As little as 1 can
Depending upon your metabolism & sensitivity, even 1 can of red bull, which contains 76-80mg of caffeine
, can be too much for some individuals.
However, most adults can handle 200-300mg daily or the equialent of 3-4 cans. Once you clear 500-600mg daily, we tend to worry about side effects. Remember, your mileage may vary!