This document outlines some potential minor side effects of green tea, including pregnancy risks from caffeine, catechins, and tannic acids; neural tube birth defects from large amounts of green tea; sleeplessness, irregular heartbeat, diarrhea, and other issues from more than 6 cups per day; and cautions for those with heart conditions, anxiety, kidney disease, or sensitive stomachs. However, it notes that green tea provides more benefits than harms unless consumed in extremely large quantities.