Side Effects and Cautions

• 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.
• Tell your health care providers about any herb or dietary supplement you are using, including green tea. This helps to ensure safe and coordinated care.