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Limited evidenceWeight management

Green Tea Extract (EGCG)

Green tea extract is the single most common ingredient in "fat burner" formulas, and the Cochrane review found it produces essentially no weight loss — a pooled difference of 0.04 kg. Meanwhile, concentrated high-dose EGCG is one of the best-documented causes of supplement-induced liver injury.

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What the science says

  • Causes weight loss Limited evidence

    The Cochrane review of RCTs lasting at least 12 weeks found a pooled mean difference of -0.04 kg in six studies conducted outside Japan, with BMI -0.2 kg/m² and waist circumference -0.2 cm, none statistically significant. Japanese trials were too heterogeneous to pool and ranged from no effect to -3.5 kg, typically using tea beverages containing caffeine rather than isolated EGCG. As a standalone fat burner, green tea extract does not work.

  • Enhances fat loss when combined with exercise Limited evidence

    A 2024 meta-analysis of 10 randomized trials comparing exercise plus green tea against exercise plus placebo in overweight and obese adults found small effects on weight (SMD -0.30), BMI (SMD -0.33) and fat mass (SMD -0.29), with no heterogeneity, and no additional benefit on lipid profile. The authors' own conclusion was that green tea offers "quite minimal" additive benefit over exercise alone.

  • Is safe because tea is safe Limited evidence

    Concentrated extracts are not tea. A toxicology review documented numerous published cases of acute hepatitis associated with green tea extract, including cases requiring transplant, with liver injury judged probable or highly probable by causality assessment. European regulators concluded that supplemental doses of 800 mg/day or more of EGCG are associated with raised liver transaminases; brewed tea carries no comparable signal.

Dosage & safety

Studied doseWeight-loss trials used roughly 100–800 mg/day of EGCG (often 270–1200 mg total catechins) for 12 weeks, usually alongside 80–300 mg of caffeine — the caffeine likely accounts for most of the acute thermogenic effect. The regulatory liver-safety threshold flagged for supplements is 800 mg/day EGCG. Brewed green tea at 2–3 cups supplies roughly 90–300 mg EGCG with no established hepatotoxicity signal.
SafetyHepatotoxicity is the headline risk: acute hepatitis, and rarely acute liver failure requiring transplant, reported with concentrated extracts. Risk is highest with high-dose catechin-enriched extracts taken on an empty stomach; a genetic susceptibility marker (an HLA-B variant) has been identified in a subset of cases. Take with food, avoid doses at or above 800 mg/day EGCG, and stop immediately for jaundice, dark urine, right-upper-quadrant pain or unexplained fatigue. Several jurisdictions including Health Canada and EU member states require liver warnings on these products. Other issues: green tea polyphenols markedly reduce non-heme iron absorption; catechins reduce plasma levels of the beta-blocker nadolol; and most fat-burner formulas add substantial caffeine on top. Avoid in pregnancy at supplemental doses (high catechin intake may interfere with folate metabolism).

How to take it

TimingTiming does not matter for the measured outcomes, but avoid late doses if the product contains caffeine.
With food?Always with food — the liver injury cases cluster around high doses taken on an empty stomach.
Worth knowingBrewed green tea at two to three cups gives you 90-300 mg of EGCG with no established hepatotoxicity signal, which is the safer way to get it.

Interactions

With medications

  • nadolol and other beta-blockers

    Green tea ingestion greatly reduced plasma nadolol concentrations in healthy subjects, apparently by blocking intestinal uptake transport. separate by several hours, or avoid green tea products on nadolol

  • hepatotoxic medication (methotrexate, isoniazid, high-dose acetaminophen)

    Concentrated catechin extracts have caused acute hepatitis and rarely liver failure, so the risk is additive. avoid concentrated extracts, and stop for jaundice, dark urine or right-upper-quadrant pain

With other supplements

  • iron supplements

    Green tea polyphenols markedly reduce non-heme iron absorption. separate by at least 2 hours

  • caffeine and other stimulants

    Most fat-burner formulas already add 80-300 mg of caffeine on top of the extract. count the caffeine in the formula before adding more

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does green tea extract help you lose weight?

Green tea extract does not work as a standalone fat burner: the Cochrane review found a pooled difference of just 0.04 kg in trials outside Japan, not statistically significant (limited evidence). Combined with exercise, a 2024 meta-analysis found only a quite minimal additional benefit.

Is green tea extract bad for your liver?

Concentrated green tea extract is one of the best-documented causes of supplement-induced liver injury, with cases of acute hepatitis and rarely liver failure requiring transplant. European regulators link supplemental EGCG at 800 mg/day or more with raised liver enzymes, so stay below that, take it with food, and stop for jaundice, dark urine or right-upper-quadrant pain.

How much EGCG is safe per day?

Supplemental EGCG at 800 mg/day or more is the regulatory liver-safety threshold, and risk is highest with high-dose extracts taken on an empty stomach. Two to three cups of brewed green tea supply roughly 90-300 mg EGCG with no established liver-toxicity signal, which is the safer way to get it.

Does green tea extract interact with medications?

Green tea ingestion greatly reduced blood levels of the beta-blocker nadolol in healthy subjects, so separate the two by several hours or avoid green tea products on nadolol. Avoid concentrated green tea extract with hepatotoxic drugs such as methotrexate or isoniazid, and separate it from iron supplements by at least 2 hours.

Scientific references

Where to buy

NOW Foods, EGCg, Green Tea Extract, 400 mg, 180 Veg Capsules

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