How much is over doing it? If you consume more than 250 milligrams (3 8-oz cups of coffee) in a couple of hours, your body pumps out stress hormones like epinephrine and cortisol. These hormones increase your heart rate, tense your muscles, and push your blood pressure higher. Yes, your brain will be more alert, but overdoing it will lead to a “crash” later in the day.
To best utilize caffeine, have small amounts throughout the day. Keep your daily total to 400 milligrams, or less, and don’t consume any caffeine after 3:00PM, or it will disrupt your sleep.