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Reviewed by the Scan Dose Research Team and Clinical Advisory Board

Green Tea Extract

MODERATE EVIDENCEBotanicalLast updated April 2026

SCAN DOSE SUMMARY

Green tea extract, primarily its catechin EGCG, has moderate evidence for modest fat oxidation enhancement and cardiovascular marker improvement. Our research also flags a critical safety concern: concentrated green tea extract supplements (particularly fasted or on empty stomach) have caused documented cases of acute liver failure — a risk NOT present with drinking green tea normally. The dose between "effective" and "hepatotoxic" is narrower than most consumers realize.

EVIDENCE GRADES

Fat oxidation / thermogenesisModerate — small consistent effects (PMID: 22626909)
B-
LDL cholesterol reductionModerate — meta-analysis confirms
B-
Blood pressure reductionModest effect
C+
Cancer preventionEpidemiological associations; RCT data mixed
C
Cognitive functionLimited clinical evidence
C

OPTIMAL DOSAGE

  • Fat oxidation: 250-500mg EGCG/day (often 400-800mg green tea extract standardized to 50% EGCG)
  • Cardiovascular: 500-1,000mg green tea extract/day
  • ALWAYS take with food — fasted consumption linked to hepatotoxicity
  • Do not exceed 800mg EGCG/day — European Food Safety Authority (EFSA) limit
  • Caffeine content: many extracts contain 30-50mg caffeine per capsule
Scan a supplement containing Green Tea Extract

DRUG INTERACTIONS

WarfarinModerate

Green tea contains vitamin K; may reduce warfarin effectiveness. Also EGCG alters CYP metabolism.

Nadolol (beta-blocker)Severe

EGCG reduces nadolol absorption by 85% via OATP transporter inhibition

Iron supplementsModerate

EGCG chelates non-heme iron; reduces absorption by 25-60%. Separate by 2+ hours.

Stimulant medicationsModerate

Green tea extract contains caffeine; additive stimulation

Folic acidModerate

EGCG may inhibit folate metabolism (dihydrofolate reductase inhibition)

CYP3A4 substratesMinor

EGCG inhibits CYP3A4 in vitro; clinical significance uncertain

Bortezomib (chemo)Severe

EGCG directly inactivates bortezomib — AVOID

SAFETY PROFILE

Drug Interactions

⚠️ Hepatotoxicity Warning

EFSA reviewed 21 cases of liver injury from green tea extract supplements (PMID: 29058885). Findings:

  • Risk increases when taken fasted (empty stomach)
  • Risk increases at doses >800mg EGCG/day
  • Mechanism: EGCG is dose-dependently hepatotoxic when rapidly absorbed without food
  • Several products withdrawn from market (Hydroxycut, Camellia sinensis extracts)
  • ALWAYS take with food. Never exceed 800mg EGCG/day.

Side Effects

  • Nausea, GI upset (most common)
  • Insomnia (caffeine content)
  • Liver injury (see above — dose and fasting dependent)
  • Iron deficiency with chronic high-dose use (iron chelation)

Pregnancy & Lactation

  • Green tea beverage: generally safe at 1-2 cups/day. Concentrated supplements: avoid (hepatotoxicity risk + folate interference + caffeine).

WADA Status

Not Prohibited

HOW SCAN DOSE SCORES THIS

Products >800mg EGCG per serving: automatic hepatotoxicity warning
"Take on empty stomach" instructions: flag as dangerous (EFSA finding)
Decaffeinated extracts score bonus for users sensitive to caffeine
Nadolol users: automatic SEVERE interaction alert (85% absorption reduction)
Iron supplementation users: 2-hour separation alert
Products in "fat burner" blends with undisclosed EGCG amounts: flag — can't verify safe dose

CLINICAL REFERENCES

1.

Hursel R et al. The effects of green tea on weight loss and weight maintenance: a meta-analysis.

PMID: 22626909

2.

EFSA Panel. Scientific opinion on the safety of green tea catechins.

PMID: 29058885

3.

Mazzanti G et al. Hepatotoxicity from green tea: a review of the literature.

PMID: 24268535

4.

Kim YC et al. Green tea catechin-induced hepatotoxicity.

PMID: 23447590

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Reviewed by the Scan Dose Research Team and Clinical Advisory Board | Last updated: April 2026

Not medical advice. Based on published clinical research and systematic reviews.

Safety

Green Tea Extract: Drug Interactions

Use with caution

Moderate interactions. Monitoring, timing separation, or dose adjustment may be required.

  • Nadolol (beta-blocker)

    Green tea catechins reduce nadolol absorption via OATP inhibition.

    RiskReduced blood pressure control.
    ActionSeparate by 4 or more hours, or avoid.

    Source: Clinical study

  • Warfarin

    Small vitamin K content plus catechin antiplatelet effect.

    RiskUnpredictable INR changes.
    ActionKeep intake consistent. Monitor INR.

    Source: Clinical consensus

  • Iron supplements

    Tannins in green tea chelate iron.

    RiskReduced iron absorption.
    ActionSeparate by 2 or more hours.

    Source: Clinical standard

  • Stimulant medications (Adderall, Ritalin)

    Caffeine in green tea is additive.

    RiskExcessive stimulation, anxiety, tachycardia.
    ActionLimit green tea on stimulant days.

    Source: Clinical consensus

  • MAOIs

    Caffeine plus tyramine interaction possible.

    RiskHypertensive crisis (rare).
    ActionAvoid high-caffeine green tea extracts on MAOIs.

    Source: Clinical pharmacology

Timing Separation Rules

  • Nadolol4 hours

Educational information only. This is not medical advice. These statements have not been evaluated by the FDA. Talk to your prescriber before starting, stopping, or combining any supplement with prescription medication.

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