This has been said before, and was covered by Snopes 13 years ago:

Dr. Leon Eisenberg: ADHD Is a 'Fictitious Disease'? (5/16/2013)

Rumor: Dr. Leon Eisenberg, the 'father' of ADHD, said just before his death that ADHD 'is a prime example of a fictitious disease.'

And what did the source that we have come to know as a top outlet for phony deboonking have to say about the claim more than a decade ago?

Mostly True

The writeup is really pretty good at covering the relevant history, providing numerous specific points of documentation. The real point is this....

This type of information can be available, and in fact can be acknowledged by the mainstream. But the masses don't operate by what information is available and acknowledged by the mainstream. That's not how it works.

They believe what it is convenient for them to believe at any given time. As Yuri Bezmenov pointed out, they are beyond the usefulness of exposure to authentic information. It's like trying to soak water into concrete.

Everyone reading this needs to get beyond these false preconceptions. Well then, what is one to do in this situation? It isn't clear, is it?

Now you're at least pointed in the direction of the real problem.