When green tea is not a healthy choice: green tea extract, other supplements and liver injury

Green tea is one of the world's most popular drinks, and brewed green tea is safe for the vast majority of people. Green tea extract is different. Sold as a natural health product for weight management and as a source of antioxidants, it concentrates the active ingredients of green tea into capsules, tablets, powders and liquids. In rare cases, it can cause serious liver injury, sometimes requiring a liver transplant. This article explains what is known about this risk, which other supplements can harm the liver or interact with medications, and how to protect yourself.

How is green tea extract different from green tea?

Both come from the leaves of the Camellia sinensis plant and contain antioxidants called catechins. The most important catechin is epigallocatechin gallate (EGCG). A typical daily intake of brewed green tea provides about 90 to 300 mg of EGCG. Supplements can provide up to 1,000 mg a day, often in a single dose.

The European Food Safety Authority concluded that brewed green tea is generally safe, but that taking 800 mg or more of EGCG a day as a supplement raises liver enzymes, a sign of liver stress. A review by the United States Pharmacopeia found that taking green tea extract on an empty stomach greatly increases the amount of EGCG that reaches the blood. Health Canada's label directions say to take these products with food.

What did Health Canada find?

There are more than 2,500 licensed natural health products in Canada that contain green tea extract. In 2017, Health Canada completed a safety review prompted by ongoing reports of serious liver injury worldwide, including a Canadian case. The review concluded that there may be a link between green tea extract and a rare and unpredictable risk of liver injury. Among the international cases it reviewed, one person developed chronic liver scarring and two needed a liver transplant. As a result, Health Canada:

• strengthened the label warning, which now advises people with a liver disorder to consult a healthcare practitioner before use;
• advised stopping use and seeing a healthcare practitioner if symptoms of liver trouble appear, such as yellowing of the skin or eyes (jaundice), stomach pain, dark urine, sweating, nausea, unusual tiredness or loss of appetite;
• limited these products to adults 18 years and older.

Unlike prescription medications, natural health products do not need large clinical trials to show that they are safe and effective before they are licensed, and the amount of EGCG can vary widely between products.

Why do only some people develop liver injury?

Most liver injury from green tea extract is idiosyncratic. It is not simply caused by taking too much, it is uncommon, and it is hard to predict. Two genetic findings help explain why some people are more vulnerable:

• An immune gene, HLA-B*35:01. In the US Drug-Induced Liver Injury Network, 72% of people with liver injury from green tea carried HLA-B*35:01, compared with about 12% of people whose liver injury was caused by medications, which is similar to the general population. This suggests that the injury is an immune reaction. The same gene was common in people with liver injury from supplements containing Garcinia cambogia, which is often combined with green tea in weight-loss products.
• A gene that helps clear EGCG, UGT1A4. In the Minnesota Green Tea Trial, postmenopausal women took a high dose of green tea extract (843 mg of EGCG a day) or a placebo for one year. Liver enzyme levels rose much more in women with one UGT1A4 genotype than in others.

Green tea extract also blocks several liver enzymes that break down medications, including CYP2B6, CYP2C8 and CYP3A, in laboratory studies. This can change the levels of some medications, which is one reason to be cautious when combining supplements and prescription drugs.

Which other supplements can harm the liver?

Liver injury caused by medications or herbal and dietary supplements is uncommon, occurring in an estimated 1 in 1,000 to 1 in 1 million people exposed, depending on the product. It is often unpredictable and may only be recognized after a product has been widely used. Together with antibiotics, cancer medications and antiseizure medications, herbal and dietary supplements cause more than half of these cases in Western countries. In the US, the share of cases caused by supplements rose from 7% in 2004 to 2005 to 20% in 2013 to 2014.

A 2026 review in JAMA lists the herbal and dietary supplements most often linked to this type of liver injury:

• green tea extract;
• multi-ingredient weight-loss supplements;
• turmeric with black pepper, taken as a supplement;
• black cohosh;
• Garcinia cambogia;
• ashwagandha;
• kava;
• kratom;
• khat.

These products are widely used. A US national survey found that about 15.6 million American adults had used at least one of six botanicals with known liver risks (turmeric, green tea, ashwagandha, Garcinia cambogia, red yeast rice and black cohosh) in the past 30 days, a number similar to those taking common prescription medications. Most used turmeric and green tea products to improve or maintain their health. Many supplements contain several ingredients, which makes it hard to know which one is responsible when a problem occurs.

About 75% of cases appear within 12 weeks of starting a new product. More than 80% of people recover fully when the product is stopped as soon as liver injury is suspected, but liver failure leading to death or a liver transplant occurs in up to 10% of cases. This is why stopping the product and seeing a doctor promptly matters.

How do St. John's wort and berberine interact with medications?

Some supplements are risky mainly because they change the levels of prescription medications:

• St. John's wort, used for low mood, strongly increases the activity of the liver enzyme CYP3A4 and the transporter P-glycoprotein. This speeds up the removal of many medications and can make them less effective, including cyclosporine and tacrolimus (taken after organ transplants), warfarin, digoxin, simvastatin, alprazolam, some HIV medications and oral contraceptives. In two heart transplant patients, this interaction caused acute rejection. The strength of the effect depends on the amount of hyperforin in the product.
• Berberine, popular for blood sugar, cholesterol and weight loss, does the opposite: it blocks several liver enzymes. In healthy volunteers, two weeks of berberine reduced the activity of CYP2D6, CYP2C9 and CYP3A4. Medications broken down by these enzymes include many antidepressants, opioids, blood pressure medications, blood thinners and statins, so their levels may rise.

Because these effects add to the effects of your genes and other medications, the safest approach is to avoid these supplements if you take prescription medications, unless your doctor or pharmacist has reviewed the combination.

Not all supplements are risky. Some can help improve mental health and can be safely combined with medications when chosen with your doctor or pharmacist. Read more about supplements for depression and anxiety: are they safe and effective?

How can a Pillcheck test help?

A Pillcheck test cannot predict who will develop liver injury from green tea extract or other supplements. Pillcheck does not report HLA genes yet, and the genetic risk for supplement-related liver injury is still being studied.

With Pillcheck, a pharmacist reviews your results together with all of your current medications and the supplements you take, accounts for drug-drug-gene interactions and prepares recommendations that you can share with your doctor. For example, if you are a CYP2D6 poor metabolizer and also take berberine, which blocks the same enzyme, the levels of some medications may rise even further. Still, the best advice is to avoid supplements that can harm the liver or interact with medications if you take prescription medications.

Pillcheck testing is performed in CAP- and COLA-accredited clinical genetic laboratories located in Canada. Pillcheck reports on 24 genes, increasing coverage with new guidelines and drug labels (see the genes tab), and covers 355 medications, which account for over 70% of dispensed prescriptions. The Pillcheck test panel ensures high accuracy for people of non-European and admixed ancestries. Your results last a lifetime, and report updates are free of charge.

Summary

• Brewed green tea is safe for most people, but green tea extract can rarely cause serious, unpredictable liver injury.
• Risk is higher with large doses of EGCG (800 mg a day or more) and when the extract is taken on an empty stomach.
• The immune gene HLA-B*35:01 is strongly linked to green tea liver injury.
• Weight-loss supplements, turmeric, black cohosh, Garcinia cambogia, ashwagandha, kava, kratom and khat have also been linked to liver injury. Supplements now cause about 1 in 5 cases of drug-induced liver injury in the US.
• St. John's wort and berberine change the levels of many medications. Avoid them if you take prescription medications, unless your doctor or pharmacist has reviewed the combination.

Frequently asked questions

Is drinking green tea safe?

Yes, for the vast majority of people. Brewed green tea contains much less EGCG than most green tea extract supplements. Rare cases of liver injury from brewed tea have been reported, so anyone who develops symptoms of liver trouble should see a doctor.

What are the signs of liver injury from a supplement?

Yellowing of the skin or eyes, dark urine, stomach pain, nausea, unusual tiredness and loss of appetite. Stop the supplement and contact a healthcare practitioner right away. Bring the product with you. Most people recover fully when the product is stopped early.

Does Pillcheck test for HLA-B*35:01?

No. Pillcheck does not report HLA genes yet. Most people who carry HLA-B*35:01 never develop liver injury, and liver injury can occur in people who do not carry it, so a test result alone would not show whether a supplement is safe for you.

Should I tell my doctor and pharmacist about my supplements?

Yes. Always tell them about all of the natural health products and supplements you take, including teas, herbal products and vitamins, especially before starting a new medication.

References

Chalasani N, Ghabril M, Vuppalanchi R. Idiosyncratic drug-induced liver injury. JAMA. Published online November 4, 2026.

Health Canada. Summary safety review: green tea extract-containing natural health products, assessing the potential risk of liver injury (hepatotoxicity). November 15, 2017.

EFSA Panel on Food Additives and Nutrient Sources added to Food, Younes M, Aggett P, et al. Scientific opinion on the safety of green tea catechins. EFSA J. 2018;16(4):e05239.

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.

Hoofnagle JH, Bonkovsky HL, Phillips EJ, et al. HLA-B*35:01 and green tea-induced liver injury. Hepatology. 2021;73(6):2484-2493.

Vuppalanchi R, Bonkovsky HL, Ahmad J, et al. Garcinia cambogia, either alone or in combination with green tea, causes moderate to severe liver injury. Clin Gastroenterol Hepatol. 2022;20(6):e1416-e1425.

Acosta L, Byham-Gray L, Kurzer M, Samavat H. Hepatotoxicity with high-dose green tea extract: effect of catechol-O-methyltransferase and uridine 5'-diphospho-glucuronosyltransferase 1A4 genotypes. J Diet Suppl. 2023;20(6):850-869.

Misaka S, Kawabe K, Onoue S, et al. Effects of green tea catechins on cytochrome P450 2B6, 2C8, 2C19, 2D6 and 3A activities in human liver and intestinal microsomes. Drug Metab Pharmacokinet. 2013;28(3):244-249.

Likhitsup A, Chen VL, Fontana RJ. Estimated exposure to 6 potentially hepatotoxic botanicals in US adults. JAMA Netw Open. 2024;7(8):e2425822.

Nicolussi S, Drewe J, Butterweck V, Meyer zu Schwabedissen HE. Clinical relevance of St. John's wort drug interactions revisited. Br J Pharmacol. 2020;177(6):1212-1226.

Guo Y, Chen Y, Tan ZR, Klaassen CD, Zhou HH. Repeated administration of berberine inhibits cytochromes P450 in humans. Eur J Clin Pharmacol. 2012;68(2):213-217.