Green tea extract

Is green tea extract safe?

The drink, yes. The extract, much less so. A cup of green tea contains roughly 50 to 100 mg of EGCG, the main catechin. A green tea extract capsule can contain several hundred milligrams, and weight-loss products often recommend two or three a day. At those doses, a clear and dose-related liver signal appears, both in trials and in case reports.

That makes green tea extract one of the few supplements where harm has been shown at the doses people normally take. It scores 54, in the weak band, far below the drink it comes from.

What the trials show

The most useful evidence comes from the Minnesota Green Tea Trial, a year-long study in which 1,075 postmenopausal women took either green tea extract with 843 mg of EGCG a day or a placebo. Raised liver enzymes (ALT) were seen in 6.7% of those on the extract (36 women) against 0.7% on placebo (4 women), and 1.3% had elevations serious enough to be classed as serious adverse events. Enzymes returned to normal after stopping. A 2023 follow-up analysis found much larger ALT rises in women with one variant of the UGT1A4 gene, which helps clear EGCG.

In 2018 the European Food Safety Authority reviewed all the trial data and concluded that 800 mg or more of EGCG a day from supplements causes a statistically significant rise in liver enzymes. It could not identify a dose that was safe for everyone. For comparison, EFSA put typical EGCG intake from brewed green tea at 90 to 300 mg a day, while supplements on the market supplied 5 to 1,000 mg.

Severe liver injury

Beyond enzyme rises in trials, there are many case reports of acute hepatitis, some needing transplant and some fatal. In the US Drug-Induced Liver InjuryDrug-induced liver injuryLiver damage caused by a medicine, herbal product or supplement. It is usually rare and unpredictable, but it can be serious.More in the glossary Network, 40 of 1,414 formally assessed cases (3%) were attributed to green tea, often as part of multi-ingredient weight-loss or "fat burner" products. Most patients were jaundiced, 35% of cases were severe, and three people needed a liver transplant. Symptoms began a median of 72 days after starting the product.

Susceptibility seems partly genetic. DILIN researchers found HLA-B*35:01 in 72% of patients with green tea liver injury, against about 11% of the general population; the same variant is linked to turmeric injury. Taking the extract on an empty stomach also raises EGCG blood levels several-fold, and fasting or crash dieting appears in many case histories.

How regulators responded

The EU acted in December 2022. Commission Regulation 2022/2340 requires foods and supplements with green tea extract to contain less than 800 mg of EGCG per daily portion, to state the EGCG content, and to warn against exceeding 800 mg a day, against use by under-18s and pregnant or breastfeeding women, and against taking it on an empty stomach or with other green tea products. Green tea extracts also sit on the EU's scrutiny list (Annex III, Part C), because EFSA could not rule out harm below 800 mg. The Commission must decide within four years of the rule entering into force, so by December 2026, whether to ban these extracts in food or keep them restricted.

The European Medicines Agency's herbal committee reached a similar view for medicines in 2022. Its monograph covers only the leaf as a tea, with a maximum of about 317 mg EGCG a day, and it noted that the liver injuries reported in the EU were linked to high-dose dried extracts.

Health Canada and Australia's TGA also require warnings about rare liver injuryDrug-induced liver injuryLiver damage caused by a medicine, herbal product or supplement. It is usually rare and unpredictable, but it can be serious.More in the glossary: Canada's monograph for licensed green tea extract products tells users to stop and see a practitioner if their skin or eyes turn yellow or their urine darkens, and the TGA decided in December 2023 that oral medicines containing Camellia sinensis must say it may, in rare cases, harm the liver. In the US, no specific rule applies.

Interactions

The best-documented interaction is with nadolol, a beta-blocker. In a 2014 study in 10 healthy volunteers who drank 700 ml of green tea a day for two weeks, nadolol blood levels fell by about 85% and its effect on blood pressure was reduced, because tea catechins block a gut transporter (OATP1A2) that absorbs the drug. Green tea catechins may affect other drugs absorbed through the same transporters. Caffeine in many extracts adds to the effect of stimulants and can raise heart rate. Green tea contains some vitamin K, a theoretical issue for people on warfarin who change intake suddenly.

Who should avoid it

• Anyone with liver disease or who drinks heavily.
• Under-18s, and pregnant or breastfeeding women (EU label warning).
• People who have had liver injuryDrug-induced liver injuryLiver damage caused by a medicine, herbal product or supplement. It is usually rare and unpredictable, but it can be serious.More in the glossary from any herbal product, including kava or turmeric.
• People taking nadolol or other drugs where a pharmacist flags an interaction.

If you use it anyway

Keep total EGCG below 800 mg a day and preferably far lower; take it with food; avoid combining it with other green tea or "fat burner" products; and stop at once if you notice tiredness, nausea, dark urine or yellowing skin. If you want green tea's catechins, drinking the tea delivers them at doses with no known liver risk.

How we scored it

Organ toxicity (38) is the weakest factor: severe liver injuries, transplants and deaths. Dose safety (55) is low because liver enzyme rises occur at doses people actually take. Regulatory actions (45) reflect EU restrictions and warnings elsewhere. Interactions (72) are a relative strength.