I have a 10 year old kid diagnosed with severe ADHD-Inattentive type. He is on meds and behavioral therapy, and I must agree with most of the posts that meds is a must for these kids.
My very personal an unscientific explanation is that ADHD is not a disease in the traditional sense; instead, it is just a brain that does not fit in our current lifestyle. Would my kid have any problem living in a simpler society (hunter-gatherer group) ? Definitively not.
From time to time I tell my wife - and she gets very angry - that our kid has a MS-DOS brain, while we are all running Windows 10. The analogy is no exact, but it is just to emphasize that my kid belongs to another time. I only wish he can find his place in this world.