Does My Cat Have a Thyroid Problem?

Does My Cat Have a Thyroid Problem?

Health & Safety

If you've noticed your older cat is beginning to display signs that are unusual or out of character, such as behavioural or dietary changes, poor coat condition and generally seeming grumpy, they may be suffering from a condition known as hyperthyroidism.


Generally cats are very good at hiding symptoms when they are not well and owners only really see problems arise in the latter stages of illness. With feline hyperthyroidism signs are sometimes a little more apparent. The condition is quite common and mainly affects older cats over the age of about 8. The cause of the condition is too much of the thyroid hormone, thyroxine, being produced by the thyroid gland. The gland is divided into two lobes and is located in the neck on either side of the windpipe. These hormones play a very important part in the cat's body functions by helping maintain their:

  • Metabolism
  • Body temperature
  • Heart rate
  • Blood pressure
  • Gastrointestinal function (bowel movement)

Feline hyperthyroidism can be very serious, with vital organs such as the heart and kidneys placed under greater strain and liable to be damaged, left long enough the condition can even prove fatal. The good news is this disease can be managed with veterinary care and sensible owners! Because of too much of the thyroid hormone being produced, common signs the owner might see are:

  • Increased appetite and thirst - due to the metabolic rate being higher, the more calories the cat will burn, therefore the owner will always think the cat is hungry and thirsty.
  • Weight loss - even though the cat is eating more, because of the way the metabolic rate has increased, there will be no weight gained, in fact most cats with hyperthyroidism lose weight.
  • Over activity - because everything is happening much faster in the cat, owners notice the cat cannot settle and will often be quite jumpy.
  • Nervousness - again owners may notice their cat is quite nervous and may also start getting quite aggressive towards them and other animals in the house - which may be out of character.
  • Weakness - in further stages of hyperthyroidism, although the food intake could be much higher, the cat will not be able to convert the calories into energy, due to the higher metabolic rate. The cat may become weak and even lethargic.
  • Rapid heart rate - because the body is working much harder to deal with increased metabolism, the heart also must work much harder, this can lead to cardiac disease further on.

Not all of the signs will occur in every cat, some may only appear later depending on how long the cat has been ill. Owners who have a cat displaying any of the signs should make an appointment with their vet, as a matter of urgency. It is also very important that the owner answers honestly any questions the vet might ask. Feline hyperthyroidism symptoms are similar to the signs that occur in cats with diabetes and chronic kidney disease, therefore being open with the vet can assist greatly in proper diagnosis.


Although sometimes vets can feel an enlarged thyroid gland, the definitive way to check for the condition is by taking a blood sample and sending it to the laboratory, to analyse thyroxine hormone levels. The blood test, called a T4, will give the vet a level which can be monitored and adjusted with treatment. The level is also the mark to make sure your cat is improving.


At present there are 4 ways of treatment. All should be discussed with your vet to work out the best approach.1. Daily medication with a drug called carbimazole, to slow the hormone production in the gland. By choosing this option with your vet, you need to remember that you have to give your cat a tablet every day for the rest of their life. For medication to work correctly the tablet also needs to be given about the same time every day. Your vet will want to monitor the cat at regular intervals, with blood tests to check the levels of thyroxine to determine whether the dose is correct. These visits are vital to the success of daily medication and once the level is stable, visits to your vet will be less frequent.2. Radioactive iodine therapy - radiation to treat abnormal cells in the thyroid gland. This treatment is very safe and is the most effective for feline hyperthyroidism. At present there are at least six centres across the UK offering this treatment. The main disadvantage is that your cat will have to spend 2 to 5 weeks hospitalised at one of the centres and there is only minimal contact with your cat for radiation safety reasons. Because of limited availability this option is very expensive.3. Thyroidectomy surgery to remove either one or both lobes of the thyroid glands. This option would only be completed when your cat has been stabilised by drugs. Of course surgery does have risks with anaesthesia and this risk is increased if there are heart and kidney problems associated with the disease. It is also worth knowing that some thyroid tissue may be left behind.4. The newest method is by using a prescription diet that is low in iodine to help maintain thyroid function. This method must mean your cat only eats the special diet and absolutely nothing else. If your cat is the type likes to chase mice and eat them, then even this might affect the way the food works! Although this option sounds straightforward it can work out expensive.


Once your cat has been treated successfully, they will gradually return to being the correct weight, eating and drinking properly, have a better coat and be generally much friendlier! Because feline hyperthyroidism cannot be cured only managed, owners still need to be on the lookout for the original signs and their vet should remind them of this. If the cat shows any worrying signs then blood tests should be repeated to determine the thyroxine level for re-stabilisation.

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