Cat Health


Hyperthyroidism is caused by an overactive thyroid, which in majority of cases is caused by a functional adenoma (a benign tumour that can grow on one or both sides of your cat’s throat).

Signs that your cat may be hyperthyroid can be subtle or more obvious and these include:

  • Eating more – seems hungry all the time
  • Drinking and urinating more
  • Losing weight
  • Yowling at night or disorientation
  • Increased irritability
  • Decrease or increase in grooming
  • Lying on cold surfaces such as tiles and wooden floors
  • Fast breathing
  • Vomiting

 Your vet will diagnose hyperthyroidism based on a combination of patient history, physical exam, blood pressure measurements and specialized blood tests.

There are many treatment options available and a discussion with your vet will determine the best course of action for both you and your cat. If one treatment is not suited to you and your cat or does not work, another can always be tried.

Treatment options include:



These work by inhibiting thyroid enzymes and can be given once or twice daily depending on the type of drug used. Follow up vet visits and repeat blood tests are usually required in the first few months to make sure the right therapeutic dose is reached. Some side effects can be seen with these medications such as vomiting and diarrhea. These may seem like the cheapest option in the beginning but may become costly as time goes on and repeated vet visits, blood tests and prescriptions are required.

Medical management using tablet medications may also be used for stabilization of the patient before other forms of treatment.


Ear creams

These are the same as the tablet medications mentioned above but are applied to the inside of the ear and absorbed transdermally. A great alternative for cats who do not like to take tablets and refuse to eat them in food. These are usually more expensive than tablets as they must be compounded specially.


Radioactive iodine treatment

This is generally considered the best treatment for hyperthyroidism as it is very successful (over 90% of cases only require one treatment), safe, does not require anaesthesia and can treat ectopic thyroid tissue as well as thyroid carcinoma. This is only an option in cats who have responded well to more temporary hyperthyroid medication without any kidney dysfunction developing.



Once a very common treatment for hyperthyroidism it is becoming less desirable due to the risks of accidental removal of the parathyroid gland at the same time resulting in ongoing problems with hypocalcaemia (low calcium) which can be fatal), the risk of reoccurrence of disease via regrowth of thyroid tissue left behind, and the availability of other more advanced options.


Dietary management

There is an iodine-restricted diet on the market used for control of hyperthyroidism. This food has to be used absolutely exclusively for it to work (no treats or human food). This also means keeping your cat indoors so they can not access other sources of iodine and deionized water may also need to be sourced. Even a sneaky lizard or a cockroach snack can derail a restricted iodine diet and make it a complete waste of time and money.

There are not a lot of studies as this diet is quite new but if it can be the sole source of nutrition and your cat likes the taste, there is no reason why this can’t be a good option.