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Published on 30 Apr 2021

Old Ginger cat tired and resting.

Mainly affecting older cats, hyperthyroidism occurs when the thyroid produces an excess of thyroid hormones.

What is Hyperthyroidism?

The thyroid is a gland found in the neck of mammals. The hormones it produces play a vital role in many body processes including metabolism, heart, digestion and muscle functions. In hyperthyroidism, changes to the thyroid mean that it produces more hormones than the body needs. 

Which pets are most affected?

Hyperthyroidism is very common in cats and quite uncommon in dogs.  

According to PetSure data in 2020, Hyperthyroidism is most prevalent in the following breeds of cat: 

Breed Prevalence
Domestic short hair / “Moggie”1.29%
Russian Blue0.53%
British Shorthair0.13%
Maine Coon0.10%

Prevalence = Total number of unique claiming pets / total number of insured pets across 12-month period. Excludes breeds with less than 500 active pet insurance policies.

Signs of Hyperthyroidism

Because the thyroid affects so many body processes, the symptoms of hyperthyroidism can vary between individuals and affect different body systems. 

Some of the more common signs include:

  • Increased appetite and thirst 
  • Weight loss 
  • Cats may be more active, vocal, restless or even aggressive 
  • Reduction in the quality of the coat 
  • A high heart rate
  • Vomiting / diarrhoea 

Less commonly occurring signs include weakness and lethargy. 

Diagnosing Hyperthyroidism

Because the signs of hyperthyroidism may look like many other common problems found in older cats, a variety of tests may be used to rule out other diseases and reach a diagnosis of hyperthyroidism. Blood and urine tests are generally the first point of call. 

Sometimes, the vet can feel the enlarged thyroid gland. In many cases, blood testing can diagnose hyperthyroidism in cats as it will show elevated T4 (thyroxine). In some cases, however the T4 is normal so further blood tests or scans may be needed. X-rays or an ECG of the heart may also be indicated to check for damage caused by the high thyroid hormones.  

Management of Hyperthyroidism 

Hyperthyroidism in cats may be managed with medication, surgery, radioactive iodine therapy or dietary therapy. Radioactive iodine therapy and surgery can be curative, while medication and dietary therapy is likely to be lifelong. Management of any concurrent illness is important, as well as managing any of the complications of hyperthyroidism such as heart disease or high blood pressure. 

Your vet will be able to recommend a plan to manage your pet’s Hyperthyroidism. 

If you are concerned that your pet might be unwell, get in touch with your vet for advice.

How much does it cost to treat?

According to PetSure claims data from 2020 (calendar year), the average, single treatment cost relating to Hyperthyroidism was $214. The highest, single claim cost for Hyperthyroidism in 2020 was $3,691.   

Disclaimer: Reimbursement for these claims would be subject to limits, such as annual benefit limits or sub-limits, benefit percentage, applicable waiting periods and any applicable excess. Cover is subject to the policy terms and conditions. You should consider the relevant Product Disclosure Statement or policy wording available from the relevant provider.


  1. Nelson, R & Couto, 2003, Small animal internal medicine, 3rd edition, Mosby, USA. 
  2. Washington State University, Hyperthyroidism in Cats, accessed on 01/12/20

Terms, conditions, waiting periods, limits and exclusions apply. is issued by The Hollard Insurance Company Pty Ltd ABN 78 090 584 473, AFSL 241436, is arranged and administered by PetSure (Australia) Pty Ltd ABN 95 075 949 923, AFSL 420183 (PetSure) and is promoted and distributed by PetSure’s Authorised Representatives (AR) Pet Insurance Pty Ltd ABN 38 607 160 930, AR 1234944 and Pet Culture Pty Ltd ABN 69 644 613 098, AR 001284860. Any advice provided is general only and does not take into account your individual objectives, financial situation or needs. Please consider the Product Disclosure Statement (PDS) to ensure this product meets your needs before purchasing. PDS and Target Market Determination available at .


Kylie Mitchell

Kylie Mitchell


Kylie Mitchell is a veterinarian with over 17 years experience in animal health and welfare, including in the veterinary and pet insurance industries

She has three rescue cats (Noah, Bei Bei and Meeka), four very old cockatiels and a pond-full of fish.

Kylie Mitchell's Pets

  • MeekaMeeka
  • Bei BeiBei Bei
  • NoahNoah

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