On the other hand, you should consider what evolution can do. Evolution is not the world's best algorithm for inventing things. However, it is an excellent optimising algorithm. Balancing multiple considerations to decide the optimum amount of substance A in your body is the sort of problem that algorithm should do really well.

Essentially the only exception to this rule is when your cells are reacting to DNA/RNA that doesn't belong to you. If cold virus RNA is making your nose run, stop it by all means. But you should trust your own body on most other matters - adding extra chemicals is likely to turn out worse....

Note what's being optimised here - not intelligence, but biological fitness - how likely you are to reproduce successfully. You might improve intelligence somewhat, but there if there isn't a downside somewhere then Darwin was wrong.....