Green tea is made from the Camellia sinensis plant. The dried leaves and leaf buds of Camellia sinensis are used to produce various types of teas. Green tea is prepared by steaming and pan-frying these leaves and then drying them. Other teas such as black tea and oolong tea involve processes in which the leaves are fermented (black tea) or partially fermented (oolong tea). People commonly drink green tea as a beverage.
As a prescription, green tea is used for genital warts. As a drink or supplement, it is sometimes used for high levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia) and high blood pressure, to prevent heart disease, and to prevent cancer of the lining of the uterus (endometrial cancer) and ovarian cancer. It is also used for many other conditions, but there is no good scientific evidence to support these other uses.
How does it work ?
The useful parts of green tea are the leaf bud, leaf, and stem. Green tea is not fermented and is produced by steaming fresh leaves at high temperatures. During this process, it is able to maintain important molecules called polyphenols, which seem to be responsible for many of the benefits of green tea.
Polyphenols might be able to prevent inflammation and swelling, protect cartilage between the bones, and lessen joint degeneration. They also seem to be able to fight human papilloma virus (HPV) infections and reduce the growth of abnormal cells in the cervix (cervical dysplasia). Research cannot yet explain how this works.
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.”
When taken by mouth: Drinking green tea is LIKELY SAFE for most healthy adults when consumed in moderate amounts (about 8 cups per day).
Green tea extract is POSSIBLY SAFE for most people when taken by mouth for up to 2 years or when used as a mouthwash, short-term. In some people, green tea extract can cause stomach upset and constipation. Green tea extracts have been reported to cause liver and kidney problems in rare cases.
Drinking green tea is POSSIBLY UNSAFE when consumed for a long time or in high doses (more than 8 cups per day). Drinking large amounts of green tea might cause side effects due to the caffeine content. These side effects can range from mild to serious and include headache, nervousness, sleep problems, vomiting, diarrhea, irritability, irregular heartbeat, tremor, heartburn, dizziness, ringing in the ears, convulsions, and confusion. Green tea also contains a chemical that has been linked with liver injury when used in high doses. In order to reduce the risk for liver injury, take green tea extract with food.
When applied to the skin: Green tea extract is LIKELY SAFE when a specific, FDA-approved ointment (Veregen, Bradley Pharmaceuticals) is applied to the skin, short-term. Green tea is POSSIBLY SAFE when other green tea products are applied to the skin, short-term.
The following doses have been studied in scientific research:
- For high levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia): Green tea or green tea extracts containing 150 to 2500 mg catechins, taken in single or 2 divided doses daily for up to 24 weeks, has been used.
- For high blood pressure: A green tea drink, made by boiling a 3 gram tea bag with 150 mL water, has been used three times daily about 2 hours after each meal for 4 weeks. Also, 379 mg of a specific product containing green tea extract (Olimp Labs, Debica, Poland), taken daily with the morning meal for 3 months, has been used.
APPLIED TO THE SKIN:
- For genital warts: A specific green tea extract ointment (Veregen, Bradley Pharmaceuticals; Polyphenon E ointment 15%, MediGene AG) applied three times daily to warts for up to 16 weeks, has been used. This product is FDA-approved for treating this condition.