Green tea extract is a concentrated preparation of the leaves of Camellia sinensis, the same plant used for black and oolong tea. Its main active ingredients are catechins, a family of polyphenols, of which epigallocatechin gallate (EGCG) is the most studied. Many extracts also carry caffeine. It is one of the most common ingredients in “fat burner” supplements.
The weight-loss effect is small. A Cochrane review found that green tea preparations produce a small, statistically non-significant weight loss that is unlikely to be clinically important. The more important fact is the safety signal: concentrated extracts have been linked to rare but sometimes severe liver injury, and European regulators concluded in 2018 that daily intakes of 800 mg EGCG or more from supplements raise liver enzymes.
This page summarizes what meta-analyses, clinical trials and regulators (EFSA, USP, LiverTox) report. It is for education only and is not medical advice.
| Property | Detail |
|---|---|
| Type | Botanical extract (dietary supplement in the US; food supplement in the EU) |
| Main actives | Catechins (EGCG, ECG, EGC, EC); caffeine unless decaffeinated |
| EGCG chemistry | C₂₂H₁₈O₁₁, 458.4 g/mol (PubChem) |
| Route | Oral (capsules, tablets, drink powders); one topical prescription drug (Veregen) |
| EGCG in supplements (EU survey) | 5–1,000 mg/day by recommended daily dose |
| Half-life of EGCG | 1.9–4.6 h after single fasting doses of 50–1,600 mg |
| Weight effect | Small and not statistically significant in the Cochrane review |
| Main risk | Idiosyncratic liver injury; enzyme rises at 800 mg EGCG/day or more |
| EU rule | Daily portion must contain under 800 mg EGCG (Regulation (EU) 2022/2340) |
| WADA | Not on the 2026 Prohibited List; caffeine is only monitored |
What it is
Green tea is made by steaming or pan-frying and drying the leaves without fermenting them, while black tea is fermented (NCCIH). Skipping fermentation prevents the polyphenols from oxidizing. EFSA reports that polyphenols make up to 30% of the dry weight of green tea leaves, and that most of these are catechins (EFSA 2018).
The four main catechins are:
- epigallocatechin gallate (EGCG), which EFSA considers the most relevant catechin, including for liver toxicity;
- epicatechin gallate (ECG);
- epigallocatechin (EGC);
- epicatechin (EC).
Green tea leaves also contain caffeine (2.9–4.2% of leaf weight), small amounts of theobromine and theophylline, and the amino acid L-theanine (EFSA 2018). Extracts concentrate these compounds. Some extracts keep the caffeine; others are sold as “decaffeinated” and are standardized mainly to EGCG.
Caffeine and catechin content varies widely
The amount of EGCG and caffeine a person actually gets depends heavily on the product:
| Source | What was found |
|---|---|
| Dried green tea leaves | EGCG 1,600–20,320 mg per 100 g (13-fold range) (EFSA 2018) |
| Brewed green tea | EGCG 2.3–203 mg per 100 g infusion (88-fold range) |
| Green tea drinkers in the EU | Mean 90–300 mg EGCG/day; high consumers up to 866 mg/day |
| EU food supplements | 5–1,000 mg EGCG/day by recommended daily dose |
| Minnesota Green Tea Trial capsules | 843 mg EGCG and 15.8 mg caffeine per day (decaffeinated extract) (Yu et al., 2017) |
Because many fat-loss products also contain caffeine, the caffeine dose matters in its own right. See the caffeine page for its effects and limits.
The one approved drug
The only FDA-approved green tea product is a prescription ointment. Veregen (sinecatechins) 15% ointment is a partially purified water extract of green tea leaves, 85–95% catechins by weight with more than 55% EGCG. It is approved for external genital and perianal warts in immunocompetent adults (Veregen label). It is applied to the skin and has no role in weight loss.
How it works in the body
Two mechanisms are proposed for the fat-loss claims:
- Caffeine on its own raises 24-hour energy expenditure (Hursel et al., Obes Rev 2011).
- Catechins are proposed to add to this by boosting sympathetic (noradrenaline-driven) thermogenesis. In a respiratory chamber study, the extract raised 24-hour urinary noradrenaline excretion by 40%, while the same amount of caffeine alone did not change energy expenditure (Dulloo et al., AJCN 1999).
Absorption and half-life
The oral bioavailability of green tea catechins is low. In plasma, EGCG and ECG appear mostly in the free (unconjugated) form, while EC and EGC appear mostly as glucuronide and sulfate conjugates (Chow et al., 2005).
A single ascending dose study in 60 healthy men gave 94% pure EGCG (50–1,600 mg; 8 men per dose group) or placebo on an empty stomach (Ullmann et al., 2003):
| Parameter | Result across dose groups |
|---|---|
| Time to peak | 1.3–2.2 h |
| Peak plasma EGCG | 130–3,392 ng/mL |
| Total exposure (AUC) | 442–10,368 ng·h/mL |
| Terminal half-life | 1.9–4.6 h |
Fasting vs fed intake
Food sharply lowers how much EGCG reaches the blood. In a crossover study, 30 healthy adults took Polyphenon E (a decaffeinated catechin mixture) at 400, 800 or 1,200 mg EGCG, once fasting and once with a light breakfast (Chow et al., 2005):
- average peak free EGCG was more than 3.5-fold higher when taken fasting;
- mild, short-lived nausea was most common at 1,200 mg and in the fasting condition.
The USP expert panel concluded that repeated bolus doses taken while fasting “significantly” increase EGCG bioavailability, possibly by saturating first-pass elimination. It also noted that people trying to lose weight often eat less, which may mimic fasting (Oketch-Rabah et al., USP 2020). In beagle dogs, fasted animals given a high-EGCG preparation for 13 weeks showed illness and deaths at the higher doses, while fed dogs given recrystallized EGCG did not (the two studies also used different preparations). This is animal data, but it is part of why fasting intake is considered a risk factor.
Taking extract with food is not a guarantee of safety. In the Minnesota Green Tea Trial, the capsules were taken at breakfast and dinner, and liver enzyme rises still occurred (see below).
Regulatory status
- US. Green tea extract is sold as a dietary supplement. Supplements are not approved by the FDA before sale; manufacturers are responsible for safety and labeling (NCCIH). The USP monograph for Powdered Decaffeinated Green Tea Extract requires a label warning: do not take on an empty stomach, take with food, do not use with a liver problem, and stop if symptoms of liver trouble appear. This applies only to products that claim USP compliance (Oketch-Rabah et al., USP 2020).
- EU. Since 2022, green tea extracts containing EGCG are a restricted substance. A daily portion must contain under 800 mg EGCG, and labels must state the EGCG content per portion and warn against use on an empty stomach, with other green tea products on the same day, or by pregnant or breastfeeding women and children under 18. The extracts are also placed under Union scrutiny. Aqueous extracts comparable to traditional tea infusions are excluded (Regulation (EU) 2022/2340).
- Sport. Green tea is not on the WADA 2026 Prohibited List. Caffeine and synephrine are in the 2026 Monitoring Program and are not prohibited.
What the research shows
Weight loss in overweight and obese adults
The 2012 Cochrane review included randomized trials of at least 12 weeks in overweight or obese adults (Jurgens et al., Cochrane 2012). Trials from Japan were too different from the rest to pool, so results were reported separately:
| Outcome | Trials outside Japan (pooled) | Trials in Japan (not pooled, n = 1,030) |
|---|---|---|
| Weight change vs control | −0.04 kg (95% CI −0.5 to 0.4); 6 trials, 532 participants | −0.2 to −3.5 kg |
| BMI change | −0.2 kg/m² (95% CI −0.5 to 0.1) | No effect to −1.3 kg/m² |
| Waist circumference | −0.2 cm (95% CI −1.4 to 0.9) | +1 to −3.3 cm |
| Weight maintenance after loss | No significant effect (2 trials, 184 participants) | — |
The authors concluded that green tea produces a small, non-significant weight loss that is “not likely to be clinically important.”
Other meta-analyses have been somewhat more positive but still show small effects:
- A 2009 meta-analysis of 11 studies found catechins or EGCG-caffeine mixtures reduced body weight by an average of 1.31 kg. The effect appeared smaller in people with high habitual caffeine intake (over 300 mg/day) and in Caucasian vs Asian participants, though neither difference alone reached significance (Hursel et al., IJO 2009).
- A 2024 meta-analysis of 59 randomized trials (3,802 participants) reported significant reductions in body mass, BMI and body fat percentage, but no effect on fat mass. Certainty of evidence ranged from low to high across outcomes (Asbaghi et al., Br J Nutr 2024).
One trial tested a dose above the EFSA threshold: 102 women with central obesity took 856.8 mg EGCG/day or placebo for 12 weeks. Weight in the extract group fell from 76.8 to 75.7 kg, a within-group change of about 1 kg (Chen et al., Clin Nutr 2016). The abstract does not report a between-group difference in weight.
Energy expenditure at rest
In a respiratory chamber, 10 healthy men took a green tea extract (50 mg caffeine and 90 mg EGCG), caffeine alone (50 mg) or placebo at breakfast, lunch and dinner (Dulloo et al., AJCN 1999). Compared with placebo:
- 24-hour energy expenditure rose by 4%;
- the respiratory quotient fell from 0.88 to 0.85, indicating more fat burned;
- caffeine alone at the same dose had no effect.
A meta-analysis of six respiratory-chamber studies found that both catechin-caffeine mixtures and caffeine alone raised 24-hour energy expenditure by about 428–429 kJ (≈ 4.7–4.8%, ≈ 102 kcal). Only the catechin-caffeine mixtures significantly increased 24-hour fat oxidation, by 12.2 g (16.0%) (Hursel et al., Obes Rev 2011). Effects of this size on daily energy expenditure are consistent with the small weight changes seen in longer trials.
Fat oxidation during exercise
Results in exercise studies are mixed, and the larger, longer trials were negative:
| Study | Design | Extract | Result |
|---|---|---|---|
| Venables et al., AJCN 2008 | Crossover, 12 men, 30 min cycling at 60% VO₂max | 366 mg EGCG over the prior 24 h | Fat oxidation 17% higher (0.41 vs 0.35 g/min) |
| Randell et al., MSSE 2013 | Randomized, 31 men, 60 min cycling | 1 or 7 days of extract vs placebo | No change in fat oxidation; 7 days raised plasma fatty acids and glycerol |
| Randell et al., MSSE 2014 | Crossover, 19 active men, 30 min cycling | Decaffeinated extract for 1, 7 or 28 days | No change in fat oxidation or fat-related blood markers at any time point |
The 2008 study also reported a 13% improvement in insulin sensitivity in a separate oral glucose tolerance test in 11 men. Even where fat oxidation rises during a session, this does not by itself translate into meaningful fat loss over time.
Side effects and risks
Liver injury
Liver injury is the main safety concern. LiverTox, the NIH database of drug-induced liver injury, states that green tea extract, and more rarely large amounts of green tea, has been implicated in clinically apparent acute liver injury, including acute liver failure requiring urgent transplantation or causing death (LiverTox).
The US Drug-Induced Liver Injury Network (DILIN) case series. Of 1,414 patients with formally adjudicated liver injury, 40 (3%) were attributed to green tea (Hoofnagle et al., Hepatology 2021):
| Feature | Finding |
|---|---|
| Age | 17–69 years (median 40) |
| Time to symptoms | 15–448 days (median 72) after starting |
| Pattern | Hepatocellular in 95% (marked aminotransferase rises) |
| Jaundice | 83% |
| Severe course | 35% (14 patients) |
| Liver transplant | 8% (3 patients) |
| Chronic injury | 3% |
| Recurrence on re-exposure | 3 patients, with shorter time to onset |
| HLA-B*35:01 carriers | 72% of green tea cases vs 12% of drug cases and 11% of population controls |
The strong link with the immune gene variant HLA-B*35:01 suggests the injury is idiosyncratic and immune-mediated. NCCIH estimates that 5–15% of Americans carry this variant (NCCIH).
The USP review. The USP expert panel found that published case reports associate liver injury with EGCG intakes from about 140 mg to about 1,000 mg/day, with large differences in susceptibility between people. It found no evidence that contaminants such as solvent residues, pesticides, pyrrolizidine alkaloids or heavy metals explained the cases (Oketch-Rabah et al., USP 2020).
The Minnesota Green Tea Trial. This is the largest controlled look at liver effects. Postmenopausal women took a decaffeinated extract providing 843 mg EGCG/day, or placebo, for 12 months (Yu et al., Cancer Prev Res 2017):
| Measure | Result |
|---|---|
| Participants analyzed | 513 extract, 508 placebo |
| ALT rise in extract group | +5.4 U/L (95% CI 3.6–7.1), significantly more than placebo |
| Moderate or worse liver test abnormality | 5.1% (26 women) on extract; odds ratio 7.0 vs placebo (95% CI 2.4–20.3) |
| ALT above 90 U/L (protocol stop) | 36 women on extract vs 4 on placebo |
| Median time to ALT of 90 U/L or more | 106 days (range 56–365) |
Among women who stopped, ALT returned below 90 U/L after a mean of 32 days. Of 20 women who restarted the extract, 11 (55%) had ALT rise above 90 U/L again. This rise-on-rechallenge pattern strongly links the extract to the enzyme changes.
EFSA 2018. After reviewing 38 intervention studies, the EFSA panel concluded that supplement doses of 800 mg EGCG/day or more for 4 months or longer raise ALT and AST in a small share of people, usually under 10%. It found no evidence of liver toxicity below 800 mg/day in trials of up to 12 months, but one product (an 80% ethanolic extract) was linked to liver injury at 375 mg EGCG/day. The panel concluded that it was not possible to identify a dose of EGCG from extracts that could be considered safe. Traditionally brewed green tea, at usual intakes, was considered generally safe (EFSA 2018).
Warning signs listed in the USP label statement include abdominal pain, dark urine and jaundice (yellowing of the skin or eyes).
Multi-ingredient fat burners
Multi-ingredient supplements have become an increasingly common cause of acute liver injury, and green tea is a frequent component of the implicated products (Hoofnagle et al., Hepatology 2021). This makes it harder to assign blame to one ingredient in a given case, although the DILIN investigators found that green tea injury has distinctive clinical features. Combination fat-loss products often also contain stimulants such as caffeine, synephrine or yohimbine, each with its own cardiovascular effects.
Other side effects
NCCIH lists nausea, constipation, abdominal discomfort and increased blood pressure as side effects of green tea extract supplements (NCCIH). Extracts that contain caffeine add caffeine’s effects on sleep, anxiety and heart rate.
Drug interactions
Nadolol. In 10 healthy volunteers, drinking 700 mL/day of green tea for 14 days cut the peak level and total exposure (AUC) of a single 30 mg dose of the beta-blocker nadolol by about 85% (Misaka et al., Clin Pharmacol Ther 2014). The blood-pressure-lowering effect of nadolol was also significantly reduced. The likely mechanism is blockade of the intestinal transporter OATP1A2, which nadolol needs for absorption.
NCCIH also notes that green tea extract can lower blood levels of atorvastatin and has shown an interaction with raloxifene (NCCIH). Anyone taking regular medication should treat concentrated extracts as having interaction potential.
Who should avoid it
Based on the EU label requirements and the USP warning, extracts are flagged as unsuitable for:
- people with existing liver disease;
- pregnant or breastfeeding women;
- children and adolescents under 18;
- use on an empty stomach, or together with other green tea products the same day.
Quality and labeling
Product labels often do not match contents. In an analysis of 19 green tea supplements, only 7 stated their caffeine content, 11 stated EGCG content and 5 stated total polyphenols. The measured contents were inconsistent with label information (Seeram et al., J Agric Food Chem 2006).
EFSA similarly noted that extraction methods change catechin profiles and recommended that labels state catechin content and the proportion of EGCG (EFSA 2018). In the EU this is now required, but in the US a product’s EGCG content may not be stated at all, making it hard to know whether a daily intake is near the levels linked to liver enzyme rises.
Key takeaways
- Weight effect is small. The Cochrane review found a non-significant 0.04 kg difference in trials outside Japan; a 2009 meta-analysis found about 1.3 kg.
- Caffeine does much of the work. Catechin-caffeine mixtures raise daily energy expenditure by about 4–5%, similar to caffeine alone; extra fat oxidation is modest and inconsistent during exercise.
- Liver injury is rare but real. Cases range from enzyme rises to liver failure and transplant, and are strongly linked to the HLA-B*35:01 gene variant.
- Dose and fasting matter. EFSA ties 800 mg EGCG/day or more to liver enzyme rises, and fasting intake raises peak EGCG levels more than 3.5-fold; EFSA could not name a safe extract dose.
- Interactions exist. Green tea cut nadolol exposure by about 85% in a controlled study.
- Labels are unreliable. EGCG and caffeine content vary widely between products and are often not stated.
Sources
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