Green tea extract appears in almost every “fat burner” on the shelf. The truthful version: there is a small real effect, it is nowhere near what the marketing implies, and high-dose extracts carry a genuine safety caveat.
What it actually does
Green tea contains catechins — mainly EGCG — plus caffeine. Together they can nudge energy expenditure and fat oxidation slightly upward. Studies that find an effect generally report a small one, often too modest to notice on the scale without other changes. The NCCIH keeps a balanced overview of green tea.
Brewed tea vs concentrated extract
Drinking green tea is pleasant, low-risk and mildly beneficial. Concentrated extracts are a different proposition: they deliver far more EGCG than anyone would get from drinking tea, and that is exactly where the safety reports cluster.
Green Tea Extract (e.g. NOW, Nature's Bounty)
- Effect on metabolism is real but modest
- Check the caffeine content if you are sensitive
- Avoid very high-dose EGCG products and take with food
Inexpensive
Check Price →Safety notes — read this part
There have been documented cases of liver injury associated with concentrated green tea extracts, particularly at high doses and when taken on an empty stomach. Drinking green tea has not shown this pattern. If you use an extract, choose a moderate dose, take it with food, and stop if you notice unusual fatigue, dark urine or yellowing skin. Anyone with liver problems should avoid these products.
For options with better evidence, see our metabolism-support guide and our explainer on fiber.