I don't have a dog in this fight, but the argument here seems persuasive.
You may notice that there is something striking about the way we define this “illness”—that is, by its symptoms, rather than its cause. If we were to define a heart attack by chest pain, then the appropriate cure would be painkillers, rather than the revival and repair of the heart. Other examples are easy to find: Nasal congestion can be a symptom of a cold, allergy, or many other conditions, but a runny nose is not a diagnosis. In the same way, the symptom complex associated with the ADHD diagnosis is related to more than twenty medical diagnoses, (from those as mild as poor eyesight, sleep deprivation, and even boredom in the classroom, to more severe conditions like depression and bipolar disorder), that, when treated effectively, can result in the disappearance of the attention-deficit and hyperactivity symptoms.