I have a 15 year old I rescued last year with high blood pressure, kidney failure AND hyperthyroidism. He's being seen by a holistic vet and being treated by Methimazole for the hyperthroidism (the medicine is compromising his kidneys) and another med for his blood pressure. He's not in any pain.

That's the thing...if he was in any pain, I'd definitely re-think the whole thing, but he's not. Probably best to ask your vet. My vet put Barty on an appetite stimulant but he won't eat his food when I put it on his food. So I stopped. I'd rather demand feed him canned food then try and force him to take a stimulant he doesn't like (it wastes food too).

You and Princess will be in my thoughts and prayers.