Green tea is generally safe for most people when consumed in moderation. However, due to its caffeine content, consuming large amounts of green tea may cause side effects like headaches, insomnia, irritability, diarrhea, and heartburn in some individuals. Those with anxiety disorders or heart conditions should be cautious with high caffeine intake. Additionally, green tea contains tannins, which can reduce the absorption of iron and other minerals if consumed in excess or with meals.