It has often been claimed (here and elsewhere) that vets are better at handling thyroid issues than doctors. I happened across this link the other day and, after some vacillation, have decided to post a link.
Don't blindly take this as being applicable to humans! It is for interest and comparison - not advice on treating yourself.
In hypothyroidism, impaired production and secretion of the thyroid hormones result in a decreased metabolic rate. This disorder is most common in dogs but also develops rarely in other species, including cats, horses, and other large, domestic animals.