I would also say that ADHD meds are much more susceptible to this, because the psychological effect is just so noticeable. Taking Vyvanse by itself compared with taking it with a little snack it makes quite a difference in the absorption for me; when I take it with Psyllium husk, then...
EDIT: I guess I should expand on the effects of Psyllium. I mean the meds take longer to kick in
I am in a similar situation as you and trying to figure out the best way to take my medication. I never really thought about my psyllium husks having an effect, so I'm very curious what you've noticed
From what I read it doesn't seem like a good idea to take psyllium husk together with other medications. They seem to recommend one hour or two of interval between it and other meds. I don't know if it's just doctors being cautious, though.
I usually take Vyvanse just by itself at around 7AM just before walking to the gym, so I guess I associate the effect kicking in to my walking back home. On the days I ate something together with it, or specially with Psyllium, I notice a diminished effect
EDIT: I guess I should expand on the effects of Psyllium. I mean the meds take longer to kick in