Well, everyone is different biologically and every drug affects everyone differently, I didn't mean that there's no biodiversity between people. What I meant was that these stimulants don't function differently based on whether you're "cognitively healthy." Methylphenidate doesn't do something different in a person with ADHD versus one without, because it doesn't interact with any mechanisms of the illness, and whether or not you have ADHD you're experiencing similar effects on the drug.
Contrast with, say, SSRIs, which might have some effect in a healthy person but you're looking at a different range of effects compared to someone taking it for depression/anxiety/OCD/whatever.
Contrast with, say, SSRIs, which might have some effect in a healthy person but you're looking at a different range of effects compared to someone taking it for depression/anxiety/OCD/whatever.