Definately google Failsafe, i don't have ADHD but found positive changes in my mental health by removing the unsafe additives & preservatives from my diet and also Dairy.

And also don't think that because something is natural that it is okay. For instance i used to give my DS1 apricot yoghurt (a popular childrens brand), it is "naturally" coloured with 160b (annatto). He would become defiant and hyperactive after having one. It took me a bit of research and observation to link this but it is definately worth looking in to. I now buy a yoghurt completely free of colouring and no more hyper episodes. I think sensitivities run in the family, so it will be worth looking in to for once you have children also.