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Hyperthyroidism in Cats: Treatment Options

Middle-aged and senior cats often experience hyperthyroidism. Our Gaithersburg vets define this common health issue and discuss symptoms and treatment options.

Thyroid Hormones & Your Cat's Health

Overactive thyroid glands cause hyperthyroidism in cats. This very common endocrine disease is marked by an increase in the production of thyroid hormones, which leads to a variety of symptoms that can make your cat severely ill. LINK TO OTHER HYPERTHYROIDISM POST

Thyroid hormones regulate many processes throughout the body and control the matabolic rate. When too much of the hormone is produced, clinical symptoms can be quite dramatic. 

Cats that suffer from hyperthyroidism tend to burn energy too quickly, which leads to weight loss despite the fact that your kitty is eating more food due to an increase in appetite. We'll discuss more symptoms below. 

What are symptoms of hyperthyroidism in cats?

Hyperthyroidism is typically diagnosed in older cats between 10 – 13 years of age. A cat's gender – male or female – doesn't appear to be a factor in whether they develop hyperthyroidism. 

Common symptoms of hyperthyroidism in cats include:

  • Increased restlessness or irritability 
  • Poor grooming habits 
  • Increase in heart rate 
  • Increase in thirst 
  • A healthy or increased appetite 
  • Anxiety or nervousness
  • Vomiting or diarrhea
  • Vocalizing

Not all cats with hyperthyroidism display the same symptoms. These signs are also usually subtle at the onset of hyperthyroidism and gradually become worse as the disorder progresses.

Other diseases can also complicate and mask these symptoms. This is why it's important to book an appointment for a physical exam with your vet when you first start noticing physical or behavioral changes in your cat, so any abnormalities can be addressed earlier rather than later.

How is hyperthyroidism diagnosed?

Diagnosing hyperthyroidism in senior cats can be challenging. Your vet will complete a physical exam and palpate your cat’s neck area to look for an enlarged thyroid gland. A battery of tests may be required to diagnose hyperthyroidism in your cat, as many other common diseases experienced by senior cats (intestinal cancer, chronic kidney failure, diabetes, inflammatory bowel disease and more) share clinical symptoms with hyperthyroidism.

Blood tests and diagnostic imaging such as a chest X-ray, electrocardiogram or ultrasound may also be required. LINK 

Treatment & Medication for Hyperthyroidism in Cats

When it comes to successfully treating hyperthyroidism in cats, your vet may consider a few different approaches. First, the veterinarian will assess your feline friend's specific needs and circumstances, and weigh the advantages and disadvantages of each of the four options: radioactive iodine therapy, medication, surgery, and dietary therapy. 

Treatment for hyperthyroidism in cats may include:

Radioactive Iodine Therapy 

Also referred to as I-131therapy, radioactive iodine therapy is likely the safest and most effective treatment option. The body requires iodine to produce both T3 and T4, two important thyroid hormones. 

During treatment sessions, your veterinarian will inject radioactive iodine into your cat's body. The iodine makes its way through the bloodstream to the thyroid gland, where radiation destroys abnormal thyroid tissue without destroying surrounding tissue or disturbing the parathyroid glands. Within one to two weeks of treatment, most cats treated with radioactive iodine have normal hormone levels. 

While radioactivity carries no significant risk for the treated cat, you and anyone who will be in close contact with your cat will need to take precautionary protective measures. Your cat will need to stay in hospital for between three and five days after treatment. Due to strict treatment guidelines, most facilities will not allow visitors during this quarantine period. 

Also referred to as I-131 (radioiodine) therapy, this form of nuclear medicine is highly successful at curing hyperthyroidism in cats with only one treatment. In rare cases, some cats may need a second treatment.

Antithyroid Medication 

Anti-thyroid drugs curb the production of thyroxine by blocking reactions that trigger the production of the hormone. You would need to administer pills orally twice a day. Your vet will need to examine your cat periodically to check hormone levels and adjust the dosage if required. 

While these drugs are usually effective, they may be required for the rest of your cat's life. There is also the risk of adverse reactions (as with any drug), which include liver problems, facial swelling and itching, loss of appetite, bleeding, vomiting, and depression. Long-term use is discouraged because the thyroid tumor continues to grow and these medications may eventually stop working. 

Dietary Therapy 

Some studies have suggested that for some cats with hyperthyroidism, restricting the amount of iodine in the diet decreases the production of thyroxine by the thyroid gland by limiting the amount of iodine needed for thyroid hormone production. While this type of diet may help treat this disease, cats must eat only this diet for the rest of their lives with no supplementation with other foods, treats, or hunting.

If your cat has other health conditions that make other treatment impossible, your vet may consider dietary therapy. 

However, there is some debate around this treatment option, as the effects of long-term iodine restriction can negatively impact overall health. It's also possible that this option won't have the desired effect, and your cat's hyperthyroidism symptoms may even worsen. Consult your veterinarian about these issues if you're considering dietary iodine restriction as treatment for your cat's disease.   


Surgically removing the thyroid glands (thyroidectomy) is a relatively straightforward surgical procedure with a good success rate. Surgery can often eliminate symptoms for the long-term or permanently cure the disease, eliminating the need for long-term medication.

However, surgery does come with risk – the parathyroid glands are close to or within the thyroid gland, and could be inadvertently damaged during surgery. Because these glands are important for maintaining stable blood calcium levels, damage can negatively affect your cat's long-term health. Medication and radioactive iodine therapy are just as effective at treating hyperthyroidism in cats, and are less invasive. Surgery is rarely recommended for treating this condition. 

What can happen if my cat's hyperthyroidism is left untreated? 

Left untreated, hyperthyroidism can affect the function of the heart, change the organ's muscular wall and increase heart rate. This often results in heart failure. 

Cats that suffer from hyperthyroidism also often experience high blood pressure (hypertension). Though we see this less often, it can cause damage to several organs, including the heart, brain, kidneys, and even the eyes. If your vet diagnoses your cat with hypertension in addition to hyperthyroidism, medication will be needed to regulate blood pressure. 

Prognosis & Recovery for Hyperthyroidism

Feline hyperthyroidism requires long-term treatment and management. That said, prognosis for cats with this disease is generally good with appropriate therapy. However, any damage to other organs caused by hyperthyroidism can reduce your cat's longevity. 

All treatment options carry the risk of potential hypothyroidism, which requires daily thyroid hormone supplementation. 

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet.

Do you suspect your cat has hyperthyroidism or another internal medical condition? Contact our Gaithersburg vets to book an examination.

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Veterinary Referral Associates is accepting new patients! Our experienced vets are passionate about the health of Gaithersburg companion animals. Get in touch today to book your pet's first appointment.

Contact (301) 926-3300