Caffeine turns me into my semi-dual (half throwaway thought, don't take it overly seriously).
I find that the stimulant effects of caffeine help me connect ideas and process information faster. I can usually keep one step ahead of people in conversation and figure out where their thoughts are going before they get there themselves.
Without any form of stimulant my mind is comparatively sluggish.
My incredibly half-baked thought (because my mind is crashing now) is: does Socionics measure anything that can be manipulated by manipulating neurochemistry, and if so, is it possible to thus induce a type-change via medication?