Article from the NYT
So caffeine can make you more alert or stay awake longer, but this doesn't translate into better performances. For some people, caffeine is counterproductive altogether.
I drink long coffee all day, made with a moka, and I really need at least two cups to start awakening. But to be honest, I keep drinking it throughout the day most for the company of the cup than for its effects. Also, I have tried several substitutes: tea, maca, herbs infusion but none where always pleasant as coffee.
How much caffeine do you drink? Has the amount increased over the time? Do you have a caffeine substitute?