Green Tea Extract

Short answer

Green tea extract is a supplement in which tea catechins are presented in concentrated form such as a capsule, tablet, or powder; it is different from brewed tea. EFSA reports that EGCG at 800 mg per day and above as a supplement increases serum transaminases (liver enzymes); no EGCG dose that could be considered “safe” could be established from extracts. ^[1] The “margin of safety” approach that applies to brewed green tea does not apply to extracts. ^[1]

What is green tea extract, and how does it differ from brewed tea?

Green tea extract is a concentrated form of the catechins (especially EGCG) in green tea leaves. EFSA states that green tea catechins can be taken in three forms: a traditional infusion, a ready-to-drink beverage of equivalent composition, and a supplement containing a concentrated extract. Supplements provide 5–1,000 mg of EGCG per day in adults; EGCG from green tea infusion consumption in the EU is on average 90–300 mg per day, and up to 866 mg in high consumers. ^[1]

EFSA reports that catechins in extracts may be more concentrated than in the beverage and that the composition and manner of consumption may differ. ^[1] Green tea composition varies greatly with plant variety, growing environment, season, leaf age, and production conditions: EGCG ranges from 1,600 to 20,320 mg/100 g in dry leaf and 2.3 to 203 mg/100 g in infusion. ^[1] The phrase “green tea extract” on a label therefore does not by itself show how much EGCG is taken; the EU regulation (below) requires the amount of EGCG per serving to appear on the label for this reason.

The Turkish Food Codex Communiqué on Food Supplements (Türk Gıda Kodeksi Takviye Edici Gıdalar Tebliği, No. 2013/49) defines a food supplement as a product of concentrates or extracts of herbal substances and bioactive substances with a nutritive or physiological effect, in forms such as capsules, tablets, lozenges, single-use powder sachets, liquid ampoules, dropper bottles, or similar, with a defined daily intake dose. ^[6] Capsules and tablets containing green tea extract may fall within this definition. According to the 2013 text of the Communiqué, the label, presentation, or advertising of these products may not carry statements claiming a property of preventing, treating, or curing a disease; the label carries the statements “Not a medicine. Not used for the prevention or treatment of diseases.” (“İlaç değildir. Hastalıkların önlenmesi veya tedavi edilmesi amacıyla kullanılmaz.”) and “Consult your doctor during pregnancy and breastfeeding and if there is a disease or medicine use.” (“Hamilelik ve emzirme dönemi ile hastalık veya ilaç kullanılması durumlarında doktorunuza danışın.”). ^[6] The Communiqué was amended later.

Does green tea extract harm the liver?

EFSA’s 2018 opinion is the basic source for this question. ^[1]

• Dose–effect. In intervention studies, EGCG at 800 mg per day and above as a supplement led to a statistically significant increase in serum transaminases in the treatment group compared with control. Examining 38 intervention studies, EFSA stated that use of extracts containing EGCG at 800 mg per day and above for 4 months or longer was associated with ALT and AST elevations in a small percentage of the population (generally less than 10%).
• Numbers. 84 cases of transaminase elevation were reported in 880 people treated with EGCG at 800 mg/day and above; no cases were reported in 756 people treated with EGCG at 316 mg/day or below. In one study, moderate or more severe liver function abnormality was seen at a rate of 5.1% in more than 500 people treated for one year with 843 mg EGCG per day.
• Below 800 mg. In intervention studies, no transaminase elevation was reported at doses below 800 mg per day for 2 weeks to 12 months; however, EFSA also states that these studies did not have enough power to detect effects at the percent level. No “safe dose of EGCG” below 800 mg per day as green tea extract could be established.
• Exception: a single product. In 2003 a weight-loss product was withdrawn from the market after 13 cases of liver toxicity in Spain and France. For this product, which contained an 80% ethanolic extract, serious liver injury was reported at a dose corresponding to 375 mg EGCG per day; EFSA assessed this as most likely an idiosyncratic reaction.
• Case reports. Cases of liver injury have been seen across a wide dose range, from consumption exceeding three cups of green tea infusion to 1,800 mg of extract per day; the amount of EGCG was not stated in most cases.

NCCIH reports that liver injury is rare but has been reported mainly with green tea extracts in tablet or capsule form, and that people carrying a specific immune-related gene variant appear particularly susceptible (5–15% of Americans). ^[2] The Cochrane cancer review also states that digestive disorders and increases in liver enzymes, and more rarely insomnia, increased blood pressure, and skin reactions, were reported in studies using green tea extract. ^[3]

Does green tea extract on an empty stomach increase the risk?

According to human data, EFSA states that giving green tea extract fasting and as a single bolus dose significantly increased the area under the plasma concentration–time curve (AUC) of EGCG compared with giving it with food and in divided doses. When 800 mg EGCG per day was given with food as a single dose for 10 days or more, systemic EGCG exposure also increased; this increase is not marked when the dose is divided into two of 400 mg; the mechanism is not understood. ^[1]

On this basis, the 2022 Commission Regulation in the EU (2022/2340) requires that the daily serving of foods containing green tea extract contain less than 800 mg of EGCG; the label must show the maximum number of servings that can be consumed daily, the warning that 800 mg or more of EGCG per day should not be consumed, and the amount of EGCG per serving, and must also carry a warning that the product should not be consumed by people consuming other products containing green tea on the same day, as well as these warnings: “should not be consumed by pregnant or breastfeeding women and children under 18 years of age,” and “should not be consumed on an empty stomach.” The regulation’s rationale rests on EFSA’s findings that fasting increased the toxicity of green tea catechins in experimental animals and that no intervention study examined pregnant, breastfeeding, infant, and under-18 groups. Aqueous extracts reconstituted with a composition similar to green tea infusion are outside this scope. The regulation also placed these extracts on the EU list of “substances under scrutiny,” because the possibility of harm and scientific uncertainty persist at intakes below 800 mg per day. ^[8] This is an EU regulation; it does not apply automatically in Türkiye. Türkiye’s own limit is in the Ministry of Agriculture and Forestry’s Restricted Substances List (21/09/2026): for purified EGCG extract obtained from green tea leaves (on condition that it complies with Annex 1 of the Turkish Food Codex Novel Foods Regulation), 150 mg of extract per unit and a maximum of 300 mg of extract per day, identically in the 4–10 and 11-and-over columns; the label carries a statement that consumers should not consume more than 300 mg of extract per day (03/07/2026). For green tea extract containing non-isolated EGCG (“other sources”; not assessed as a novel food if its use in food supplements before 31/12/2025 is proven), the limit is 540 mg/day together with or separately from other catechins (age 11 and over). ^[9] The limits in Türkiye are written as the amount of extract or total catechins; the EU’s 800 mg limit is the amount of EGCG in a serving. The two numbers are not in the same unit and cannot be converted into each other.

Does green tea extract affect iron absorption?

Ullmann et al. (2005), in a randomized, double-blind, placebo-controlled, three-period crossover study in 30 healthy women with low iron stores, measured the effect of pure crystalline EGCG (150 mg, 300 mg, or placebo; each for 8 consecutive days, with a 14-day washout between) on non-heme iron absorption. Relative to placebo, absorption decreased by 14% with 150 mg EGCG and by 27% with 300 mg EGCG; the difference was significant between placebo and 300 mg and between 150 mg and 300 mg. The authors stated that the effect was much smaller than that reported for black tea, that supplements at the time would contain lower EGCG than the doses in the study, and that no health-relevant effect was expected with normal iron stores; the first author worked in the research unit of a vitamin company that produces pure EGCG. ^[4] Because EFSA now reports that supplements can provide 5–1,000 mg of EGCG per day ^[1], products exceeding the 300 mg dose in the study may exist; iron absorption was not measured for these doses.

Does green tea cause drug interactions?

Misaka et al. (2020), in a randomized, three-phase crossover study in 11 healthy volunteers, gave the beta blocker nadolol with water, with co-brewed green tea (150 mL), or with green tea drunk 1 hour before nadolol. The nadolol AUC0–48 was found to be 0.371 (90% CI 0.303–0.439) of the water value when taken with green tea, and 0.536 (0.406–0.665) when green tea was drunk 1 hour earlier; the time to reach maximum concentration and renal clearance did not differ between groups. The authors state that a single drink of green tea markedly lowered nadolol plasma levels and that the effect may last at least 1 hour. ^[5] What was used in this study is not an extract but brewed tea; the interaction thus applies to the beverage too.

NCCIH also reports that green tea extract can reduce the blood level of the cholesterol drug atorvastatin and that there is an interaction with raloxifene (an osteoporosis drug). ^[2] This guide does not determine how long a gap to leave with which medicine; the medicine’s package insert, the physician, and the pharmacist take priority.

Caffeine and pregnancy

Green tea leaf contains caffeine (2.9–4.2% of dry leaf); the amount in extract depends on the product. ^[1] The EFSA 2015 caffeine opinion reports that caffeine from all sources does not raise safety concerns up to 400 mg per day in nonpregnant adults, up to 200 mg per day in pregnant women, and up to a single dose and daily total of 200 mg in breastfeeding women. ^[7] Independently of caffeine, the EU regulation requires that green tea extracts not be consumed by pregnant and breastfeeding women and under age 18 (above). ^[8]

Who should take additional precautions with green tea extract?

• People with liver disorders: EFSA could not establish a safe EGCG dose for extracts; the Health Canada monograph cited by EFSA asks people with liver disorders to consult a health professional before use and to stop use if symptoms such as jaundice, abdominal pain, dark urine, sweating, nausea, unusual fatigue, or loss of appetite occur. ^[1]
• People using high doses (EGCG 800 mg/day and above) or using more than one green tea product together: transaminase elevation has been reported. ^{[1] [8]}
• People using it on an empty stomach: EGCG exposure increases. ^[1]
• Pregnant, breastfeeding, and under 18: no intervention study has examined these groups. ^[8]
• People using nadolol, atorvastatin, or raloxifene: interactions have been reported. ^{[5] [2]}
• People with iron deficiency: in women with low iron stores, pure EGCG reduced iron absorption in a dose-dependent manner ^[4]; the Health Canada monograph cited by EFSA also asks people with iron deficiency to consult a health professional before use. ^[1] For general information, see the iron guide.

This guide does not determine personal doses, products, or medicine gaps.

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