Green tea extract

What it is

Green tea extract concentrates the catechins from green tea leaves, particularly EGCG (epigallocatechin gallate). A cup of tea contains modest amounts; capsules can contain many cups worth in one go.

It is sold for fat loss, energy and antioxidant support, and appears in a lot of weight-loss blends.

How it works

Catechins and caffeine together may slightly raise energy expenditure and fat oxidation. EGCG is also a strong antioxidant in the lab. In practice, the effects in people are small.

What the evidence says

• Limited Weight loss
  Reviews show very small average losses, usually not enough to matter much.
• Moderate Short-term energy and alertness
  Mostly from caffeine and L-theanine in the tea, not the catechins.
• Limited Blood pressure and cholesterol
  Small improvements in some trials, mostly from drinking tea rather than capsules.
• Weak Cancer or disease prevention
  Observational and lab data only; no reliable proof from supplements.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• The European Food Safety Authority has advised that EGCG doses of 800 mg a day or more from supplements can raise liver enzyme levels in some people. Staying well below this is sensible; check current guidance.
• Drinking 3-4 cups of green tea a day is considered safe for most people and gives much less EGCG.
• Take with food; taking concentrated extract on an empty stomach appears to raise risk of side effects and liver stress.
• Avoid combining with other caffeine sources if sensitive.

Forms and what to look for

• Green tea itself is the lowest-risk way to get the compounds.
• Standardised extracts list the EGCG or catechin content; check mg per serving.
• Decaffeinated extracts exist, though they are still catechin-rich.
• Fat-burner blends often contain extra caffeine and other stimulants; avoid these if you are caffeine-sensitive.

What to expect, and when

• Any weight effect, if present, is slow and small over 8-12 weeks.
• Alertness effects from caffeine appear within an hour.
• Liver problems, if they occur, can appear within weeks to months.

Side effects

• Nausea, stomach pain and reflux, particularly on an empty stomach.
• Jitteriness, trouble sleeping and a fast heartbeat from caffeine.
• Headache.
• Liver enzyme rises, and rarely serious liver injury.
• Reduced iron absorption with long-term heavy use.

Interactions

• Reduces absorption of iron from food and supplements when taken together.
• May interact with warfarin (vitamin K content in tea; effect of extracts uncertain).
• May lower levels of some medicines such as nadolol (a beta blocker).
• Caffeine interacts with stimulants and some antidepressants and heart medicines.
• Combine with other liver-stressing substances with caution, including alcohol and high-dose turmeric.

Who should avoid it

• People with liver disease or a history of liver problems.
• Pregnancy and breastfeeding (caffeine and limited data).
• People with anxiety, heart rhythm problems or high blood pressure.
• Anyone on medicines affected by caffeine or catechins.
• Teenagers and anyone taking diet-style fat burners.

Risks and safety

• Concentrated extracts have been linked to cases of liver injury, particularly at high doses, on an empty stomach, or in fat-burner blends. Stop and seek help if you notice yellow skin or eyes, dark urine or severe tiredness.
• Fat-burner products sometimes contain undeclared or banned stimulants.
• Caffeine content is not always clear; some sports bodies set rules on it.

Buying well: quality and testing

• Prefer products stating EGCG per serving and total caffeine.
• Third-party testing (Informed Sport, NSF Certified for Sport) matters especially if you compete.
• Avoid proprietary fat-burner blends.
• Be wary of megadose labels.

Bottom line

If you like green tea, drink it. As a capsule it offers little benefit and a rare but real liver risk that grows with dose. If you do take an extract, take it with food, keep doses modest and stop it at the first sign of liver symptoms.