Tea leaves, flowers and a cup of green tea.

Green Tea: Drinks, Extracts, EGCG and Liver Safety

Posted on: Edited on: ~13 min read

What is green tea?

Green tea is made from Camellia sinensis leaves. It contains caffeine and a group of plant compounds called catechins. EGCG—epigallocatechin gallate—is one catechin often concentrated in supplements.

People drink green tea for its caffeine and take green tea extracts for weight loss or cholesterol.

How did tea become a daily drink?

Tea was first used as a medicine in China. By the Tang dynasty (618–907), people across social classes also drank it for pleasure and served it to guests. Tea houses made drinking it a social habit; poems, ceramics and Lu Yu’s eighth-century Classic of Tea helped make its preparation part of everyday culture. [1]

In Japan, monks brought tea from China in the eighth or ninth century. It was used in temples and at court; Eisai later introduced powdered-tea customs from Song China. Temple gardens spread production, and by the Muromachi period (1336–1573), tea sellers served ordinary people near shrines and at festivals. In Europe, growing imports made tea more accessible to households during the eighteenth century. Iruma City Museum[2] · Metropolitan Museum of Art[3]

Why do people take green tea?

Claimed benefit Dose / form studied Research verdict Evidence strength
Lower cholesterol Drinks and extracts with varying catechin amounts Pooled trials, mostly of capsules, found a small reduction in LDL cholesterol, the type often called “bad” cholesterol. The beverage-only estimate was uncertain. Limited
Lose weight Varied catechin/caffeine products Outside Japan, pooled trials found virtually no average difference in weight loss. The Japanese studies varied too much for a single estimate. Limited
Greater reductions in weight or cholesterol with a stronger extract Products vary in how much EGCG they deliver A higher EGCG amount has no established advantage for these outcomes. Insufficient

If you enjoy tea, a drink can fit an ordinary diet. Buying a concentrated extract for substantial weight loss is a different decision, with less reassuring safety information.

Are drinks and extracts equivalent?

A brewed drink and a capsule may both say “green tea,” but their composition and pattern of use can differ substantially. A supplement can deliver a concentrated amount quickly; drinking tea does not reliably reproduce that exposure.

EFSA's safety assessment[4] found traditional infusions generally reassuring while identifying liver concerns with supplements. Rare unpredictable reactions remain possible even with drinks. “Natural” and “decaffeinated” do not answer the EGCG safety question.

Preparation What goes into a serving What the amount tells you
Brewed green tea Hot water draws soluble compounds from the leaves. Early heating during production, often steaming or pan-firing, limits the oxidation that takes place when making black tea. The leaf weight, water volume and brewing time affect the drink. A cup count in an observational study gives an approximate drinking habit.
Matcha Finely ground leaves are whisked into water, so you drink the suspended leaf. Grams of powder identify the portion. Cultivar, harvest and processing can change its caffeine and catechin content.
Green tea extract Manufacturers concentrate selected constituents. Some extracts have most of the caffeine removed. An EGCG declaration gives the amount of that specific catechin. A label giving only the total extract weight leaves this unknown.

A study of 15 commercial teas measured total phenolics, a broad group of plant compounds, and EGCG, one specific catechin. Under that laboratory extraction method, the bagged and rolled teas had higher total phenolic concentrations than the matchas. Within the matchas, the less expensive culinary samples had higher total phenolics than ceremonial samples. For EGCG alone, the averages were about 51 mg per gram of culinary matcha and 57 mg per gram of ceremonial matcha, with no statistically clear difference across tea types. Neither the price nor a chemical assay tells you exactly how much EGCG you absorb from a bowl. [5]

A separate question for whole-leaf powder is what else the plant contains. An analysis of 12 matchas sold in Thailand detected several metals, including lead. At the assumed adult intake of 5 g per day, the authors judged the estimated exposures unlikely to pose a significant health risk. The estimate applies to those products and assumptions. [6]

What should you look for on the label?

Separate total extract, total catechins, EGCG and caffeine, all per full daily serving. They are not interchangeable amounts. “500 mg green tea extract” alone does not show how much EGCG or caffeine it contains.

The difference is visible on actual labels. NOW’s EGCg product[7] lists 400 mg extract with at least 200 mg EGCG and up to 4 mg naturally occurring caffeine per capsule. Nature’s Bounty’s green tea extract[8] lists 630 mg extract and 94.5 mg total polyphenols per two capsules, but does not state the EGCG amount. Its directions call for that serving twice daily; the printed serving amount is not the daily amount.

Combination products require another pass through the label. Herbalife’s UK Phyto Complete label[9] lists green tea alongside guarana, grape, grapefruit and black-carrot extracts, plus vitamins and chromium. It states 90 mg EGCG per two-capsule daily serving, but gives no caffeine amount for the combination. Guarana is another caffeine source[10], so count caffeine from the entire product and any other drinks or supplements; a green-tea study did not test this whole blend. The label also says not to take another green-tea product on the same day.

What are the drawbacks and interactions?

Potential drawback When / who it affects Research evidence Practical implication
Liver injury Particularly concentrated extracts; susceptibility varies Agency reviews identify trial signals and clinical reports. Ask a clinician or pharmacist before choosing a concentrated extract; this review cannot give a safe daily EGCG cutoff. Do not increase the dose on your own. Stop and seek care for yellow eyes/skin, dark urine or severe unusual fatigue.
Stomach symptoms or increased blood pressure Some extract users NCCIH reports these effects. Reconsider the product if symptoms occur.
Caffeine-related sleep or stimulant effects Sensitive users or stacked caffeine products Caffeine is a separate active exposure. Count it alongside coffee, tea and other supplements.
Medicine interactions Including nadolol, atorvastatin or raloxifene Human studies show reduced blood levels of some medicines, including nadolol; the clinical importance depends on the medicine and preparation. Have a pharmacist review the exact product and medicines.

Which medicines have actually been studied?

The studies below measured how much medicine reached the blood after a dose. Researchers compared drug levels with and without a particular tea or extract. Some studies tested a single serving of tea and others measured the drug after repeated tea intake. Changes can run in either direction depending on the drug.

Medicine Tea preparation and comparison Result in the volunteers
Nadolol After two weeks drinking 700 mL of tea daily, volunteers took a single nadolol dose with tea. A separate study tested 150 mL taken with the drug or one hour beforehand. Nadolol exposure was about 85% lower with tea than with water in the first experiment. Even with the one-hour gap in the second, it was about 46% lower. Repeated tea[11] · Timing study[12]
Lisinopril A 10 mg tablet with water or a green-tea extract drink supplying about 300 mg EGCG. Total exposure fell by about two-thirds with the extract. The time to peak concentration was similar. [13]
Fexofenadine and pseudoephedrine Ten healthy volunteers took both medicines with water or extract containing about 300 mg EGCG. Fexofenadine exposure fell by 70%. Pseudoephedrine exposure showed no clear change in the same people. [14]
Digoxin Fifteen volunteers completed a study taking digoxin one hour after a green-tea catechin preparation, both on first use and after repeated dosing. Exposure over the eight-hour measurement period was about 31% lower on the first occasion and 33% lower after repeated use. [15]
Atorvastatin or rosuvastatin Separate studies tested single doses of the two statins. The atorvastatin experiment used 300 or 600 mg of dry extract. The rosuvastatin experiment used an extract labeled as supplying 800 mg EGCG daily for two weeks. Both studies found lower blood exposure. Neither measured long-term cholesterol control, and their extract amounts describe different materials. Atorvastatin[16] · Rosuvastatin[17]
Sildenafil Ten men took sildenafil and the test medicine midazolam with water or a drink made from 2 g of tea. Sildenafil exposure was about 50% higher with tea in this small study. [18]

Green tea has also reduced exposure to raloxifene in a human study. For anyone taking one of these medicines, the relevant question for a pharmacist is how the exact drug, preparation and timing fit together. The nadolol and digoxin results show why separating everything from tea by one hour would be unreliable. [19]

Tea taken with an iron-rich meal

A Moroccan study gave women a wheat-flour meal fortified with a known amount of iron, once with water and once with 300 mL of green tea. Among women with iron-deficiency anemia, median absorption of the tagged iron fell from 36.7% with water to 4.1% with tea. It also fell among women without anemia. If you are treating iron deficiency, ask how to schedule tea around your iron supplement and iron-rich meals. [20]

What do human studies show?

Drinking habits and heart health: trials found small changes in cholesterol and pressure

The Ohsaki study followed 40,530 Japanese adults who reported how often they drank green tea. More frequent drinkers had lower rates of death from cardiovascular disease during up to seven years of follow-up. The association was strongest for deaths from stroke. People chose their own diets, so differences in their health, food or other habits could account for some of the association. [21]

Blood-pressure trials tested a different question. A pooled analysis of green-tea interventions found that systolic and diastolic pressure were each about 1.2 mm Hg lower on average than in the control groups. These small changes in measured pressure do not explain how much of the association in Ohsaki was due to tea. [22]

Trials that assigned people to green tea or a comparison provide a more direct test of cholesterol. A pooled analysis found LDL cholesterol about 4.6 mg/dL lower on average across drinks and capsules, with no clear differences in HDL cholesterol or triglycerides. Most trials of LDL used capsules. In the beverage-only subgroup, the estimated reduction was smaller and its uncertainty included no difference. [23]

Nature’s Bounty describes its extract[8] as offering “antioxidant support” and says green tea has traditionally been used for heart health. Those are manufacturer claims, not the endpoints tested in the lipid trials. The pooled LDL change is small; the trials do not establish that this particular product prevents heart attacks or strokes.

One study found higher energy use for a day. Longer trials found little or uncertain weight loss.

In a chamber study of ten men, a catechin-and-caffeine extract increased energy expenditure over a single day by about 4% compared with placebo. The comparison using the same amount of caffeine alone did not show that effect. This short experiment helps explain the interest in green tea for weight loss, but measured neither a lasting change in appetite nor lost body fat. [24]

Longer trials give a different perspective. A Cochrane review found virtually no average difference in weight loss among the 532 participants in studies pooled outside Japan. The Japanese studies varied too much for a single pooled result. In a year-long study of a decaffeinated extract, body mass index and fat mass did not clearly improve compared with placebo. In a separate trial in adults with type 2 diabetes, HbA1c, a measure of average blood sugar over roughly three months, fell from its starting level in the extract group, but no measured outcome clearly differed between groups. Ghrelin, a hormone involved in appetite, rose from its starting level in both groups. Cochrane review[25] · Body composition trial[26] · Diabetes trial[27]

A combination product may borrow green tea’s weight-loss reputation while adding other ingredients. The Phyto Complete label[9] calls its green-tea-and-guarana blend “scientifically studied,” but its energy-metabolism language is specifically attached to vitamins B3 and C, and its blood-glucose language to chromium. The green-tea weight trials above cannot establish a weight-loss effect for that blend.

Attention today and cognition over a year

Caffeine and L-theanine, an amino acid in tea leaves, have been tested together. In a 27-person experiment, 50 mg caffeine plus 100 mg L-theanine improved performance on selected attention tasks compared with placebo. Caffeine alone improved alertness and performance on one task as well. Another crossover study used a different ratio, 75 mg caffeine and 50 mg L-theanine, and found no additional cognitive advantage with the combination. The result depends on the task, dose and timing. Attention experiment[28] · Four-condition crossover study[29]

A year-long trial assigned 99 older adults with memory concerns or mild cognitive impairment to 2 g of matcha powder a day or placebo. Its two main measures, a cognitive screening score and a measure of everyday activities, showed no clear advantage with matcha. The authors reported a favorable secondary result on a test of recognizing facial emotions. One statistical test favored matcha on emotion recognition, but the reported range of plausible effects also included no advantage. Sleep scores also showed no clear advantage. [30]

Is there a safe daily EGCG dose for extracts?

The available evidence gives no reliable daily EGCG cutoff below which a concentrated extract is safe for everyone. In a 30-person single-dose study, the average peak blood level of free EGCG was more than three times higher after an overnight fast than after a light breakfast. [31]

In the year-long Minnesota trial, women took capsules with breakfast and dinner. At a daily dose of 843 mg EGCG, 44 of 513 extract recipients reached the trial’s elevated ALT threshold, compared with 9 of 508 on placebo. ALT is a blood marker of liver injury. Taking an extract with food cannot remove that risk. [32]

EFSA found increased liver enzymes in trials using 800 mg EGCG a day or more as supplements. That is a warning signal, not a recommended amount or a safe ceiling. The UK Committee on Toxicity[33] also discusses injury associated with a product providing 375 mg EGCG daily. A smaller label number cannot guarantee safety.

The bottom line

Brewed tea and matcha can be chosen for their taste and caffeine. Trials of mostly extracts found a small average LDL reduction. A year on the tested concentrated extract produced little change in body fat, and a separate year-long trial of whole-leaf matcha found no clear benefit on its main cognitive or daily-living tests.

If you are considering capsules, the extract weight, daily EGCG, caffeine and your medicines matter more than the marketing term “antioxidant.”

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References

  1. Smithsonian National Museum of Asian Art ↩
  2. Iruma City Museum ↩
  3. Metropolitan Museum of Art ↩
  4. EFSA scientific safety opinion ↩
  5. Commercial tea comparison ↩
  6. Thai product study ↩
  7. NOW’s EGCg product ↩
  8. Nature’s Bounty’s green tea extract ↩
  9. Herbalife’s UK Phyto Complete label ↩
  10. Guarana is another caffeine source ↩
  11. Repeated tea ↩
  12. Timing study ↩
  13. Lisinopril study ↩
  14. Combination medicine study ↩
  15. Digoxin study ↩
  16. Atorvastatin ↩
  17. Rosuvastatin ↩
  18. Sildenafil study ↩
  19. Raloxifene study ↩
  20. Stable-isotope meal study ↩
  21. Ohsaki cohort ↩
  22. Blood-pressure review ↩
  23. Lipid review ↩
  24. Energy-expenditure study ↩
  25. Cochrane review ↩
  26. Body composition trial ↩
  27. Diabetes trial ↩
  28. Attention experiment ↩
  29. Four-condition crossover study ↩
  30. Matcha trial ↩
  31. Fed and fasted extract study ↩
  32. Minnesota liver safety study ↩
  33. UK COT 2024 safety summary ↩
  34. NIH NCCIH: green tea