My RB Boo was on methamezole for hyperthyroidism and he did well w/it once we got the dosage figured out which took a while. Boo was 19 1/2 when he passed and he'd been medicated for a couple of years before then. He lost a lot of weight, too, but after a while I realized that it was b/c of his age and nothing more. When he died, it wasn't from hyperthyroidism; he had bladder cancer, so I wouldn't want to give you the wrong impression. If we knew how old Bella is, that would help and maybe you could postpone your decision until you know a little more. Please understand, I'm not asking you to decide not to have her PTS but just saying that, if she's younger, maybe there are alternatives. This is for you and your vet to discuss, of course. Please let us know Bella's age. I probably haven't been much help to you but I do know that hyperthyroidism is tricky and it sometimes takes a while for things to calm down. Keep the faythe.