When too much is too much?

I thought this was rather interesting.

I like to drink coffee myself. I think the most I've ever had in ONE day was maybe 4 cups. But again, that was during the course of a day. I don't think caffeine affects me the same way as other people. I don't find that it "perks" me up. What I think it will do to me is interrupt my sleep pattern if I have some late enough in the day. Otherwise, if I'm feeling tired and sleepy, I will still feel tired and sleepy. I just like the taste of coffee.

Now double espressos on the other hand. That's got a bit more kick, I think.