Known side effects of Green Tea include excess gas, upset stomach, nausea, heartburn, stomach ache, abdominal pain, dizziness, headache, and muscle pain. However, researchers in clinical trials consider these minor side effects. Doctors in one study on cancer patients taking Green Tea wrote, "We conclude that it is safe for healthy individuals to take Green Tea polyphenol products in amounts equivalent to the EGCG content in 8-16 cups of Green Tea once a day or in divided doses twice a day for 4 weeks." [30]

In summary, green tea is generally well-tolerated in humans. It is considered safe and effective, with relatively few side effects. However, patients should be cautious of drug interactions with certain medications.