I though discussing drugs is against the rules. But to be honest I confess to being an out of control chocolate addict myself...
But on a more serious note, theobromine is probably the most potent psychopharmacological agent in cacao. It's very closely related to caffeine in fact. Caffeine is the n-methyl homolog of theobromine. Another common stimulant in this class of compounds is theophiline, which is present in tea and is the n-methyl homolog of caffeine.
Makes you wonder if one couldn't tinker with this molecule a bit and optimize its beneficial effects
Also, fun fact: I read this study once where they gave caffeine naive volunteers caffeine and tested their cognitive performance which, as one would expect improved with the caffeine. As their tolerance built, their performance slowly began to decline again, but the interesting part is that it did't go back to baseline, suggesting that even long-term caffeine users still benefit from the drug!