Although I agree that is possible, the extreme variations in dosage between individuals could be explained simply by variations in the liver enzymes that metabolize stimulants, and don't necessarily point to different underlying causes of ADHD itself. However- I think the fact that entirely different classes of drugs, including non-stimulant medications, seem to work better for different people with ADHD does point to what you are saying.
In my case I can't tolerate even 2.5mg of adderall, and I also have hypersensitivity to several other non-psychiatric medications that happen to be metabolized by the same enzymes as adderall/amphetamine, so I am nearly certain it is a liver enzyme issue. I do tolerate a reasonably high dose of methylphenidate (ritalin) without any euphoria or insomnia.
In my case I can't tolerate even 2.5mg of adderall, and I also have hypersensitivity to several other non-psychiatric medications that happen to be metabolized by the same enzymes as adderall/amphetamine, so I am nearly certain it is a liver enzyme issue. I do tolerate a reasonably high dose of methylphenidate (ritalin) without any euphoria or insomnia.