What is hyperthyroidism? How to spot and treat it hyperthyroidism in cats

Updated 11/12/2023

Hyperthyroidism is a relatively common illness in felines, particularly middle-aged and older kitties. Like most aging animals, thyroid issues in cats are something that can simply occur due to old age and reaching their golden years. Whilst hyperthyroidism in cats sounds scary, it can be treated especially if spotted early on.

We collected some key kitty facts on hyperthyroidism, how to recognize feline hyperthyroidism, and treatment options for poorly paw purring putties. 

What is hyperthyroidism in cats?

According to PetMD, hyperthyroidism is:

“Hyperthyroidism in cats is a disease that’s usually caused by a benign tumor within the thyroid gland. This tumor causes an overproduction of the thyroid hormone called thyroxine. One of the primary functions of this thyroid hormone is to regulate an animal’s metabolism.” 

This means a cat’s stomach begins digesting food too quickly, which leads to an increased appetite but they experience severe and sudden weight loss. If left untreated, this can cause other dangerous illnesses to develop like high blood pressure, heart disease, and kidney disease.

Most diagnoses are made in older cats above the age of 10, with many kitties developing this illness at about 12 years old. Vet checks on middle-aged and older cats will include blood tests for hyperthyroidism if they’re showing symptoms or their pet parents are concerned.

Symptoms of hyperthyroidism in cats

There’s quite a long list of symptoms of hyperthyroidism. Pet parents will often notice a change in their purr babies as they age, so it’s important to keep your vet as up-to-date as possible on any new behaviors or habits.

Hyperthyroidism is common in cats, so here’s a list of potential clinical signs to look out for:

• Increased appetite - many cats are food-focused felines, so this may be hard to spot. However, if they are suddenly eating a lot quicker than usual and have ravenous appetites, this is something worth telling the vet about.
• Weight loss - particularly if it happens very suddenly and rapidly.
• Increased water consumption - again, keep an eye on their water bowl levels.
• They’re urinating more often.
• Increased meowing or yowling.
• Vomiting and diarrhea.
• Hyperactivity or easily overstimulated more than usual.
• Increased aggression or anxious behaviors.  

As we always say, if you notice any changes in your cat's behavior or pet sitting paw pal, contact their vet immediately.

Hyperthyroid medication and treatments

Your vet will suggest either hyperthyroid medication, radioactive iodine therapy or surgical removal of the thyroid glands. This will depend on how far along your cat’s illness is and whether it’s affected other parts of their body.

Methimazole for cats is the most inexpensive of the three options and is often used as a first solution for an early diagnosis of hyperthyroidism in cats. It also has the least amount of side effects making it a more pleasant experience for your fluffball.

Radioactive iodine therapy is often a vet’s go-to treatment for hyperthyroidism because of how effective it is. However, if your cat has other health problems or a weakened immune system, this can be a risky option. Your vet will always know best, so be sure to ask them as many questions as possible about why this could be the best option.

Finally, your vet may decide surgical removal of the thyroid glands is the best way forward. This will take away the cause of the problem - the enlarged thyroid gland - and will stop this disease from returning. However, surgery is another risk to cat health, especially in older cats. The anesthetic and stress put on a cat’s body during surgery can lead to hyperthyroidism complications.

It’s important to note that hyperthyroidism can be a symptom of another health issue in your kitty. Your vet will likely ask you to do additional tests to check other areas of your cat's body.

Meet our veterinary expert, Aisling

This article has been checked by veterinarian Aisling O’Keeffe MVB CertSAM ISFMCertAdvFB. Aisling qualified as a vet 7 years ago from University College Dublin. She has worked in a mixture of UK small animal hospitals along with Irish practices. She worked for 3 years in a feline-only hospital where she further developed her feline medicine and surgery skills. She currently lives and works in a small animal hospital in Cork, Ireland. 

Both Standard and Premium TrustedHousesitters members have access to our 24/7 Vet Advice Line service if they ever have any health concerns about their paw pals. Similarly, our community forum (which is open to everyone) is a great place to chat with fellow cat carers and swap tips on how to help our feline friends.