Herb ·Strong evidence ·Reviewed May 2026
Rich in EGCG catechins for antioxidant, metabolic, and cognitive benefits.
The bottom line
Evidence rating strong. Most-documented uses: antioxidant, fat metabolism, cognitive function. 19 sources indexed (2009–2025), with 15 interaction records on file.
Core mechanism
EGCG inhibits catechol-O-methyltransferase (COMT), extending catecholamine activity. Activates AMPK for fat oxidation and thermogenesis. Potent ROS scavenger.1,3
Take with food to reduce hepatotoxicity risk; avoid fasting use and avoid stacking multiple EGCG products3,4
Ranked by evidence and value.
Real-world pricing across three quality tiers. Assumes Decaffeinated EGCG Extract.
Assumes 250-500 mg/day. Vendor basis: NOW/iHerb, Vitacost, Life Extension, and Amazon marketplace; decaffeinated high-EGCG extracts cost more. Updated 2026-05-28.
How much you'd eat to match a supplemental dose.
Extracts can be much more concentrated than tea and may carry higher liver-risk concerns when taken fasting.
Dose: 250-500 mg daily standardized to EGCG
Timing: With food, never fasting
Clinical dose evidence: PMID 38031409. Avoid fasting use and keep total EGCG within safety guidance.
What to test, the optimal window inside the conventional range, and how long a response takes.
Green tea catechins (EGCG 200 to 400 mg per day) lower LDL by roughly 5 to 8 mg/dL in meta-analyses; modest effects on body weight and fasting glucose.15,1
High-dose green tea extract (above 800 mg EGCG per day) has been associated with idiosyncratic hepatotoxicity. Monitor ALT/AST and avoid on empty stomach.
Green tea extract is expected to modestly lower triglycerides, with effects that are typically small, dose-dependent, and clearest when baseline triglycerides are elevated.2,3
Triglycerides require a 9 to 12 hour fast and are strongly affected by recent alcohol and high-carbohydrate meals; standardize conditions between draws. High-dose green tea extract carries a rare risk of liver enzyme elevation, so consider checking ALT and AST. Retest after about 12 weeks.
Green tea extract may modestly lower fasting glucose, with effects that are typically small, dose-dependent, and clearest in people with elevated baseline glucose or insulin resistance rather than those already in optimal range.2,3
Fasting for 8 to 12 hours is required. Test at a consistent time of morning, as glucose varies with sleep, stress, and recent carbohydrate intake. High-dose green tea extract has rare reports of liver enzyme elevation, so consider checking liver function if used at high doses long term.
High-dose green tea extract, particularly catechin-rich EGCG formulations, can RAISE ALT in a subset of people because the liver is the primary site where these catechins are metabolized, and at high exposures they can stress or injure hepatocytes. ALT is tracked here as a safety signal to catch this rare but real hepatotoxicity early, not as a value the supplement is meant to lower. The evidence for this association is moderate, drawn largely from case reports and pharmacokinetic data rather than large controlled trials.3,7
Get a baseline ALT before starting a concentrated green tea extract, especially at higher EGCG doses, then recheck after several weeks if you continue use. Taking the extract with food rather than on an empty stomach may reduce catechin exposure and is the more cautious approach. ALT is not meaningfully affected by fasting, so the draw does not need to be fasted, though pairing it with a routine fasting panel is convenient. Stop the supplement and contact a clinician promptly if ALT rises noticeably above baseline or if you notice fatigue, nausea, dark urine, right upper quadrant pain, or yellowing of the skin or eyes. Because this involves potential liver injury, any persistent elevation or symptoms should be evaluated by a clinician, and people with existing liver conditions or who take other medications processed by the liver should consult a clinician before use.
Where this appears in the symptom-to-supplement map, ranked by relevance.
Catechins combined with caffeine can modestly increase thermogenesis and fat oxidation, producing small effects on energy expenditure.11,3
Effects are small and partly limited by caffeine tolerance, and high-dose concentrated extracts have rare liver toxicity reports.
EGCG from green tea showed reductions in fibroid volume and symptom burden in a small clinical trial, plausibly via antiproliferative and antioxidant effects.1,3
High-dose concentrated extracts carry rare liver risk, so take with food and discuss with your clinician; this supports, not replaces, care.
EGCG modestly increases energy expenditure and reduces visceral fat in meta-analyses.10,1
Avoid high doses on empty stomach due to hepatotoxicity risk.
Green tea polyphenols have anti-inflammatory and antioxidant effects that may calm redness, with the strongest signal from topical formulations and limited oral evidence.1,2
Use a decaffeinated extract if stimulants are personal flush triggers, and monitor liver tolerance at higher oral doses.
EGCG and other catechins may modestly improve glucose handling and insulin sensitivity through antioxidant and AMPK-related pathways.15,1
High-dose concentrated extracts carry a rare hepatotoxicity risk, so prefer modest standardized doses with food.
EGCG-rich green tea may produce small improvements in fasting glucose and insulin sensitivity, though trial results are mixed.1,12
Use modest doses with food; high-dose concentrated extracts carry a rare risk of liver injury.
Catechins and caffeine in green tea modestly increase satiety and energy expenditure, supporting appetite and weight goals.3,19
Effects are small; avoid high-dose concentrated extracts on an empty stomach due to rare liver concerns, and skip late in the day for sleep.
Evidence-based stacks that include it, with the exact dose and timing each one uses.
Modestly increases energy expenditure and supports visceral fat reduction; avoid high doses on empty stomach (hepatotoxicity risk).10
Green Tea Extract supplies catechins (notably EGCG) that may modestly support thermogenesis and fat oxidation, complementing appetite-focused efforts. Effects on body weight are small and inconsistent, and high-dose concentrated extracts should be taken with food because of a rare risk of liver injury.7,2
Catechins such as EGCG, together with any caffeine present, may give a small boost to fat oxidation and energy expenditure that could complement a fasting routine, though effects are modest and inconsistent. Take it with food rather than on an empty stomach, keep the dose modest, and avoid it in liver disease, since concentrated extracts have rarely been linked to liver injury, with risk rising toward and above 800 mg EGCG per day.15,1
COMT genotype modified the post-prandial insulin response to green tea extract in a randomized trial of overweight and obese post-menopausal women (PMID 27600055).
Recommendation: Treat metabolic effects from green tea extract as genotype-sensitive and monitor tolerability, especially when using concentrated extracts.
Green tea catechins, particularly EGCG, bind non-heme iron in the gut, reducing absorption by up to 60-70%. This is one of the most potent dietary inhibitors of iron absorption.
Recommendation: Separate iron supplements and green tea/green tea extract by at least 2 hours. Take iron in the morning on an empty stomach, green tea later in the day.
CLA and green tea extract are often combined for body composition support and may have complementary effects on fat oxidation and energy expenditure.
Recommendation: Acceptable to combine for weight management goals. Because green tea extract carries a dose-dependent hepatotoxicity risk, avoid high-dose extracts and prefer taking with food.
L-theanine smooths the caffeine stimulation from green tea extract, improving sustained attention while reducing jitteriness and the post-caffeine crash.
Recommendation: Pairing is favorable. A roughly 2:1 ratio of L-theanine to caffeine (for example 200mg L-theanine with 100mg caffeine equivalent) gives calm, focused alertness.
Both can lower blood glucose, so combining them may produce an additive hypoglycemic effect, especially during fasting or when also taking glucose-lowering medication.
Recommendation: Reasonable to combine for metabolic support, but monitor blood glucose and watch for hypoglycemia symptoms. Coordinate with a clinician if you take insulin or sulfonylureas.
Quercetin may raise plasma levels of green tea catechins by slowing their breakdown, and the two polyphenols provide additive antioxidant and anti-inflammatory activity.
Recommendation: Reasonable to take together for antioxidant support, with no special timing needed. Avoid stacking very high doses of multiple polyphenols if you have liver concerns.
Concentrated Green Tea Extract is one of the botanicals most consistently linked to liver injury in the US Drug-Induced Liver Injury Network, and Black Cohosh has also been reported (though with weaker, more disputed causality). Taking them together means simultaneously exposing the liver to two agents that have each been associated with hepatitis, cholestasis, or, rarely, acute liver failure. Reported latency for either ranges from a few weeks to several months. The combined risk is most relevant in people who also drink alcohol, take other hepatotoxic agents, fast before dosing, or have pre-existing liver disease.
Recommendation: Avoid routinely stacking standardized Black Cohosh with high-dose Green Tea Extract (especially EGCG concentrates taken on an empty stomach). If both are used, keep each within label doses, take Green Tea Extract with food, limit alcohol, and consider baseline plus periodic liver enzymes (ALT, AST, bilirubin) at roughly 4 to 8 weeks. Stop both immediately and seek care for dark urine, jaundice, right upper quadrant pain, nausea, or unexplained fatigue. Prefer brewed green tea over concentrated extract if hepatotoxic stacking is a concern.
Green tea contains vitamin K1 which can antagonize warfarin's anticoagulant effect. Concentrated green tea extract supplements provide substantially more vitamin K than brewed tea. High-dose consumption has been associated with decreased INR values in warfarin-treated patients.
Recommendation: If taking warfarin, avoid high-dose green tea extract supplements. Moderate consumption of brewed green tea (1-2 cups/day) is generally acceptable if kept consistent. Monitor INR when changing tea consumption habits.
Ciprofloxacin inhibits CYP1A2, the same enzyme that metabolizes caffeine present in green tea extract. This inhibition can roughly double caffeine half-life, leading to jitteriness, insomnia, palpitations, and increased blood pressure during the antibiotic course. People who normally tolerate green tea may notice exaggerated stimulant effects.
Recommendation: Reduce green tea extract intake while on ciprofloxacin, especially products with high caffeine content. Watch for jitteriness, insomnia, and palpitations. Return to your usual dose once the antibiotic is finished.
Green tea extract can contain concentrated EGCG and other catechins that inhibit catechol-O-methyltransferase in preclinical levodopa models. That could theoretically change levodopa methylation and exposure, especially with high-dose extracts rather than ordinary brewed tea. Human clinical interaction data are limited, so the main concern is new dyskinesia, nausea, insomnia, or motor fluctuation after starting a concentrated extract.
Recommendation: Avoid high-dose green tea extract unless your prescriber knows you take levodopa/carbidopa. If you use it, keep the dose consistent and watch for dyskinesia, nausea, palpitations, insomnia, or changes in wearing off. Ordinary dietary green tea is less concerning than concentrated EGCG products.
Green tea extract can sharply reduce fexofenadine absorption when taken together. In a randomized crossover study, an EGCG-rich green tea extract reduced fexofenadine AUC and peak concentration by about 70%. This may make fexofenadine less effective for allergic rhinitis or hives.
Recommendation: Take fexofenadine with water, not green tea extract or concentrated catechin products. Separate green tea extract from fexofenadine by at least 4 hours, and be consistent if you use both. If allergy control worsens after starting green tea extract, stop the extract or switch timing and reassess symptoms.
Green tea extract contains caffeine, which propranolol blunts the cardiovascular response to, and vice versa. High-dose green tea extract can also modestly raise blood pressure acutely from caffeine while EGCG produces opposite chronic vasodilatory effects, giving an unpredictable net effect when stacked with propranolol.
Recommendation: Limit high-dose green tea extract supplements while on propranolol; modest dietary green tea is usually fine. If you take a concentrated extract, monitor blood pressure and heart rate when starting.
Cimetidine inhibits CYP1A2, the main enzyme that clears caffeine. Caffeine-containing green tea extract taken with cimetidine can produce higher and longer-lasting plasma caffeine levels, raising the risk of jitteriness, insomnia, palpitations, and elevated blood pressure. A controlled study showed cimetidine reduced caffeine clearance significantly.
Recommendation: If you take cimetidine, prefer a decaffeinated green tea extract or limit total caffeine intake. Watch for signs of caffeine excess like racing heart or insomnia, especially in the first week of combining them.
Numbered references. Citations throughout the page link here.
Higher green tea consumption and EGCG intake were associated with reduced risk of several cancer types, with the strongest evidence for gastrointestinal and breast cancers.
Payne ER, Aceves-Martins M, Dubost J et al.. Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrition reviews. 2025
Daily consumption of EGCG 100-460 mg/day was effective for body fat and body weight reduction, especially in interventions of 12 weeks or more
EGCG supplementation was associated with reduced recurrence rates of colorectal adenomas and metachronous cancers following polypectomy or resection.
Wei F, Li D, Chen X et al.. Therapeutic effects of epigallocatechin-3-gallate for inflammatory bowel disease: A preclinical meta-analysis. Phytomedicine : international journal of phytotherapy and phytopharmacology. 2024
Wiese F, Kutschan S, Doerfler J et al.. Green tea and green tea extract in oncological treatment: A systematic review. International journal for vitamin and nutrition research. Internationale Zeitschrift fur Vitamin- und Ernahrungsforschung. Journal international de vitaminologie et de nutrition. 2023
Abunofal O, Mohan C. Salubrious Effects of Green Tea Catechins on Fatty Liver Disease: A Systematic Review. Medicines (Basel, Switzerland). 2022
Green tea catechins demonstrated protective effects against influenza infection and reduced the incidence of influenza-like illness in pooled analysis of clinical trials.
Tafazoli A, Tafazoli Moghadam E. Camellia Sinensis Mouthwashes in Oral Care: a Systematic Review. Journal of dentistry (Shiraz, Iran). 2020
EGCG intake moderately accelerates energy expenditure and reduces respiratory quotient, increasing fat oxidation rates by approximately 17%
EGCG administration was associated with significant increases in brain activity and increased self-rated calmness while reducing self-rated stress
Hepatotoxicity associated with EGCG intake 140-1000 mg/day; safe intake level of 338 mg EGCG/day as bolus dose or 704 mg/day in beverage form
Doses equal to or above 800 mg EGCG/day as a food supplement have been shown to induce significant increase of serum transaminases compared to control
Green tea influences anxiety reduction, cognition including memory and attention benefits, and brain function activation
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