My 17 yr old long hair has overactive thyroid. He eats special food to help him with his symptoms. He's been on the science diet food for almost one year, it has been a miracle in a bag. He won't take regular medicine for his illness, stubborn old man. But in the last few weeks his fur is starting to matte up, i see he still grooms himself. I have been clipping his fur off. I really don't want to take him into the vet for this just yet, he hates the ride in it causes him more stress than needed. But I don't know why this is happening, he's eating and drinking normal. Suggestions on the fur issue, or should I just take him in to the vet. Could the food have stopped working?????? Thank you in advance for your help