Where did read that it hardened your arteries? How/why does that happen?
My understanding is that they are the same, caffine is an active ingrediant in the guarana plant. Similar to how ephedra is the active ingrediant in ma huang. I always get caffine pills because normally the few cheap guarana pills that I have seen don't have a % standarized for caffiene. This means that per pill it can be different, and normally if an herb doesn't have the % active ingrediant, it isn't a high %. With caffeine I know what I'm getting.
From wikipedia, "The Guaran