This fact sheet provides basic information about green tea -- common names, uses, potential side effects, and resources for more information. All types of tea (green, black, and oolong) are produced from the Camellia sinensis plant using different methods. Fresh leaves from the Camellia sinensis plant are steamed to produce green tea.

How Green Tea is Used

Green tea is usually brewed and drunk as a beverage. Green tea extract can be taken in capsules and are sometimes used in skin products.

Laboratory studies suggest that green tea may help protect against or slow the growth of certain cancers, but studies in people have shown mixed results.

Some evidence suggests that the use of green tea preparations improves mental alertness, most likely because of its caffeine content. More data is being sought to determine how green tea aids in weight loss, lower blood cholesterol levels, or protect the skin from sun damage.

NCCAM is supporting studies to learn more about the components in green tea and their effects on conditions such as cancer, diabetes, and heart disease.

• Green tea is safe for most adults when used in moderate amounts.
• Green tea and green tea extracts contain caffeine. Caffeine can cause insomnia, anxiety, irritability, upset stomach, nausea, diarrhea, or frequent urination in some people. Caffeine can also raise blood pressure, and in very high doses, it can cause seizures, delirium, or irregular heart rhythms.
• Green tea contains small amounts of vitamin K, which can make anticoagulant drugs, such as warfarin, less effective.

Sources:
National Cancer Institute. Tea and Cancer Prevention. National Cancer Institute Web site.
Green tea. Natural Medicines Comprehensive Database Web site.
Green tea (Camellia sinensis). Natural Standard Database Web site.

See also:
Green Tea and Prostate Health
The Miracle of Green Tea

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