Safety & Interactions

EGCG is the main catechin in green tea, and although it is generally well tolerated, concentrated EGCG extracts raise real safety and interaction questions in oncology.

General tolerability

At commonly used doses, EGCG is usually well tolerated. The most common side effects are mild gastrointestinal symptoms such as nausea, abdominal discomfort, and loose stools.

Major safety issues

Liver risk at higher doses

Rare hepatotoxicity has been reported, especially with concentrated extracts at doses above roughly 800–1,000 mg/day and particularly when taken on an empty stomach.

Bleeding and platelet effects

EGCG has mild antiplatelet activity, so extra caution may be needed in people with thrombocytopenia, bleeding risk, or anticoagulant use.

Iron and folate considerations

• EGCG can reduce iron absorption

• It may interact with folate-related pathways through dihydrofolate reductase-related biology

• Iron and folate timing may need review in susceptible patients

Major drug interaction caution: bortezomib

This is the clearest high-priority interaction in the EGCG literature.

Avoid combining EGCG with bortezomib (Velcade). EGCG has been shown to antagonise bortezomib's proteasome-inhibition mechanism, which may reduce treatment efficacy.

Other interaction considerations

• CYP3A4-related drug metabolism

• P-glycoprotein modulation

• possible effects on taxanes, irinotecan, and other oncology drugs

• timing issues around chemotherapy and radiotherapy

How to interpret interaction evidence

Cell and laboratory findings can identify a possible interaction. They do not confirm the same effect occurs in people.

Read interaction claims alongside human pharmacokinetic and clinical evidence. See Drug Interaction Evidence and CYP Enzymes for the evidence hierarchy and practical questions to ask.

Practical takeaway

EGCG is not a high-toxicity compound in routine use, but high-dose extracts are not casual supplements. The main concerns are liver safety, drug interactions, and timing in active treatment.

Key References

Epigallocatechin-3-Gallate Therapeutic Potential in Cancer: Mechanism of Action and Clinical Implications
https://pmc.ncbi.nlm.nih.gov/articles/PMC10343677/

Anticancer Molecular Mechanisms of Epigallocatechin-3-Gallate (EGCG)
https://onlinelibrary.wiley.com/doi/full/10.1002/fsn3.70735

The roles of epigallocatechin gallate in the tumour microenvironment, metabolic reprogramming, and anti-cancer therapy
https://www.frontiersin.org/articles/10.3389/fimmu.2024.1331641/full