I guess... You probably never do know when you have reached the limits of your intellectual reasoning ability. There are things you can do to improve your performance (practice, etc), but I guess you will never know whether you aren't improving because you have hit your limit or whether there is something else that you could do to improve it that you simply haven't tried yet.

All sorts of things affect our ability to reason. Emotional state. Tiredness. Etc.

'Intelligence' is a really general notion. Problem solving is one measure of intelligence, but it isn't the be all and end all. People aren't very good at multi-tasking. People can only keep 7 items (plus or minus two) on the 'workbench' of short term memory (thats why phone numbers are 7 digits long - so we can look them up and retain them in memory while dialing). Not that I can do that lol.

It can be hard to know whether feeling unfocused / foggy is impacting negatively on memory or whether it isn't - it just makes you worry that it might be impacting negatively. Retaining information on the workbench is a different ability to retaining information long term, however. And reasoning ability is different again. And all of those are distinguishable from intelligence (though sometimes are used as partial measures for it).

I worried that being on anti-p's would impact negatively on my reasoning ability, my attention to focus such that stuff was on the workbench, and the transfer from short term to long term memory. Attention can affect all that... Though attention isn't usually thought to be a measure of intelligence (or ADHD would count as a disorder of intelligence, presumably).

Hard to say...