How to Spot the First Warning Signs of Feline Hyperthyroidism

What is Feline Hyperthyroidism?

The two thyroid glands in cats are responsible for the production of a number of hormones which regulate the metabolism and are involved in the function of all the body’s major organs. Healthy thyroids are therefore essential for the general health of your cat.

The condition known as hyperthyroidism occurs when one or both of the thyroid glands become too active, and produce excess amounts of a hormone called thyroxine (T4).

This is usually a treatable condition and diagnosis is typically uncomplicated with blood testing. If you suspect that your cat may be affected you should seek qualified veterinary advice as soon as possible.

What Kinds of Cat May Be Affected?

All breeds can suffer hyperthyroidism, but it is generally something which affects older animals.

Less then 10% of cases occur in cats of less than 10 years of age, and the average age for the onset of the condition is 12 years.

How Can I Tell if My Cat Has the Condition?

An over-active thyroid leads to an increased metabolic rate. Weight loss, increased vocalization, hyperactivity, increased appetite, vomiting and soft stool are characteristic early symptoms. But any of the body’s organs may be affected, and a wide range of symptoms can develop.

You may notice a rapid heart rate and changes in behavior such as restlessness or aggression.

Digestive disturbances such as vomiting, diarrhea and more frequent visits to the litter box are also sometimes apparent.

Less common symptoms may include breathing problems and muscular weakness.

How is Hyperthyroidism Diagnosed?

In some cases enlarged thyroid glands in the neck may be detectable to the touch of an examining vet, but the other symptoms of hyperthyroidism can be caused by a wide variety of other conditions.

The level of thyroid hormone in the blood is a key diagnostic measure. Thyroid levels sometimes fluctuate, so multiple blood tests may be required before a final diagnosis can be made.

In rare cases, where blood tests are inconclusive, diagnosis may be made by scanning the thyroid glands with specialized imaging technology.

What are the Treatment Options?

Hyperthyroidism can have serious health implications for your cat, including heart and kidney disease, so it is very important that the appropriate treatment is applied as soon as possible.


Orally administered drugs are often effective in reducing the blood levels of the thyroid hormones. The disadvantage of these medications is that the hormone levels will rise again if the treatment is discontinued, and affected cats must generally stay on the drugs for life.

Radioactive Iodine

A specialized treatment may be the administration of radioactive iodine. The compound travels through the bloodstream to destroy the thyroid tissue while allowing the thyroid glands to continue their normal hormone production.

This is a safe and effective procedure, but it has the disadvantage of requiring the cat to remain hospitalized for a period of time.

Find Out More

Hyperthroidism is a serious condition, but it generally responds very well to treatment, so if you are concerned that your cat may be suffering from thyroid problems, or have any questions about the information above, please call (480) 968-9275 or visit us at