What I'm pointing out is that all of these drug ideas are bound to be something that evolution has at some point tried out, and thrown away. And they are really unsophisticated ideas compared with those the brain has actually adopted.

Well there could be many reasons why evolution has" thrown them out". Maybe they are harmful in the long term, maybe their use consumes precious energy, or maybe they just aren't "good enough" for evolution to have kept them. That is, maybe they just don't give any signifigant evolutionary advantage.

Evolution doesn't create perfect beings, it creates beings which are good enough to survive.