If it's possible with this forum software, I think it would be good to allow for at least one 'custom' tag per post. Because no matter how many pre-defined tags you have, there will always be an obscure tag that is relevant to intelligence enhancement/general nootropics subject. A few tags I'll suggest: <Insert nootropic name and/or brand> {Aniracetam, Piracetam, <obscure drug name>, Concentration, Memory. I really think there are too many terms for them to be taken from a pre-defined list.
Verne, that is a great idea to allow one at least one custom tag. I don't know if the software allows it to work that way, or if it would let you have as many custom tags as you want while just providing standard tags as suggestions. The whole idea of standard tags is to make the tag system be more useful, since a vast profusion of tags, most of which are words in the title anyway, isn't really of much value, as no one would know what to search on, and few posts would have the same tag.
I think that general disease states, like depression, ADHD, OCD, etc would be good tags. I guess that would be in 'mental health', though Alzheimer's and Parkinson's would presumably be brain health. (To be honest, I think the difference between brain health and mental health is a little fuzzy.) You might be right about there being too many substance names. Maybe it would be better to tag substances with class names, like racetams, choline sources, SSRI's, MAOI's, etc.
I think 'brain health' is supposed to be a replacement for the word 'nootropic', although I think that isn't going to be obvious to most people. Maybe call it 'nootropics and brain health'?