Practical experience is that people cycle through ADHD and depression meds. I agree that it's hard to tell what that means because we don't generally do long term double blind placebo studies.

The issue here is more complicated than just a lack of long term RCTs. It's that we're talking about psychological acclimation within individuals. Given that people's lives change so much, even within an RCT design it's not clear how you get an actual comparison of "effectiveness" from year 0 to year 4.