Depression rather than ADHD, but I have a (not extraordinarily uncommon) gene mutation that keeps me from properly metabolizing folate (vitamin B9), which means that my antidepressants weren't working properly. I have to take a modified vitamin supplement (l-methylfolate) daily along with my cocktail of antidepressants and mood stabilizers.

It doesn't make me magically awesome, but it helps more than you'd think. So maybe check with your doctor to see if there's a DNA test you should get in case there's something that might make a difference.