Brewed Tea vs Extract: The Key Distinction
There's an important difference between drinking green tea and taking a concentrated green tea extract supplement. Per NCCIH, 'no safety concerns have been reported for green tea consumed as a beverage by adults' — but the concentrated extracts are where caution is warranted [1].
The Liver Caution
NCCIH states: 'Although uncommon, liver injury has been reported in some people who used green tea products, primarily green tea extracts in tablet or capsule form' [1]. The concentrated dose of catechins (especially EGCG) in extract supplements is the suspected driver — far more than you'd get from a cup of tea.
NCCIH also notes that people carrying a particular immune-system gene variant appear more susceptible to this liver effect — a group estimated at roughly 5–15% of Americans [1]. There's no easy way to know in advance if you carry it.
Other Extract Effects
Beyond the liver, green tea extract supplements have been associated with nausea, constipation, abdominal discomfort, and increased blood pressure — concerns not reported for ordinary brewed tea [1].
What the Evidence Shows
NCCIH's overall read is cautious: 'although many studies have been done on green tea and its extracts, definite conclusions cannot yet be reached on whether green tea is helpful for most of the purposes for which it is used' [1]. So the benefit case is unsettled, while the extract carries a real (if uncommon) liver risk.
Practical Guidance
- If you enjoy green tea, the beverage has no reported safety concerns for adults.
- With extract supplements, avoid taking them on an empty stomach (which may worsen the liver risk), don't exceed label doses, and stop immediately if you notice fatigue, nausea, poor appetite, dark urine, or yellowing of the skin or eyes — then contact a clinician.
- Tell your clinician about green tea extract if you take other medications (see [Supplements and Medications](/learn/supplements-and-medications)).