EGCG is a flavan-3-ol catechin polyphenol and the primary bioactive compound in green tea (Camellia sinensis), comprising up to 50–80% of the total catechin content in brewed green tea. It is isolated and concentrated in standardized green tea extract supplements, allowing doses far exceeding what is achievable through tea consumption alone. EGCG has been the subject of extensive human clinical research since the 1990s, making it one of the most studied plant polyphenols in nutrition science.

EGCG acts as a potent antioxidant, directly scavenging reactive oxygen species (ROS) and upregulating endogenous antioxidant enzymes such as superoxide dismutase and catalase. It modulates multiple intracellular signaling pathways including AMPK activation (promoting fat oxidation and glucose uptake), inhibition of NF-κB (reducing inflammatory cytokine production), and inhibition of DNMT1 (influencing gene expression through epigenetic mechanisms). EGCG also inhibits catechol-O-methyltransferase (COMT), an enzyme that degrades catecholamines like norepinephrine, thereby amplifying thermogenic signaling in adipose tissue.

Capsules of standardized green tea extract (typically 400–800 mg extract per capsule providing 200–600 mg EGCG) are the most clinically studied delivery format. Matcha powder provides the highest EGCG per serving among beverage sources. Decaffeinated green tea extract is available for those caffeine-sensitive. Powder forms allow flexible dosing but have a notably astringent taste.

• Weight Management / Metabolic Syndrome
• Cardiovascular Health
• Blood Sugar Regulation (Type 2 Diabetes Risk)
• Cognitive Function and Neuroprotection
• Inflammation
• Liver Health (Non-Alcoholic Fatty Liver Disease)

• Oxidative stress-related cellular damage (well-supported by RCT biomarker data showing reduction in 8-OHdG and F2-isoprostanes)
• Cardiovascular disease mortality (supported by large prospective cohort data, particularly Ohsaki Cohort Study, Kuriyama et al., 2006, JAMA)
• Progression from impaired fasting glucose to type 2 diabetes (supported by glucose and HbA1c reduction data across multiple RCTs)

• Matcha (powdered green tea) — Whole-leaf consumption delivers the highest EGCG per serving of any beverage — estimates range from 70–130 mg EGCG per gram of matcha, significantly higher than steeped green tea because the entire leaf is consumed.
• Gyokuro green tea (brewed) — Shade-grown Japanese green tea with among the highest catechin concentrations of any steeped tea; a single cup provides approximately 60–90 mg EGCG, higher than standard green tea due to reduced oxidation and growing conditions.
• Sencha green tea (brewed) — The most commonly consumed green tea globally; a standard 8 oz cup provides approximately 30–60 mg EGCG depending on steeping time, temperature, and leaf quality — represents the baseline dietary EGCG source for most populations.
• Oolong tea (partially oxidized) — Partial oxidation converts some catechins to theaflavins and thearubigins, but oolong retains meaningful EGCG levels (approximately 15–30 mg per cup), making it a secondary dietary source with its own complementary polyphenol profile.
• White tea (brewed) — Minimally processed from young Camellia sinensis buds, white tea retains a moderate catechin content including EGCG (approximately 15–25 mg per cup) and is notable for its very low caffeine content relative to its polyphenol load.

• Nausea and gastrointestinal upset (most common, particularly on an empty stomach; dose-dependent)
• Elevated liver enzymes / hepatotoxicity (rare but documented at high doses above 800 mg/day EGCG; reversible upon discontinuation in most cases)
• Insomnia and jitteriness (when non-decaffeinated green tea extract is used)
• Headache (reported in early dosing, likely caffeine-related in non-decaffeinated products)
• Reduced iron absorption (especially relevant with iron-deficient individuals; chelation effect)
• Mild hypotension or heart palpitations at very high doses
• Skin rash (rare hypersensitivity reactions)

• Recommended daily: 400–800 mg/day of EGCG (as standardized green tea extract providing at least 45% EGCG). Most positive RCTs used 400–600 mg/day. The European Food Safety Authority has flagged single doses above 800 mg/day as potentially hepatotoxic. Start at the lower end (400 mg/day) and assess tolerance.
• Best time of day: Morning or early afternoon. Caffeine-containing green tea extracts can disrupt sleep if taken in the evening. Some protocols split the dose (morning and midday) to maintain plasma catechin levels.
• With or without food: Take with food to significantly reduce risk of nausea and GI upset. Note that high-fat meals may modestly reduce EGCG absorption, so a light meal is preferred. Avoid taking within 1–2 hours of iron-rich foods or iron supplements to prevent chelation-mediated absorption interference.
• Time to effect: Acute antioxidant and thermogenic effects within 1–2 hours of dosing; sustained metabolic benefits (weight, lipids, glucose) require 8–12 weeks of consistent daily use.
• How long to take it: Most trials run 8–16 weeks continuously. Long-term daily use beyond 6 months at doses above 600 mg/day EGCG is not well-studied for safety. Periodic breaks (e.g., cycling 8–12 weeks on, 4 weeks off) are a reasonable precautionary approach for isolated high-dose EGCG supplementation. Dietary consumption of green tea carries no cycling requirement.