It's not the absolute amount of adrenaline that you release in your brain and body that matters for enhancing memory; it's the amount of adrenaline that you release relative to the amount of adrenaline that was in your system just prior, particularly in the hour or two prior ... So, if you're going to chronically increase adrenaline, you're not going to learn as well. The real key is to have adrenaline modestly low, perhaps even just as much as you need in order to be able to focus on something, pay attention to it, and then spike it afterwards.