Two of our boys were diagnosed with adhd and one with mild autism also. They first went on Ritalin as the only alternative I had heard of was a cabbage diet.
Ritalin did help, they slept for 6hrs instead of 3, they were a lot better in school - but we had redress time when it wore off at home [ an hour where they were even more overstimulated than normal and worse than ever!].
We also gave the boys supplements of omega oils, magnesium,zinc,B-complex and found these all helped.
I looked into the leaky gut theory being as adhd is considered as being on the autistic spectrum.This is where the gut lining is damaged and so certain proteins 'escape' thru the wall and get into circulation around the body, stopping off at the brain where they act as 'excitotoxins' and do lots of damage.
From here we tried a gluten/dairy/additives/msg/aspartame free diet which was very stressful to do but did give us better results than the ritalin.I still carried on looking because this diet was like punishment for the boys and I found it very stressful.
From here we moved to natural digestive enzymes[Houston Neutraceuticals]which were nothing short of miraculous - these enzymes work on encouraging gut healing whilst taking care of the proteins which would cause the problems, so our boys were able to be on a normal diet [ altho there are some things we will never re-introduce now we know what they are etc.]-one of my sons now just appears an energetic boy, the other obviously has problems but his are so mild that they are only detectable by others because his movements and speech are a bit 'clumsy'and loud in appearance.
If you want to find out more about enzymes the yahoo group enzymesandautism is the place to go, and the sites below.

http://216.114.78.114/webcenter/sites/hni/
http://www.enzymestuff.com/