Hyperthyroidism in Cats: Signs, Symptoms, & Treatment

Four Minutes Mar 02, 2023

Keeping pets healthy can be a challenge — especially cats. Indoor cats can live very long, happy lives but their elusive natures can make it difficult to notice when they’re sick. Hyperthyroidism is one of the most common illnesses indoor cats experience. Here are the facts about the disease, what pet parents should look out for, and how it’s treated.

What Is Feline Hyperthyroidism?

Feline hyperthyroidism is caused by the overproduction of hormones from a cat’s thyroid gland.¹ Thyroid glands are a pair of butterfly-shaped glands located on either side of the windpipe. This affliction is one of the most common hormonal disorders in middle-aged and senior cats.

Hyperthyroidism can be commonly caused by a benign tumor on one or both thyroid glands. Most cases of hyperthyroidism are mild, with many cats not showing any signs of the illness.¹

What Are the Symptoms of Hyperthyroidism in Cats?

Cats who do experience symptoms of hyperthyroidism are usually 8-years-old or older. Every cat’s symptoms look a little different. Your cat may exhibit one, some, or even all of the symptoms associated with it, which makes it difficult for pet parents to diagnose it on their own..

With this in mind, it may be helpful to think of the clinical signs of hyperthyroidism based on the most common symptoms to the least common symptoms. This knowledge can help you discern whether you should take your kitty to the veterinarian.

The most common hyperthyroidism symptoms in cats can include:

  • Weight loss
  • Excessive appetite
  • Increased urination and thirst
  • Vomiting
  • Diarrhea
  • Increased fecal volume
  • Hypersensitivity
  • Unruly or unkempt fur

The least common signs of hyperthyroidism in cats can be heart issues. Some of these cardiovascular issues can include:

  • Increased heart rate
  • Heart murmurs
  • Shortness of breath
  • An enlarged heart
  • Congestive heart failure

Keep in mind that hyperthyroidism can be a progressive disease. That means that it may take several years for a cat to experience complications from hyperthyroidism.

It can be likely that you’d notice common symptoms, such as rapid weight loss and diarrhea. Addressing these sorts of behaviors will usually have you at the vet’s office long before heart complications could set in.

Diagnosing Hypothyroidism in Cats

To diagnose hyperthyroidism, your vet may perform a physical exam that focuses on your cat’s throat.¹ They’ll look for any lumps or masses that may indicate that a tumor is present. After the exam is done, your vet should discuss behavior that you’ve noticed at home — such as vomiting or lack of energy.

Lastly, your cat’s hormones will usually be measured using a common blood test. This test will measure the amounts of T3 and T4 (iodine-containing hormones) in your cat’s blood sample.¹ Depending on your veterinarian’s office, It’s likely that your vet’s assistants can do this test in-house, so you might get the test results quickly. That said, it might still take a few days for the sample to be thoroughly tested and examined.

What Does Hyperthyroidism Treatment for Cats Look Like?

Vets may choose to manage the hormonal disorder with simple lifestyle changes, medications, surgery, or a combination of all these approaches. Here’s what treatment of hyperthyroidism in cats could look like.

Lifestyle changes

Once you’ve received your diagnosis, your vet should work with your family on lifestyle changes. You should work together to gain control of hyperthyroidism. One option is to feed your cat veterinary prescription diets. These diets are low in iodine, which can help minimize their symptoms.¹

At the same time, pet parents are encouraged to get their cats to exercise more. Talk to your vet about ways to boost your pets energy levels or manage their play time throughout the day.

Medications and therapy

Medications for hyperthyroidism in cats are prescribed on a case by case basis. Currently, there’s only one FDA approved medication to treat feline hyperthyroidism called methimazole.¹,² The brand name of methimazole is called Felimazole.² The dosage may vary but typically a cat is given this oral medication twice a day, every 12 hours.¹,²

Another option may be something called radioactive iodine therapy.¹ This therapy works by injecting iodine into the thyroid glands, which destroys the overactive tissues. Pet parents should know that this method is often considered safe, simple, and effective for most cats.


Your vet may suggest surgically removing any tumors found on your cat’s glands. Some cats don’t qualify for surgery because of their age and health. For example, if your cat has liver disease and they’re diagnosed with hyperthyroidism, your vet may think it’s too risky to perform a surgery.

The reason? If parts of both glands or all of the glands are removed, your pet will have to take hormone replacements for the rest of their life.¹ These hormonal medications have side effects that can impact their lifestyle and how well their organs function. It’s recommended to weigh your pros and cons with your vet before deciding to move forward with such a procedure.

MetLife Pet Insurance Doesn’t Compromise. Neither Should You

Pet parents try their best to take care of their cats so they can live long lives. As cats enter their golden years, they may develop diseases like hyperthyroidism. Luckily, hyperthyroidism in cats is common and treatable, so vets across the country are ready and able to care for your pet.

That’s why cat insurance policies can cover things like labor, prescription food, and surgical costs, depending on your policy. You can choose the best professional so you don’t have to compromise on medical care. Get started today with a free quote from MetLife Pet Insurance, winner of the “Pet Insurance of the Year” Award in the 2022 Pet Independent Innovation Awards Program.

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¹ “Disorders of the Thyroid Gland in Cats,” Merck Veterinary Manual

² “Hyperthyroidism in Cats —There’s an FDA-Approved Drug to Treat It,” Federal Drug Administration

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