My point was as much that showing it is a blocker on the receptors is not the same as showing it just "builds up" in your system. It isn't so implausible that

My point was as much that showing it is a blocker on the receptors is not the same as showing it just "builds up" in your system. It isn't so implausible that I don't believe it, but a study would be good. Similarly, showing it moves to another part of your body does not imply that it is just "waiting its turn" for getting into the receptors later. Indeed, if they reach a steady state in the rest of your body, it seems to imply you are always binding less of it. The link you gave showing it is increased in plasma levels feels good. I would still question whether or not it only gets consumed in the receptors, versus changing where it is stored in the body. (That is, does your body "burn" the same amount of the stuff regardless of whether it is in the receptors or not?) That said, these questions are just asking how far we have come in understanding. And, really, my main point was to be fair to the question asked and see if there is evidence of the claim. And... quite frankly, there isn't. There were no studies linked showing that you will be tired later if you have coffee. None. To claim that what is there does that, is to hide behind sophistry of science to push claims that it isn't making.