.
- USP 2008: 216 reports of problems, 34 involving the liver, 7 with the product a probable cause. Taking it on an empty stomach raises the risk.
- Gene look: in the Minnesota trial, women with one version of the UGT1A4 gene had about two to three times the ALT rise of women without it.
- No trial has measured anything to do with ageing, or deaths, in people taking green tea extract.
What this does not tell you: None of this speaks to how long or how well people live. The liver signal is well shown at high doses, in trials of white women past menopause and in case reports across many groups. How it plays out in men, younger people and lower doses is less clear. The weight loss studies are short and very different from each other. The Japanese studies with bigger effects used products and groups that may not apply elsewhere.
What do people who took Green tea extract report?
This is what real people say happened to them, good and bad. Nobody measured it. A report cannot tell a real effect from the lift people get just from expecting it to work, from a diet or training change made at the same time, or from what was really in the vial. We still put it near the top. It is the next best thing to a study in people: what happens when real people use it, including what goes wrong.
- Case reports gathered by USP and EFSA describe liver injury showing up weeks to months after people started strong extracts. These were often weight-loss products, and often taken on an empty stomach. Most cases got better after the product was stopped. A few were severe.
- The USP review's absorption and animal data point to taking it on an empty stomach as the higher-risk habit. That is the opposite of how weight-loss products are often used.
- Caffeine side effects, jitters and poor sleep, are common with extracts that are not decaf. They come from the caffeine, not the catechins.
- Nausea was the side effect most clearly raised over the dummy pill in the one year Minnesota trial. It also shows up in the case reports as a reason people stop.
Sources: The side-effect 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 side-effect 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.
The state of the research
The National Institute on Aging runs a mouse lifespan program called the Interventions Testing Program. It tests each compound at three labs at the same time: The Jackson Laboratory, the University of Michigan and UT Health San Antonio. The mice are a mixed breed, so a result is less likely to be a quirk of one strain. Males and females are both tested and judged separately. The three labs' results are then pooled. Every result gets published, whether or not the compound worked. It runs on public money from the National Institute on Aging, with no drug company money. Green tea extract was fed at 2,000 ppm from 4 months and reported as a no in both sexes. The original authors noted it might cut midlife deaths in females.
Some results on these pages are called "Gehan-only". That is a weaker claim than "made mice live longer", so it needs explaining. The program's standard test counts every death the same. In 2024 a group at UT Health San Antonio went back over all the program's survival data from 2004 to 2022. That covered 132 compound and sex pairs. They used a second test, called the Gehan test. It gives more weight to deaths that happen young and in midlife. Five compounds that failed the standard test passed this one: metformin, enalapril and 17-DMAG in males, and CAPE and green tea extract in females. The authors say this is the pattern you would expect from something that stops mice dying young and then stops helping. In their words, the effects are "limited to midlife and may not be effective at older ages". They did not report any adjustment for running so many tests at once. So a Gehan-only result means fewer mice died young. By old age the groups caught up, and the oldest mice lived no longer.
For green tea extract, the second look backed up the original authors' hint: a 7 percent gain in typical female lifespan. The Gehan test said it held up. The standard test said it could be chance. The survival curves did not fit the standard test's assumptions. That is a midlife effect in female mice at one dose. It is not a longer life in the program's sense. The human record is unusually useful for a supplement, because a big public safety trial was run. Its main result is a liver warning, not a benefit. That trial happened because green tea extract was being studied to prevent breast cancer, not for longevity. Nobody has paid for a trial of the extract against ageing, and no seller has a reason to. Two European countries pulled a product, and both USP and EFSA wrote formal reviews. That is why this page puts the liver numbers up front, not in a footnote.
The evidence, in charts
Fig. 1a · how many people
1,475people, across 2 studies in people cited here
| Study | People | Share |
|---|---|---|
| Food and Chemical Toxicology 2015 | 1,075 | 73% |
| Journal of Dietary Supplements 2023 | 400 | 27% |
One study holds 73% of these people, so the total rests more on one study than its size suggests. Counts are the number of people each study on this page says it signed up. That includes studies that only watched people and gave nobody the compound. Studies still signing people up are left out, and only studies cited on this page are counted.
Fig. 1b · evidence mix
2 of 7 sources here are studies in people. The rest are not.
- Study in people · done in people229%
- Animal study · done in animals229%
- Review of studies · sums up other studies343%
Counted from the list of sources on this page. It counts only what we cite, so there may be more studies out there. A review counts once, however many studies it sums up.
Fig. 2 · evidence over time
The studies cover 7 different years, 2008 to 2024, counted from the list of sources 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 countries shown. This is what the law says, not a verdict on the science. See Legal status below for the full text and any notes.
Fig. 4 · how much does what
Nobody has tested different amounts in people
This chart would show how the effect changes as the amount goes up. For this compound, nobody has measured that in people. So we leave it empty. We will not borrow an animal chart and pretend it works the same in people.
Fig. 5 · what the molecule is
- Kind of compound
- Supplement
- Molecule weight
- Not on file
- Half-life
- None on file
- Chain length
- None on file
No amino acid sequence is on file for Green tea extract, which is expected: a supplement is not built from amino acids.
The studies we cite
- Study in people2015The safety of green tea extract supplementation in postmenopausal women at risk for breast cancer: results of the Minnesota Green Tea Trial
A year of high dose green tea extract harmed the liver in a small but real share of women. 1,075 women past menopause took an extract with 843 mg of EGCG a day, or a dummy pill, for one year. Liver enzymes rose in 36 women on the extract against 4 on the dummy pill. Just over 1% had a liver problem serious enough to be recorded as such. Nausea and skin reactions were also more common on the extract. The National Cancer Institute paid for it.
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.
- Study in people2023Hepatotoxicity with high-dose green tea extract: effect of catechol-O-methyltransferase and UGT1A4 genotypes
Who gets liver injury from green tea extract may be partly in their genes. This is a second look at the Minnesota trial, covering the 400 women who took the extract. Women carrying one version of a liver-processing gene saw liver enzymes rise about 80% above their starting level at six and nine months. Women with the other version rose about 30%. That is a big difference between people taking the same supplement. It does not tell you which version you carry.
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.
- Review of studies2012Green tea for weight loss and weight maintenance in overweight or obese adults
Green tea does little or nothing for weight. This review looked at studies of 12 weeks or more in overweight or obese adults. Six studies outside Japan, in 532 people, found a difference of 0.04 kg, which could easily be chance. Eight Japanese studies, in 1,030 people, could not be combined. They showed effects from 0.2 to 3.5 kg. It did not help people keep weight off. The reviewers said any effect is small and not likely to matter.
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.
- Review of studies2018Scientific opinion on the safety of green tea catechins
Europe's food safety body says brewed green tea is safe at normal amounts. But in trials, supplements with 800 mg of EGCG a day or more clearly raised liver enzymes compared with people not taking them. Supplements give 5 to 1,000 mg of EGCG a day. Heavy tea drinkers reach up to 866 mg a day.
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.
- Review of studies2008Safety of green tea extracts: a systematic review by the US Pharmacopeia
The US Pharmacopeia looked at 216 reports of problems with green tea products. 34 were about liver damage. In 27 the product was a possible cause, and in 7 a probable one. Strong extracts taken on an empty stomach were more likely to cause harm than when taken with food. The review started after France and Spain pulled a weight-loss product. USP said labels should carry a warning.
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.
- Animal study2024The 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
In mice. A second look at the NIA mouse lifespan program. Green tea extract at 2,000 ppm from 4 months: 129 treated females against 275 untreated ones. Typical female lifespan rose 7 percent. The standard test said that could be chance. The Gehan test, which counts early deaths more, said it held up. Males showed nothing. This was one of 132 comparisons, with no adjustment reported for running so many. The authors say the effect is limited to midlife. Public NIA money paid for it.
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.
- Animal study2013Evaluation of resveratrol, green tea extract, curcumin, oxaloacetic acid, and medium-chain triglyceride oil on life span of genetically heterogeneous mice
In mice. The NIA mouse lifespan program tested five supplements, including green tea extract from 4 months. None clearly made male or female mice live longer by the standard test. A side look hinted the extract might cut midlife deaths in females only. Public NIA money paid for it.
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.
Common questions
Has Green tea extract been tested in people?
Yes. 1,075 people given it across 1 completed trial cited here, 0 of which found nothing. In people, the biggest study gave 1,075 women 843 mg of EGCG a day for a year.
What is the Green tea extract dosage?
No human dose established. Amounts that were given in studies sit in Human evidence on this page. None of them is a personal dose. 1 completed trial, 1,075 people given it
Is Green tea extract FDA-approved?
Not an approved drug. Sold as a dietary supplement. The lifespan hint in female mice comes only from a second look at the data using one statistical test (the Gehan test). Supplement doses of 800 mg EGCG a day or more have been shown to raise liver enzymes, a warning sign for the liver, in controlled studies in people (EFSA 2018).
Did green tea extract extend lifespan in the ITP?
Not by the program's standard test. At 2,000 ppm from 4 months, it made no clear difference in either sex. A 2024 second look used the Gehan test, which counts early deaths more. It found typical female lifespan 7 percent above untreated mice, and said the effect was limited to midlife. Males showed nothing.
Is green tea extract bad for the liver?
At high supplement doses it can be. In 1,075 women taking 843 mg of EGCG a day for a year, 6.7 percent got raised ALT, a liver damage marker, against 0.7 percent on a dummy pill. 1.3 percent had a serious problem tied to ALT. EFSA puts the line for a clear rise in liver enzymes at 800 mg of EGCG a day from supplements. Brewed tea at normal amounts does not carry this warning. Taking strong extracts on an empty stomach seems to raise the risk.
Does it help with weight loss?
Very little, if at all. The Cochrane review of studies lasting 12 weeks or more found a weight difference of 0.04 kg outside Japan. Japanese studies showed bigger effects, but they could not be combined. The reviewers said any effect is small, could be chance, and does not matter in real life.
How much EGCG is in a cup of tea versus a supplement?
EFSA estimates that brewed green tea gives typical drinkers 90 to 300 mg of EGCG a day, and heavy drinkers up to 866 mg. A single supplement can give anywhere from 5 to 1,000 mg a day. The trials that showed liver problems used supplements at 800 mg a day or more.