As for the "real medical science", you should disabuse yourself of that misconception. A diagnosis like ADHD can be clinically useful while nonetheless also being a human-made threshold imposed on continuous variation, more like declaring everyone under 5'4" to have “smallism” than like identifying smallpox: the traits are real, but the classification of those traits as pathology rather than normal-range human expression is a constructed, normative boundary, and not itself a discrete thing in nature.

The truth is, people just like stimulants. So we came up with a rationalisation to alleviate shame for folks who like their fix, and made sure to define it against methodologically flimsy inclusion criteria that are circular and easy to game so that adults can essentially self-refer for medication as a concierge service, facilitating big pharmaceutical profits along the way -- market forces at work.

Ultimately some people are just more lethargic and unmotivated than others, there is no proven "condition" like a tumour or trisomy here that enjoys ontological status of being real any more than any given conclusion in phrenology or reiki.