I can add my anecdata to the pile. Treating my ADHD (with medication) helped eliminate most intrusive thought patterns that put me in a depressive spiral.

The meds are not without their side effects. Every now and then I take a break for a week or so just to reset my biology. As my problems with executive functioning return, so does the depression.

I think the moral of the story is that interaction with your doctor should be ongoing. You should not just get a prescription for Adderal or Ritalin and check back with them in 2 years.