Hello, Thanks a lot for your question.the phytochemicals Catechins and Caffeine that help you lose weight by Green Tea is considered a very popular weight loss beverage. It contains increasing your body’s energy expenditure (metabolism) and fat burning speed. However, excessive green tea consumption i.e. more than 5 medium cups per day is possibly unsafe and can cause side effects because of its high caffeine content. Possible side effects include: nervousness, anxiety, dizziness, irregular heartbeat and heart palpitations, stomach upset, diarrhea, and kidney and liver problems. What is more it can interfere with iron absorption and contribute towards developing iron deficiency anaemia. Green tea toxicity can occur at quite low doses so even though is a very health beverage it should not be consumed in excess. Aim for max 5 cups per day. Please let me know if you have any further questions. Thanks a lot