Been there, done that.
Speed is _bad_, I was there to see it destroy the Height in '67-68' OTOH it can be used
as a _TOOL_.
For myself, aside from the stress it puts on the bod', I become intolerable after about 50-60 days of use. I wouldn't mess with with caffeine or epeneferdrine though, prescription only, regardless of source is safest and has the least side effects.