Actually it could also be tolerance.
My gf uses opiates at most once a month or once every other month on average.
Her dose has gone from 5mg of oxycodone up to 30-40 over the course of a year or 2.
Note that's with her only dosing once a month at most.
So tolerance can build even with just occasional usage.
Though in this case it might just be that cocktail of drugs.
I can't guarantee that though as my gf is also on a cocktail...
Abilify, Synthroid, Zoloft & Klonopin so her regimen isn't that different from the ops.
Sorry I don't have a better answer for you, but you can't rule out tolerance.
As she got euphoria, etc. fine at the lower doses while on the above cocktail.
She continues to get the euphoria, etc. she just needs higher doses now.
Even with the once a month regimen.