Toxicity and Green Tea: What You Need to Know

Published on February 08, 2017 by Dr. NavNirat Nibber

Green tea supplements have come under fire recently following the release of a marketplace review.  The review focused on the adverse effects of green tea supplements on liver health and also highlighted the bigger issue of regulatory processes for natural health products. While the report brought up a number of valid concerns, it was somewhat reductionist. As proponents of natural health products we wanted to provide some insights into the complexities underlying this report and provide tips on what to look for in any supplement.

Green Tea – The Wonder Plant
Camellia sinensis, commonly known as green tea, has been long hailed as a “wonder plant”; provoking a boom in research in the last few decades with a focus on uncovering the benefits of consuming tea.

Green tea is composed of potent antioxidants that have been proven to have protective benefits against oxidative stress. The basic composition of green tea is caffeine, theanine (amino acid), GABA, vitamin C, and a group of polyphenolic compounds called catechins. Catechins are considered to be the most bioactive molecules found in the leaves of the plant. The most widely researched catechin includes epigallocatechin-gallate (EGCg) which has been the key molecule associated with health benefits.

Human clinical studies looking at the health benefits of green tea supplementation have been conducted and its effects on weight loss, normal cell growth, and dyslipidemia have been examined. Benefits were found when approximately 600-1300mg of catechins/day (3-10 cups of green tea) were consumed.

Supplements and Toxicity
It is true that calling something “natural” does not or should not imply “safe.” As some herbal supplements can be toxic when taken at certain dosages, there are a number of factors that may result in herbal supplements being toxic. This includes contaminants such as naturally occurring alkaloids or external microbes and pesticides, or the use of toxic solvents in the extraction process.

It is important to remember that plant material will vary greatly depending on the area in which they are grown (the soil and air quality), the part of the plant used, and the plant's own resistance to contaminants. Certain molecules of interest are often extracted from plant material. During this process many plants are being combined, dried, processed, and standardised for certain molecules in the extracts (e.g. epicatechin in green tea). This lengthy process emphasizes the need for batch-to-batch testing and the implementation of stringent quality assurance procedures. Raw material testing is imperative as is post-production testing (i.e. checking the final product for proper identification) and testing for the presence of microbes, heavy metals, and actual quantity.

Ideally, green tea extracts should be prepared using pure green tea leaves derived from areas where pesticides are prohibited and extracted using water or ethanol as a solvent. Every company should conduct some sort of third party testing for each and every herbal supplement they have on the market, as this limits exposure to risk factors that are definitively known to cause toxicity.

Adverse Effects of Green Tea Supplementation
Since the liver is the main detoxifying organ in the body, it is often the first victim of toxicity or injury. Liver damage can be measured by observing changes in enzymes such as ALT, AST, GGT, or by carrying out a biopsy of liver tissue. A recent report has criticized green tea supplements (particularly those developed for weight loss) for causing liver damage. In this report, 60 cases of “liver failure” were reported worldwide with “at least two deaths that were partially related." There are several issues with this report.

First, there seems to be significant variability amongst studies that have investigated adverse reaction relating to green tea extracts. For example, a different  review conducted in 2015 identified only 19 cases worldwide that resulted in liver damage. This variability may, in part, be due-to-the-fact that different inclusion criteria were used. When an adverse report is identified it is typically flagged and a “causality” scale is then used to identify if it is in fact related to the drug or herb in question. For example, was the herb used alone or with other supplements or pharmaceutical drugs? Or were there any pre-existing liver conditions, viral infections, or alcohol abuse? The 2015 review found that of the 19 cases, 58% were deemed “possibly” caused; while 42% were considered “probably” caused by the green tea extract. This method relies on accurate reporting of the adverse reaction such as whether an individual was tested for all viruses related to liver injury (HBV, HAV, HCV, CMV etc.)

Further, not all supplements are prepared to a high standard, which highlights the need for careful review of each supplement’s toxicity profile. Neither of these reports carefully analysed the extraction processes, the use of solvents, and potential other contaminants. It is therefore very premature and scientifically poor to infer that green tea supplements are indeed the cause of liver toxicity. Finally there are a plethora of other pharmaceutical drugs that are taken in conjunction with hepatotoxic drugs(acetaminophen, anastrozole, oral contraceptives, atorvastatin.) How can we be certain that these drugs are not linked with liver toxicity?  

It is also important to mention that other components of green tea leaves, such as L-Theanine (an amino acid) have not been linked with the adverse liver effects. Therefore, safety concerns associated with whole green tea extracts would not apply to individual isolates. It appears there are only very rare occurrences where the consumption of large green tea supplements caused significant liver damage. In these adverse reports, testing of the related products was not done retroactively and therefore they could not to rule out possible contamination.

Perspective on Drug and Herb Interactions:
Other investigations into adverse liver reactions and green tea supplements found that genetic variants in key liver enzymes made individuals particularly susceptible to high doses of catechins (1g/day.) So there is certainly cause for caution. ………But let's put this in perspective shall we?

Adverse drug reactions are among the five leading 

causes of death in the United States. Acetaminophen overuse is a well documented cause of intrinsic drug induced liver injury and 46% of individuals with acute liver failure in the United States had acetaminophen induced liver damage. Yet, this over the counter drug is widely used with little regard for the potential impact on the liver.

While this marketplace report does highlight the fact that we need to challenge the notion that all supplements are created equal and that are all safe no matter what the dosage, we still need to assess the risk based on epidemiologic evidence. Keep in mind that 60 possible cases (with 2 deaths) worldwide can reasonably be considered incredibly rare. So before we mount our pitchforks against all herbal supplements let's sit down, relax, and have a cup of green tea.


Hamilton LA, Collins-Yoder A, Collins RE. Drug-Induced Liver Injury. AACN Adv Crit Care. 2016 Oct;27(4):430-440.

Mazzanti, G., Di Sotto, A. & Vitalone. Hepatotoxicity of green tea: an update

  1. Arch Toxicol 2015 89: 1175. doi:10.1007/s00204-015-1521-x

Teschke, Rolf, and Axel Eickhoff. Herbal Hepatotoxicity in Traditional and Modern Medicine: Actual Key Issues and New Encouraging Steps. Frontiers in Pharmacology 6. 2015: 72. PMC. Web. 8 Feb. 2017.

Bonkovsky HL. Hepatotoxicity Associated with Supplements Containing Chinese Green Tea (Camellia sinensis). Ann Intern Med. 2006;144:68-71. doi: 10.7326/0003-4819-144-1-200601030-00020

Frenzel, C.; Teschke, R. Herbal Hepatotoxicity: Clinical Characteristics and Listing Compilation. Int. J. Mol. Sci. 2016, 17, 588.

García-Cortés M, Robles-Díaz M, Ortega-Alonso A, Medina-Caliz , Andrade RJ. Hepatotoxicity by Dietary Supplements: A Tabular Listing and Clinical Characteristics. Int J Mol Sci. 2016 Apr 9;17(4):537. doi: 10.3390/ijms17040537.