KD976, I think your DH is not wrong to feel as he does about meds; I know that at that age we felt it was a drastic measure for a small child, and we weren't there yet. Especially since you don't have a solid dx yet, it is within the bounds of reason to be extremely cautious.
Here's a strategic question: how much time does your DH spend with your son? Does he take him to scouts/ supervise him in church or supermarket/ deal with him in situations that require DS to pay attention? If not, you might want to arrange for some of that kind of time, just so your DH has some of the same experiences you have had.
I found that spreading out the responsibility for supervising DS made us observe the same issues, which means we have been able to be more unified when it comes to treatment options. If DH happens to be in denial because he hasn't seen what you've seen, then letting him experience the difficulties might help.
Best,
DeeDee
