I don’t know if this might help your case or not…. I have multiple sclerosis and amantadine is one of the 2 “go-to” drugs to battle fatigue. I took it several years ago, before being dx’d with ADD but I didn’t feel like it was really doing anything. I was focused on fighting the fatigue, so I really can’t address its interaction with the ADD….
This is interesting though… I’m on AdderallXR (30mg) and find that it runs out after about 4 hours on work days (I’m a teacher). I may run the amantadine idea by my neuro.