Duplicate post, threads merged.
He did hurt his back about a month and a half ago and I do believe he has been under stress because of it. He wouldn't go up the stairs in the back to come inside. I had to get him all the way around the side of the house every time he went out. Just three days ago he got the courage to go up the stairs again. Today he is not panting as much and seems to be doing alot better.Talk to your vet.
Some dogs pant because they are not cooling themselves efficiently.
Dogs also pant when they are stressed - sometimes that stress is due to pain/discomfort.
I should have mentioned his weight. He weighs 117 lbs. Yes I know that is alot, but he gets his daily exercises and is losing it slowly. We went to the vet today but he was out of town and won't be back until Friday. We only have two vets where I live and I don't trust the other one (bad experiences with him before) so we will wait until Friday. He is doing alot better today. We gave a cool bath last night and it seemed to have helped, he is still panting but not like before.If your dog is being given as much thyroxine as you state, then he is being seriously overdosed. That is why he is panting. Please contact your vet now, and I do mean now, and discuss in detail how much you should be giving. My dog gets .5mg twice a day. What you are describing is a huge overdose. If your vet tells you to keep him that high, please find another vet fast!