The most common sign of hyperthyroidism in cats is weight loss despite an increased appetite. Other common signs include vomiting, diarrhea, hyperactivity, drinking and urinating more than normal, and an unkempt hair coat. Because the disease develops gradually, signs are often easy to miss at first.

Do cats with hyperthyroidism suffer?

This is because the cat’s heart must work harder to match the state of its overactive metabolism. This means that in addition to years of dietary distress, general restlessness and nervousness, and hair loss, a cat whose feline hyperthyroidism is untreated can suffer from heart problems that can be fatal.

What happens if you don't treat hyperthyroidism in cats?

Feline hyperthyroidism is a common endocrine disorder in older cats, caused by the overproduction of thyroid hormone. Left untreated, hyperthyroidism can result in heart failure and other complications, and can even lead to death.