I think it's more a matter of building up a tolerance. Everybody in my family drank coffee, all day long. We kids were served coffee routinely from about the time we were eight or nine for breakfast and again at dinner. Of course they didn't allow it at school so we didn't have any at lunch.   Now I CANNOT manage without coffee in the morning, and I have to have it by around 11:00 am at the latest or I get a splitting headache that lasts all day. I used to drink 10 cups a day but have cut back to six maximum. And now I mostly limit my coffee consumption to mornings. However, I am still able to drink a couple of cups of expresso before bedtime and then get a good night's sleep. I guess I should wean myself off all this caffeine but I really don't have any other vices and I do love my coffee! I despise decaf and won't touch it.