I don't know about the one thing you mentioned, but I be worried about using something that isn't approved.

I do have a dog with thyroid problems. Preacher takes thyroid meds for hypothyroidism. His symptoms prior to the diagnosis were he was extremely lethargic, grouchy with other dogs, gaining weight despite no changes in his food, his fur was falling out in clumps and what was left was dry and brittle.

He's been on the meds for almost a year now. His coat took the longest to come back to normal. I noticed a change in his energy levels and mood within days of starting the pills.

The medication is cheap and easy to give. I just hide the pill in a chunk of cheese twice a day. have to be careful not to give him too much though as dogs with thyroid problems still tend to gain weight very easily.

Make sure your vet runs a full thyroid panel on the blood work. A general health panel will not show his true thyroid function and you may end up medicating him for something that is not the problem.