4-5 liters! Two liters of green tea typically contains over 400mg of caffeine which is the upper limit recommended for adults. This guy was consuming around 1g of caffeine a day.
EDIT: It's called theanine : https://fr.wikipedia.org/wiki/Th%C3%A9anine
I am quite sensitive to caffeine and yet I regularly drink green tea, typically around a liter and never get that weird anxiety I get from too much coffee. Maybe it's just that tea has less...
On the other hand green tea gives me nausea if I didn't eat anything in the morning.
daily coffee drinker