I understand focus is related to dopamine, a neurochemical and it is know that nearly all neurochemicals can be depleted or their pathways become less effective

I understand focus is related to dopamine, a neurochemical and it is know that nearly all neurochemicals can be depleted or their pathways become less effective because of various run-time compensations that occur. Coffee effects me most for the first cup, most likely because I have stores of adrenaline and dopamine, after than first cup any cup after than decreases its effect on me. The first coffee probably is more noticable because of the difference between my no coffee state and my coffee state -- which is difference than a wearing off coffee state and a free cup coffee state. It is reasonable to be able to measure these effects. Not saying this effect is true, but neurochemical store depletion as well as real-time and long-term compensation are real.