When are performance enhancing drugs ok, and why?

Usually, when people talk about performance enhancing drugs, they’re talking about anabolic steroids and sports. I don’t really play sports, so I’m not as concerned with those, but I think the same arguments apply.

I’m wondering more about performance enhancing drugs for cognition. We have drugs that can significantly help performance in academic and work settings, for instance, Adderall, Ritalin, and the non-stimulant Strattera. Normally, these are prescribed when people have a condition that causes them to have attention problems.

But people who don’t have problems can benefit from their use too. So, my question is: should they? Is it immoral, or unfair somehow for healthy people to use these? Are there circumstances in which it would be ok (e.g., fighter pilots are sometimes prescribed amphetamines) or is it never acceptable for people who don’t have some kind of condition? Suppose we someday live in a society where 99% of people are using cognitive enhancing drugs on a regular basis, putting you at a disadvantage if you don’t use them—would you, then? Why, why not?