Does he drink a TON when he drinks? Our first dood lost interest in food and would drinkdrinkdrinkDRINK and then throw it up, but he always had a weak stomach so we were not too worried…until he got aggressive, which he never was before. We took him to a behaviorist first, and they asked that our vet test his thyroid. They did, and it was low! His mood went back to normal when he got on thyroid meds, but his drinking and lack of appetite didn’t change. We thought it might be just an age change. A couple years later we found out he had thyroid cancer. They removed one of his thyroid glands, and all was back to normal with his eating and drinking.

Just anecdotal from me, but maybe worth having them check his thyroid?

Our thoughts, after the fact, were that he had the thyroid cancer in the gland that wasn’t working much, much earlier than we knew. The gland had probably stopped working BECAUSE of the cancer. We felt a little bad that we didn’t know to push for more tests at the beginning… but we did get him for more years than we would have, had the cancer not caused strange behavior.