What is hyperthyroidism?

Hyperthyroidism is an overactive thyroid gland and is very common disorder of older cats. It is caused by an increase in production of thyroid hormones from the thyroid gland, which is situated in the neck. Thyroid hormones are responsible for regulating many body processes and when too much hormone is produced the clinical signs can be quite dramatic, and cats can become very ill.

Signs of hyperthyroidism

Hyperthyroidism is usually seen in middle-aged and older cats, rarely being seen in cats less than 7 years of age. Male and female cats are affected equally. In affected cats, a wide variety of signs usually develop, but these are usually subtle at first, and become more severe over time as the underlying disease gets worse.

The classic signs of hyperthyroidism are:

  • Weight loss
  • Increased appetite
  • Increased thirst
  • Increased activity, restlessness or irritability
  • Increased heart rate
  • Dull coat


Although thyroid glands are usually enlarged with hyperthyroidism, this is not usually visible. Detection of enlarged glands will require careful palpitation. To confirm  a diagnosis, a blood test is needed to measure the level of thyroid hormones in the blood.


Successfully treated cats, irrespective of what treatment is used, will usually have complete reversal of all the signs of hyperthyroidism. Further evaluation will usually be needed to check kidney function and ensure long-term goals of thyroid hormone concentrations are being achieved, but most cats do remarkably well when treatment is administered. There are four main options for treatment:-

  • Anti-thryoid drug therapy which comes in forms of pills or gels
  • Surgery – Thyroidectomy (having the thyroid gland removed)
  • Radioactive iodine therapy – The radioactive iodine is administered as a single injection, usually simply given under the skin.
  • Dietary treatment – A new option that has more recently become available for managing hyperthyroid cats.

If you are concerned about your cat or notice your cat having any signs or symptoms of hyperthyroidism then please contact any of our four surgeries today.