Free vets online with code WAMIZ20


Everything you need to know about hyperthyroidism in cats

Ginger cat getting checked at the vet advice
© Shutterstock

A scruffy coat, sudden weight loss and the constant need to pee? If you’ve noticed these signs in your cat, they might have an overactive thyroid. Here’s everything you need to know about hyperthyroidism in cats.

By Alice Lang

Updated on the 19/12/2019, 15:28

Hyperthyroidism, also known as an overactive thyroid, happens when a cat’s thyroid gland releases excess thyroid hormones. This causes pretty much everything in the body to speed up, up and up - and with it, brings a whole host of symptoms and problems.

An overactive thyroid can make your cat seriously ill and if it’s left untreated, can even lead to death. Thankfully, in most cases, cats can make a full recovery if the condition is detected early.

What is hyperthyroidism in cats?

“Hyperthyroidism is the veterinary term used to describe an illness resulting from having excessively high blood levels of thyroid hormones. All cats have a thyroid gland composed of two portions (referred to as thyroid ‘lobes’) in their neck.” explains Sarah Caney in Caring for a Cat with Hyperthyroidism.

“The thyroid hormones are required in healthy cats for many functions including normal growth and development and maintenance of a normal metabolic rate. Excessive blood levels of thyroid hormones are (such as is the case with hyperthyroidism) are damaging to the body and ultimately, this is a fatal illness if not treated

Feline hyperthyroidism causes and risk factors

hyperthyroidism in cats
Is your cat restless and then suddenly tired? They might have an overactive thyroid ©Pexels

Is your cat getting old? They’re at risk of hyperthyroidism. According to Caring for a Cat with Hyperthyroidism, the most common age group being diagnosed is 10-13 years old. It’s highly unusual for a cat under 7 to be diagnosed with the disorder.

It’s believed that male and female cats are affected with an equal frequency - so you’ll need to keep an eye out for hyperthyroidism in cats no matter what your kitty’s gender.

The underlying cause of an overactive thyroid in cats is unknown, but it’s normally caused by a benign change - that means it’s non-cancerous. However, in very rare cases, a cancerous tumour is to blame.

Symptoms of hyperthyroidism in cats

Hyperthyroidism in cats is usually pretty obvious. The symptoms may be minimal at first but can become severe as the disease progresses.

Keep an eye out for the following signs and symptoms of hyperthyroidism in cats - especially if your cat is 10 or older:

  • Unexplained weight loss
  • Increased urination
  • Increased thirst and appetite
  • Irritability and nervousness
  • Fast heart rate
  • Scruffy, matted coat
  • Restlessness
  • Diarrhoea and vomiting
  • Panting
  • Weakness or lethargy
  • Lumps and nodules in the neck

Complications of hyperthyroidism in cats

It’s essential to get hyperthyroidism treated as soon as you can. Otherwise, the consequences can be rather severe - including heart failure, damage and death. Thyroid hormones influence virtually every organ in the body. Let’s take a closer look.

If left untreated, overactive thyroid in cats can damage the heart, altering the muscular wall and eventually leading to heart failure. High blood pressure is commonly seen, too, which can cause further damage to several of the body’s organs.

Hyperthyroidism and kidney disease in cats are closely linked. Although kidney disease isn’t directly caused by an overactive thyroid gland, the two diseases are often seen together. An overactive thyroid will often have a negative effect on the function of the kidneys, making the condition even harder to manage.

But, there’s good news - with treatment, the complications of hyperthyroidism in cats are potentially reversible!

Treatment of hyperthyroidism in cats

hyperthyroidism in cats
Surgery? Nope... not today! ©Pexels

As soon as you notice any signs of hyperthyroidism in cats, get your cat to the vet and voice your concerns. Your vet will be able to run a simple blood test which measures the hormone levels in your kitty’s blood - if it’s high, your cat has an overactive thyroid gland.

Treatments for hyperthyroidism in cats vary but could include:

Oral medication

There a number of medications available which aim to lower the level of thyroid hormone in your cat’s blood. This is the most common treatment for hypothyroidism in cats and is usually administered in the form of a tablet or gel applied to the skin.

It usually improves the condition within 3 weeks, but side effects such as vomiting, loss of appetite and tiredness often appear. However, to keep the condition stable, the medication needs to be taken for the rest of your cat’s life.

Radioactive iodine

This is a rather expensive treatment option but is also the safest and most effective.  It’s administered in the form of an injection with no anaesthesia required. Your cat's hyperthyroidism will be cured forever once they've had the treatment - yep, it's magical!


Sometimes, an operation to remove the thyroid gland is an option - but it’s not always effective. Tumour cells might be present in other parts of your kitty’s body which will continue to produce excess thyroid hormones, despite the removal of the gland. However, this complication is rare, so it’s still a fantastic option - surgery is usually less costly in the long run.

If your cat is suffering with hyperthyroidism, we wish them all the best. We're sure they'll make a swift recovery and lead a long, happy and purrfect life!