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Hyperthyroidism in Cats: Signs, Diagnosis & Treatment

What does the Thyroid do?

The thyroid gland is a muscle located within your cat's neck near its voice box, and it is comprised of two separate lobes that sit on either side of the trachea. It is responsible for producing thyroxine hormones that control your cat's metabolism and temperature.

What is Hyperthyroidism?

Hyperthyroidism occurs when your cat's thyroid gland overproduces thyroid hormones, increasing their metabolic rate. It is a disease most common among middle-aged cats above 8 years old.

What are the clinical signs of Hyperthyroidism?

The most common symptoms of Hyperthyroidism are:

  • Weight loss

  • Increased appetite

  • Increased thirst

  • Excess urination

  • Vomiting

  • Diarrhea

  • Hyperactivity

  • High Blood pressure

How is Hyperthyroidism Diagnosed?

Your veterinarian will diagnose your cat based on clinical signs and through careful diagnostic testing. If they suspect that your cat has hyperthyroidism, they will conduct a blood test that will measure the level of T4 hormones in your cat's bloodstream. If necessary, your veterinarian may also perform supplementary tests to gain additional information towards forming a diagnosis. The complete list of possible tests include:

  • Blood chemistry

  • Urinalysis

  • ECG

  • Blood Pressure

  • Radiographs ( X-rays)

How is Hyperthyroidism Treated?

There are several methods of treatment for hyperthyroidism with varying levels of cost and commitment. These methods include:

Oral Medication

Lifelong administration of the drug methimazole which can help regulate the effects of an overactive thyroid. This approach takes several weeks for your cat's thyroid levels to return to normal and involves lifelong administration of the drug, which may be difficult for some owners to maintain. Cats may also experience vomiting, anorexia, fever, or lethargy while on the drug.

Radioactive Iodine Therapy

Radioactive Iodine is injected into your cat's bloodstream and absorbed by the thyroid gland, destroying any abnormal thyroid tissue. This method doesn't require any anesthesia and eliminates the need for daily medication. However, it is only available at specially permitted facilities that are licensed to handle radioactive iodine.


This method involves the complete removal of the thyroid glands. It involves the use of anesthesia, which may put older cats with underlying health conditions at risk. This option is rarely used however due to the effectiveness of medication and radioactive iodine therapy.

Prescription Diet

A veterinarian-prescribed low-iodine diet can lower thyroid hormone concentration levels. This is a non-medicated diet that controls the level of iodine in your cat's food. The prescribed diet should be the only food given to your cat to ensure recovery.


While Hyperthyroidism can be scary for you and your cat, it can be managed, allowing them to live a long fulfilling life. If you have any questions regarding Hyperthyroidism or believe that your cat is Hyperthyroid, call us at

559-434-5470 today to learn more or book an appointment.



  1. VCA Animal Hospitals. Hyperthyroidism in Cats.

  2. Cornell Feline Health Center. Hyperthyroidism in Cats.

  3. Veterinary Continuing Education Consulting and Control. Top 10 Signs of Hyperthyroidism in Cats.

  4. FDA. Hyperthyroidism in Cats - There is an FDA-Approved Drug to Treat it.

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