Thanks, everyone! Your kind replies mean so much to me. I stopped the B12 because Mac is now eating me out of house and home! Nothing wrong with his appetite now. The vet says Pepcid can't hurt him and many older cats start this vomiting when their kidneys start to go. Funny thing is, he doesn't drink an extraordinary amount, nor does he urinate too much. He seems pretty normal in those aspects. His last blood work shows slightly elevated liver values, but nothing going on with his kidneys. My vet just increased his methimazole dosage and took a "let's wait and see" stance. Anyway, we are going in for another blood workup next month, so maybe we'll get an answer to his tummy problems. For now, he is acting fine and begging for food once again!