Green tea extract is a herbal derivative from green tea leaves (Camellia sinensis), which contains antioxidant ingredients. Green tea and its derivatives are sometimes used as dietary supplements and in alternative medicine. Green tea extract exhibits stronger antioxidant protection for human body than vitamin C and vitamin E. Scavenging effect of lipid free-radicals (one antioxidant property) of polyphenols in green tea extracts can be clearly observed in experiments. Tea polyphenols are chemical compounds such as flavonoids and tannins found naturally in tea. Depending on how the tea is harvested, handled, processed, and brewed, the polyphenol level in the tea can vary. These chemical compounds are believed to be beneficial to human health, and they are the basis of many claims made about the health benefits of tea. As with many natural compounds which appear to be beneficial to human health, it is difficult to isolate and study tea polyphenols on their own, and some researchers have suggested that their actions in the body may actually be the result of several compounds working together.

Green tea contains a certain amount of caffeine. When it coexists with tea polyphenols, it can prevent caffeine from acting in the stomach, avoid stimulating the secretion of gastric acid, and make the disadvantages of caffeine not play in the body, but promote the functions of central nervous system, heart and liver.