I agree with Shazza. Our eldest son was diagnosed as having borderline ADHD, and he was offered Ritalin. I did a lot of research on this drug and even wrote to someone in the US who'd developed the compound. A doctor contacted me later, and said that the effects of Ritalin can be noticeable, but that it can irreversably alter the personality. On hearing that, I refused it, and decided to persevere in my own way, showing our son lots of attention and finding hobbies/sports to keep him interested.
it was found that in our case, there were no allergies or food intolerance, and that the ADHD was caused by a faulty gene. Hearing that was horrendous, but the consultant said he felt that our son'd outgrow the symptoms.
He did, and is an extremely bright, confident young man today, so best of luck.