Aloha! You're speaking with Dr. Michael SalkinLeaving your cat with his vet for the day to have a glucose curve performed (serial blood sugar measurements throughout the day) will tell you if he's being overdosed. We look for a curve indicating the Somogyi effect - a profound drop in blood sugar (hypoglycemia) following insulin administration followed by an exaggerated rebound effect to hyperglycemia. Be sure that his vet also checks for hyperthyroidism - a very common cause of polyphagia (increased hunger) yet weight loss at his age - and a disease that can exist concomitantly with diabetes and make regulation of these cats quite difficult until the hyperthyroidism is well-controlled.Please respond with further questions or concerns if you wish.
He has already had a glucose curve. He gets too stressed, and the results are inaccurate that is why he goes back every 3 weeks to have blood tests to see how the insulin is working. He has also been checked for hyperthyroidism and does not have that either.