You say the same thing that doctors say about SSRIs: is certainly effective and fairly well understood in its clinical effects.

Yeah, of course we see the effects, but we still don't really know how exactly it works. For example, no one can tell for sure why Dextroamphetamine and levoamphetamine have different effects (the former is a brain stimulant, while the latter affects mostly the body). Adderall is mostly dextroamphetamine, by the way.