Stimulant effects in cataclysm dda seem kind of underwhelming to me and some of the effects they have in real life don’t seem to be implemented at all. I know from a bit of digging around that they where nerfed becease they gave way to much of a buff to speed and intelligence spicificly which is why they where nerfed but the current effects that they have of only giving +2 speed and one perception before overdosing seem kind of underwhelming and not representative of how stimulants work. Stimulats are able to raise your athletic and cognative preformence in a number of way from increasing the strength and endurence of athletes, improving reaction time and coordination of martial artist and improving the focus, allertness and wakefullness that people have. The current effects simpely do not reflect this. A minor buff of 1+ to strength and dex (see improved reaction time, coordination and reflexes) and possibly a minor buff to stamina regen or stamina max allong with the current effects would better reflect the effects that stimulats have on athletic preformence. Another point is that stimulants directly increase ones focus and attention which is currently not implemented in the game eventhow this effect is so great that people actually use things like caffiene to improve study preformens and not just to counteract fatigue. This could be reflected by a direct bonus to focus depended on how much stimulant one has (lower levels of stimulants should give this focus bonus and it should possibly decrease at higher stimulant levels) applied on top of whatever focus you already have (something like +10 to 20 focus should do).
I do however think that keeping it so that stimulants don’t raise intelligence is a good idea both for gameplay purpeses (can’t make installing bionics to easy) and becease althow stimulants like caffiene have been shown to increase allertness and focus the effects on things related to intelligence like working memory or reasoning ability have been mixed.