Both my son and husband have ADD/ADHD.

Neither one can tolerate SAMe.

However, both of them like Inositol.

You can try SAMe...say for 2 weeks. You should see by then if there is any effect.
At his weight he is an adult.
To start use one 200mg tablet daily in the morning on an empty stomach.
no food for 1 hour. Both of my guys had negative issues by the 2 week mark.
Agitation was the main response.

I do not have ADHD and I love SAMe ( I take it for arthritis).

Good luck. I wouldn't expect much.

As far as other things go... We had a dramatic response to flax oil/evening primrose/fish oil.
We started with one of each for both of them, and eventually dropped the primrose.
My son and husband now both use flax and fish oil daily. They use a double strength enteric coated one found at both
Costco and Sam's club. Also useful are magnesium and B6 to help with the metabolism of the fats.
Removing trans fats is very important, and now that restaurants and food makers are doing this under the new
law, it is easier to do without changing foods too much.
I have an EFA thread here and a magnesium one for you to look over. The links are in a Sticky thread.
There is also evidence that low zinc is present in some ADHDers.

You might want to research some food intolerance. Gluten and casein are the most common ones that impact
behavior.