How often can green tea be consumed?

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I wanted to get some additional help in losing some extra weight and so I've decided to try some green tea. But I've heard people say that it needs to be consumed at certain times and in certain quantities else it could lead to some inconvenience. I wanted to know from you guys your experiences with green tea. Is there any discomfort if had on an empty stomach, like acidity or something? Also, how many times can I have it? Should it before/after a meal? Before or after a workout? Also do you feel different after having green tea, maybe less sleepy, more active? Your responses will be greatly appreciated. Thanks! :)