A concentrated catechin extract of green tea leaf, standardised to epigallocatechin gallate. A single capsule can contain the catechin content of several cups of brewed tea, in a very different form.
Drinking green tea and swallowing a concentrated catechin capsule are not equivalent exposures, and the distinction is a safety issue rather than a technicality. Concentrated extracts have caused acute liver injury, sufficiently often that European authorities set a dose threshold for warnings and one botanical safety panel classified the extract as requiring a caution label. The weight-loss and metabolic effects that motivate the products are, meanwhile, small and inconsistent.
Commonly 45–98% EGCG or total catechins; caffeine content varies from negligible to substantial — a product without this marker may not resemble what was studied.
Also known as
EGCG, Green tea catechins, Camellia sinensis extract
Regulation: The European Food Safety Authority concluded that doses of 800 mg EGCG or more per day from supplements have been associated with liver injury, and several countries require warning labels. Green tea as a drink was not implicated in the same way.
What the research used
The amounts, forms and durations published trials of Green tea extract (EGCG) actually administered.
These are the amounts published trials administered — not a recommendation, and not a dose to copy. Trial participants were screened, supervised and given a characterised preparation. What is in a retail bottle is frequently not what was studied, and the amount that suits one person is not general advice.
Studied for Body weight and body composition
100–800 mg
Limited
Catechin extract expressed as EGCG, daily · 8–12 weeks
Weight changes in pooled trials average well under a kilogram and are not clinically meaningful. The upper end of this range is where liver injury reports cluster, so taking more is a worse trade rather than a better one.
Studied for Blood lipids
150–2500 mg
Limited
Green tea extract, divided doses · 3–24 weeks
The enormous range reflects trials that dosed whole extract versus purified EGCG. Reductions in LDL cholesterol are small and inconsistent between trials.
This is general information about food, not medical advice. It cannot diagnose, treat or replace guidance from a clinician who knows your history.
When it was taken
Each window says whether a trial compared it against an alternative, or whether it is convention and pharmacology. Most timing advice is the second kind.
Each timing below was actually compared against an alternative in a trial, which is unusual.
🍽️With food
Moderate
Catechin absorption is measurably higher when taken fasted, but the liver injury cases cluster in fasted high-dose use, and European guidance specifically advises taking extracts with food. This is one of the few timing questions in the category with pharmacokinetic data behind it.
Timing was tested. A trial compared this window against another and reported a difference.
The evidence in depth
Best supported: Limited
What each association actually rests on, and the papers behind it. A rating describes the state of the research, not how promising the supplement sounds. How we rate evidence.
Some meta-analyses report small reductions in total and LDL cholesterol. Trials vary widely in dose and preparation, and effects at the low end are marginal.
Limited evidence. Early human work, or mostly lab and animal research.
Pooled trials report average weight reductions of well under a kilogram against placebo, with results inconsistent between populations and larger in Japanese cohorts than Western ones. The effect is too small to be practically useful.
What may be going on: Catechins inhibit catechol-O-methyltransferase, prolonging noradrenaline signalling and slightly raising energy expenditure, an effect that overlaps with caffeine.
Limited evidence. Early human work, or mostly lab and animal research.
Meta-analysis · Journal of hypertension · 2015 · PMID 25479028
Deep research mode adds each paper’s own conclusion and stated limitations.
Things to know
Interactions, contraindications and dose limits, most serious first. Concentrated extracts interact with medication in ways the whole plant does not, so this section carries more weight here than it does on a food page.
Worth knowing
Liver injury from concentrated extracts
Acute hepatitis and liver failure have been reported with green tea extracts, most often at high doses and on an empty stomach, with a genetic susceptibility signal identified. Drinking brewed green tea has not shown the same pattern. Jaundice, dark urine or unexplained fatigue means stopping and getting liver tests.
Green tea markedly lowers blood levels of the beta-blocker nadolol in human studies, and affects other drug transporters. It has also been reported to reduce the effect of the cancer medicine bortezomib.
Interaction
Caffeine content and stimulants
Interacts withCaffeine, stimulant medication
Non-decaffeinated extracts carry meaningful caffeine, which adds to coffee, energy drinks and stimulant medication, and contributes to palpitations and insomnia.
Interaction
Iron absorption and warfarin
Interacts withWarfarin, iron supplements
Catechins bind non-heme iron and reduce its absorption, which matters in iron deficiency. Green tea also contains vitamin K, which can oppose warfarin.
Avoid
Pregnancy and existing liver disease
High-dose catechin extracts are avoided in pregnancy, partly over folate metabolism concerns, and should not be used by anyone with existing liver disease.
In the food catalogue
The whole-food form, where one exists. The evidence for a concentrated extract rarely transfers to the food, or the other way round — these are cross-links, not equivalents.