My office has a fancy espresso machine that I got a bit carried away with when we first got it. I don't really feel the caffeine effects when I drink it, I just really like the taste, so it was easy to drink a ton of it. The bad effect was if I went more than 24 hours without any (like on a weekend) and I got raging headaches. Last summer I was at 2x 3-shot espresso over ice, plus maybe a cup or two of drip later in the day. I just dropped last week from 2x double-shot espressos/day to a single triple shot. So far so good, no headaches or anything yet!