As I understand it, most drugs are still a pretty "blunt" from the standpoint of biochemistry. Too much of X causes some problem, so you make an antagonist for X. But X does a half dozen other things, and your X antagonist is going to affect them all. 99% of the time we call them "side effects", and they're bad. It's not that they have "no fucking idea" what they're doing; it's that sometimes there's no way to isolate the system they want to affect. The human body wasn't designed for external maintenance.