Only for neurotypical people. For other populations the effect is real, I don’t know about clinical diagnostic tests but layman identifications commonly use “self-medicating with stimulants” as a red flag for suggesting someone seek a professional opinion.

So “can improve concentration”? Yes. Clinically proven. “Can improve [anyone’s] concentration”? Well you’re right that’s not true. But that’s relatively recent settled science, in part because there are plenty of anecdotes going back to Coca Cola being the “Thinking man’s drink” with coca leaves in it. Cocaine makes some people more focused. As does amphetamine, and methylphenidate.

But we’ve fucked the words “can” and “may” in legal terms. There is no accident that RFCs use MUST and WILL for mandatory behaviors, or that they’re in all caps.

That is assuming you would have a healthy baseline. Many people, for example those with undiagnosed/untreated ADHD, do not.

Drugs are complicated.

Just for the record, terming ADHD 'unhealthy' is a bit dubious.

It's maladaptive in modern society, for sure, but that's a combination of the trait and modern society. Not necessarily a reflection on the trait in itself.

ADHD is a disorder. Living with untreated ADHD doesn't just make society hard. It makes doing what I want to do hard, too.

Even in the perfect utopia, I would need medication to be healthy and enjoy life.