I have read that ADHD is caused from food allergies . there was a very long article in 'alternative medicine' where the cure rate using food elimination was over 95%... the usual culprits, from what I've read - dairy, sugar, processed foods, etc...
i would get him tested... there are alternatives to using doctors to 'cure him'... NAET allergy elimination, and NMT, which I've gone through. NAET basically uses acupressure to resolve the allergy, and it bosts great success. NMT works much more quickly, and I can vouch that it did rid me of most of my food allergies . Initially I took NMT with a grain of salt because it is so way out there... it works energetically to rid the body of allergies. but i'm glad i stuck through it.
Neuromodular technique website (NMT) has info about where to find their practicioners.