I would not use more than 3-4 cups per day. Any more than that will be quite stressful for your body. If you really like coffee for its taste, try getting decaffeinated coffee - it would be a much healthier option. On the other hand, if you need coffee for the energy, you really need to limit its intake, because on the long run you will need to keep increasing the amount of coffee taken, which will lead to many stim related side effects, and crashes.