Green tea is made from the Camellia sinensis plant. It’s taken by mouth to reduce high levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia). It is also used to improve mental alertness and thinking, diabetes, low blood pressure, and many other conditions.

Polyphenols might be able to prevent inflammation and swelling, protect cartilage between the bones, and lessen joint degeneration.

Green tea contains 2% to 4% caffeine, which affects thinking and alertness, increases urine output, and may improve the function of brain messengers important in Parkinson's disease. Caffeine is thought to stimulate the nervous system, heart, and muscles by increasing the release of certain chemicals in the brain called "neurotransmitters."
Antioxidants and other substances in green tea might help protect the heart and blood vessels.