March 12, 2021: What are the Adverse Effects of Green Tea Extract?

Based on invitro studies, Green tea and specifically Green Tea Extract (GTE) have been heralded for antioxidant properties, benefits in weight loss, anticarcinogenic properties, reduction of insulin resistance and improving glycemic control.1-2 These properties have not been demonstrated in humans.  GTE is obtained from the Chinese tea tree, Camillia sinesis. Unlike black tea, it is unfermented and therefore unoxidized preserving multiple polyphenolic compounds. The benefits of GTE are largely attributed to polyphenols and specifically the biologic properties of the catechins (natural phenol found in plants), epigallocatechin galate (EGCG (also a catechin)) and epigallocatechin (EGC)most abundant catechin in tea) found in the extract.


GTE can be found in various dietary supplements and beverages and even in an FDA-approved topical treatment for anogenital warts.3 However, the catechin content is highly variable across different products.  The most commonly reported side effects are gastrointestinal-related including nausea, vomiting, diarrhea, abdominal pain and GI bloating, insomnia, headache, and palpitations have also been reported. Consumption of GTE on an empty stomach increases bioavailability and may be associated with increased adverse effects compared to the fed state. In some cases, the side effects appear to have a dose-dependent pattern.4-5


A few animal studies and case reports have suggested an association between GTE and hepatotoxicity especially with weight loss supplement (which led to the suspension of the market authorization for Exolise® in Europe)6-8   Since GTE is a dietary supplement, it does not require FDA approval so it is difficult to tell the concentration of each of the ingredients, especially catechins.



  1. Fukino Y, Ikeda A, Maruyama K et al. Randomized Controllled Trial for an Effect of Green Tea-Extract Supplementation on Glucose Abnormalities. Eur J Clin Nutr. 2008; 62(8): 953-960
  2. Yu J, Song P, Perry R et al. The Effectiveness of Green Tea or Green Tea Extract on Insulin Resistance and Glycemic Control in Type 2 Diabetes Mellitus: A Meta-Analysis. Diabetes Metab J. 2017; 41(4):251-262
  3. Meltzer SM, Monk BJ, Tewari KS. Green Tea Catechins for Treatment of External Genital Warts.  Am J Obstet Gynecol. 2009; 200(3): 233.e1-7. doi: 10.1016/j.ajog.2008.07.064
  4. 4.Jiang H, Webster D, Cao J, Shao A. The Safety of Green Tea and Green Tea Extract Consumption in Adults-Results of a Systematic Review. Regul Toxicol Pharmacol. 2018; 95:412-433
  5. 5. Sarma DN, Barrett ML, Chavez ML et al. Safety of Green Tea Extracts: A Systematic Review by the US Pharmacopeia. Drug Saf. 2008; 31(6):469-484
  6. Oketch-Rabah, HA, Roe AL, Rider CV et al. United States Pharmacopeia (USP) Comprehensive Review of the Hepatotoxicity of Green Tea Extracts. Toxicol Rep.2020; 7: 386-402
  7. Patel SS, Beer S, Kearney DL et al Green tea extract: A Potential Cause of Acute Liver Failure. World J Gastroenterol. 2013; 19(31): 5174-5177
  8. Younes M, Aggett P, Aguilar F et al. Scientific Opinion on the Safety of Green Tea Catechins. EFSA Journal. 2018; 16(4): e05239: doi:

Prepared by Roselyn Appenteng, MD, PGY-3 Pediatric House staff VUMC


EGCG is the catechin in GTE suspected of causing a hepatitis-like picture.  There are only invitro studies to support this association. Case reports of hepatic failure attributed to GTE are attributed because no other cause of liver failure can be identified. . The amount of catechins in GTE varies with each manufacturing process, so it is difficult to determine how much EGCG is in each GTE, let alone if there is an amount that will cause liver toxicity.  Hepatitis- like injury is more likely to occur when GTE is part of multi-ingredient nutritional supplement, making it difficult to determine what role GTE plays in liver injury. ds


Remember the doxy question? (it was the last question-sorry it’s been a while) Sean Donahue, MD PhD; Sam and Darthea Coleman Chair in Ophthalmology and Clinical Director of the Ophthalmology Patient Care Center, VUMC,  made some interesting comments that I wanted to share with you.  It’s always great to receive comments from experts who help further educate us. 


Another side effect of doxycycline that is rare, but I see about once a year is the development of Idiopathic Intracranial Hypertension (pseudotumor cerebri) in patients using doxy to treat acne. The most recent was an adolescent who was taking an oral vitamin A derivative for acne and presented to me with headaches and papilledema.  Workup for other causes of elevated CSF, including neuroimaging, was negative.  Vitamin A was discontinued, and she did well, until she returned with marked reoccurrence of symptoms and florid optic disc edema.  I asked how they had been managing the acne off the vitamin A and the mom said they had not done anything for about 6 months but  “started a new drug called doxycycline 4 weeks earlier!!” -Sean Donahue


I am interested in any questions you would like answered in the Question of the Week.  Please email me with any suggestion at


Donna Seger, MD

Executive Director

Tennessee Poison Center

Poison Help Hotline: 1-800-222-1222