Green tea extracts have been used in traditional Chinese and Indian medicine for various uses. Tea extract is a herbal derivative of green tea leaves (Camellia sinensis). Antioxidant substances – mainly green tea catechins (GTC) – green tea and its derivatives are sometimes used as dietary supplements and in alternative medicine.
The cardinal antioxidative component in the green tea extract is green tea catechins (GTC) containing four major epicatechin derivatives, epicatechin (EC), epigallocatechin (EGC), epicatechinin gallate (ECG) and epigallocatechin gallate (EGCG). Other components include three types of flavonoids known as kaempferol, quercetin and myricetin. Significantly higher myriketin content is detected in tea and extracts, and this high concentration may have some effects with the bioactivity of myricetin. Kaffeine can be excluded in green tea extracts to avoid side effects; Decaffeinated green tea extract supplements are now available.