Special studies conducted about the human body revealed it will usually absorb up to about 300 milligrams of caffeine at a given time. About 4 normal cups. Additional amounts are just cast off, providing no further stimulation. Also, the human body dissipates 20% of the caffeine in the system each hour.
Personal note: To all my friends who marvel at my caffeine intake….see, after 4 cups it’s purely for the taste!