Categories Operation "Doppelganger" Caffeine: How much is too much? – Mayo Clinic Post author By Mike Nova Post date February 22, 2021 Up to 400 milligrams (mg) of caffeine a day seems safe for most adults. That’s about the amount of caffeine in four cups of brewed coffee, 10 cans of cola or two “energy shot” drinks. Keep in mind that the caffeine content in drinks varies widely.