My dog's on synthroid. I don't mean to make fun of your condition, but she was transformed in about two doses. She was 7 years old, had gained weight, wasn't eating and didn't have any energy at all. We thought she was just aging, but a blood test revealed the problem and the change was amazing.
Bonus: She lost 20 percent of her body weight, regrew a thick, luxurious coat and it costs $18 a month from the most expensive vet in town.