Green tea extract
CLimited evidenceWhat is Green tea extract?
Green tea extract is made by concentrating the polyphenols from the leaves of Camellia sinensis, the same plant that produces black and oolong tea. The compounds of interest are catechins, and the most studied is epigallocatechin gallate, usually abbreviated EGCG. A cup of brewed green tea contains roughly 50 to 100 mg of EGCG; supplement capsules commonly deliver several hundred milligrams, and some deliver far more. That concentration step is what separates a food from a supplement here, and it is also what changes the risk profile.
How it works
Catechins are proposed to influence weight through two routes: mild inhibition of the enzyme that breaks down noradrenaline, which modestly raises energy expenditure and fat oxidation, and some inhibition of digestive enzymes that reduces fat absorption. Both effects are real in laboratory conditions and both are small in people. Many products pair the extract with caffeine, and since green tea naturally contains caffeine unless it has been removed, part of what is attributed to catechins in some trials is likely the stimulant. The antioxidant activity that dominates the marketing is well demonstrated in a test tube and poorly translated into clinical outcomes.
What the research actually shows
Evidence strength varies by what is being claimed, so each use is graded separately against the published criteria rather than averaged into one reassuring letter.
For weight loss
CLimited evidenceThe NIH Office of Dietary Supplements concludes green tea might help with a small amount of weight loss. That phrasing is doing careful work: some trials find a difference, the difference is small, and results are inconsistent across studies and populations. Trials often combine catechins with caffeine, which makes attribution difficult. This is a marginal effect being sold as a primary one.
Sources: NIH Office of Dietary Supplements
For raising metabolic rate
CLimited evidenceShort-term studies do report modest increases in energy expenditure and fat oxidation after catechin doses, frequently alongside caffeine. The increases are small, appear to diminish with habitual caffeine use, and have not been shown to accumulate into meaningful weight change over months. A measurable change in a metabolic chamber is not the same as a change on the scale.
For cardiovascular or cholesterol benefit
CLimited evidenceObservational research associates green tea consumption with better cardiovascular markers, and some trials report small reductions in LDL cholesterol. The evidence is mostly drawn from drinking tea rather than taking concentrated extract, and the association in population studies cannot be transferred to a capsule without evidence that the capsule produces the same result.
For general antioxidant or anti-ageing benefit
DWeak evidenceCatechins demonstrate antioxidant activity in laboratory assays, and that finding underpins an enormous amount of marketing. Translating it into a clinical outcome in humans is a different matter, and the trials that would establish it have largely not been done. A mechanism in a test tube is a reason to investigate, not a reason to claim.
Effective dosage
Trials examining weight and metabolic outcomes have typically used 250 to 500 mg of catechins daily, often standardised to EGCG content and frequently with caffeine. There is no established effective dose, because there is no well-established effect to titrate against. Products vary enormously, from modest amounts matching a cup or two of tea to doses many times higher.
Where products diverge from the research. The concern here runs opposite to most ingredients: the problem is products that exceed the studied range rather than fall short of it. Because the marketing rewards a bigger number, some extracts deliver EGCG far above what trials used, which is precisely where the liver signal appears. It is also common to find green tea extract added to products sold as something else — a theanine capsule, a pre-workout, a multi-ingredient fat burner — so someone taking several products can accumulate a total they never intended.
Safety, side effects and interactions
This is the section that matters most. Concentrated green tea extract has been linked to liver injury in some people, and the NIH LiverTox database catalogues the case reports. The risk is associated with the concentrated extract rather than with drinking tea, appears more likely at higher doses and on an empty stomach, and can occur in people with no prior liver problem. Stop taking it and seek medical attention for yellowing of the skin or eyes, dark urine, pale stools, persistent nausea, unusual fatigue or pain in the upper right abdomen. Anyone with existing liver disease, or taking medication metabolised by the liver, should not take concentrated extract without medical advice. Unless a product states it is decaffeinated, it also contributes caffeine to your daily total, and green tea extract appears in many multi-ingredient formulas where it is easy to miss. It may also reduce absorption of iron and some medicines, including certain beta-blockers and statins.
None of this is medical advice. See the medical disclaimer for what that means before you act on anything here.
Products we have covered containing Green tea extract
Every label overview on this site whose Supplement Facts panel lists Green tea extract, with the amount each one discloses.
NOW L-Theanine 100 mg
A closer look at a relaxation-labelled formula containing both L-theanine and decaffeinated green tea.
Common questions
Is green tea extract the same as drinking green tea?
No, and the difference is the whole point. A cup of tea contains roughly 50 to 100 mg of EGCG; capsules commonly contain several hundred. The liver-injury reports are associated with the concentrated extract, not with the beverage, so the safety of tea drinking cannot be used to vouch for a supplement.
Can green tea extract damage your liver?
There are documented case reports of liver injury associated with concentrated green tea extract, catalogued in the NIH LiverTox database. It is uncommon, but it has occurred in people without prior liver disease. Higher doses and taking it on an empty stomach appear to increase the risk.
Does green tea extract burn fat?
The NIH position is that green tea might help with a small amount of weight loss. Short-term studies show modest increases in energy expenditure, often alongside caffeine, but these have not been shown to produce meaningful weight change over time. It is a marginal effect sold as a primary benefit.
Does green tea extract contain caffeine?
Usually yes, unless the label specifically says decaffeinated. That matters because it appears in many multi-ingredient products, so it can add to a daily caffeine total that is already higher than someone realises.
Who should avoid it?
Anyone with existing liver disease or taking medication metabolised by the liver should not take concentrated extract without medical advice. It is also worth avoiding on an empty stomach, and worth checking whether it is already present in other products you take.
References
Related ingredients
Last updated 21 September 2026 · Compiled by SNL Team