LSD (microdose 10ug-20ug daily)
Interesting. Did you find it to increase your concentration/focus? I recall that microdosing psychedelics can have that effect on some people. Of course everything is fucked because there is no way to be sure of the dose...and I personally have to steer clear of them for health reasons. But I wouldn't doubt that in the next fifty years this idea will be investigated much more thoroughly.
As for me:
caffeine
nicotine
medz