Yohimbine is an alpha-2 adrenergic antagonist that can raise adrenaline signaling, increasing energy and potentially liberating free fatty acids.

“so that is a alpha 2 adrenergic antagonist and when it comes to some of these like adrenergic type receptors it gets kind of confusing because some of them will have like even though it's an antagonist of the Alpha 2 receptors it will have stimulatory effects but contradictory to what you'd expect from a stimulant that's not vasoconstrictive the same way you might get from a amphetamine or like essentially any other stimulant that works well so this stuff raises adrenaline signaling very significantly and there was thought that it could liberate free fatty acids via the adrenic signaling that you could then you know like take advantage of during exercise”