As far as I have understood, the key reason why some people have ADHD is simply put that theyr brains do not process dopamine as effectively as they should. "Lighting up" dopamine receptors and dopamine production wih Ritalin or amfetamin like substances are meant to counter effect this.
However, if they key reason for ADHD is bad processing of dopamine, would not wrong issuance of these drugs possibly cause ADHD or ADHD like symptoms in the long run? I am not a doctor, but from what I have read, one of the side effects of excessive usage of any hormone in the long run is that it will numben the receptors for that hormone and inihibit its function. This in turn means worse processing of dopamine wich is the key reason to ADHD.
So, are we possibly producing ADHD in healthy children? One of the side effects of using amfetamine like substances is depression. The reason for that is (possibly among else) insensitive dopamine receptors as a result of excessive flooding of dopamine in the brain, wich again confirms my reason for this discussion.
As you might be suggesting to yourself, I am some what critical to this diagnosis of children. My impression is that this diagnosis is a easy "problem fixer" and that the usage of this practice is badly controlled as there is no way to surely lay down evidence of such a disease in a subject(even if the symptoms might fit).