I have multiple dogs on thyroid meds. Never seen one negative side effect in any of them.

The thyroid affects a vast range of things in the body. All of my dogs had different initial symptoms, Earle was grouchy and snappy, Preacher was lethargic and always cold, Chum collapsed at random intervals! All have the same condition, hypothyroidism. I've got to the point that whenever I take a dog in for just about anything, I ask for a thyroid panel too!