My roommate was one of the largest Adderall prescribers in the United States. He has 20 cars, 3 homes and brags that he spends money "like a trillionaire". If you ask him where he lives, his response is, "what day?"
He is about 150 pounds overweight, dresses like a 90s rockstar and usually drives a Lamborghini Aventador. I don't trust he is impartial or an expert in his prescribing people what is effectively a daily routine of methamphetamine.
I know a few people who are prescribed Adderall who have attempted suicide. It's very easy to abuse amphetamines and abusing them makes one irrational. Meth has destroyed my hometown and as Dr. Carl Hart states, there is really no difference between Adderall and methamphetamine.
It is very dangerous to suggest that you can cure lack of focus by amphetamines, or that somehow this "ADHD" disease can only be cured by amphetamines.
If you're unsure if ADHD really exists, it may be useful to read the genetic studies that show ADHD correlation with specific SNPs, and decide for yourself [1]. Personally, I find the evidence satisfactory.
That said, I personally believe that ADHD type symptoms could be caused by several different disorders. ADHD is kind of like bipolar disorder - it covers a lot of areas and is sort of a fallback category when other diagnosis don't fit.
http://www.ncbi.nlm.nih.gov/pubmed/?term=ADHD,SNP