Hyperthyroidism in Cats

Hyperthyroidism in Cats | Animed Direct

Hyperthyroidism is one of the most commonly diagnosed conditions in senior cats. It’s caused by an over-active thyroid gland and can result in a range of symptoms, which we’ll explore in this blog. There are various treatments available to help cats with hyperthyroidism, and in most cases the treatment is successful. This blog will look at the pros and cons of these different treatment options, as well as how to spot hyperthyroidism in your cat, and what to expect if your cat is diagnosed with the condition.

What is Hyperthyroidism in Cats?

A cat’s thyroid glands are located in the neck, and they are responsible for controlling the body’s metabolism through the release of a hormone called T4. Around 5% of cats also have functional thyroid tissue located in other parts of the body (known as ectopic).

If a cat has an overactive thyroid gland, this means it is producing too much T4. This can result in a higher metabolism, speeding up bodily functions. This can have harmful effects on the body, eventually leading to health issues like heart disease and high blood pressure.

Symptoms of Hyperthyroidism in Cats

T4 is responsible for a lot of different functions in the body, so too much of it can affect cats in several ways. A cat with hyperthyroidism may show the following symptoms:

  • Weight loss
  • Increased appetite
  • Increased thirst
  • Vomiting
  • Diarrhoea
  • Behavioural changes
  • Poor coat health
  • Restlessness
  • Rapid heart rate
  • Diagnosing Hyperthyroidism in Cats

Your vet may suspect hyperthyroidism in your cat if they show some of the symptoms mentioned above, and as a result of carrying out a physical examination. The condition can then be diagnosed through blood tests. Your vet will be looking for increased levels of T4 in the blood to confirm their diagnosis.

Hyperthyroidism can sometimes mask kidney disease, another common condition in senior cats. One of the changes in the body that occurs because of hyperthyroidism includes high blood pressure. This is generally damaging to a cat’s health, but in the kidneys, it can compensate for them not filtering blood properly. As thyroid treatment reduces blood pressure, kidney disease can become apparent once treatment starts.

How to Treat Hyperthyroidism in Cats

If your cat is diagnosed with hyperthyroidism, your vet will take you through the different treatments available. These include regular medication, radioactive iodine, surgery, and a special diet.

Regular Medication

Hyperthyroidism in cats can be easily treated through medication. Cats take the medication every day, often two or three times, and it works by blocking the production of the T4 hormone.

The dose needed will vary between cats, and multiple blood tests are usually needed over a few months to determine the correct dose.

Hyperthyroidism medication is available in both tablet and liquid forms. Tablets must be given whole, not crushed, and neither should be handled by pregnant women.

Since this form of treatment works by inhibiting hormone production, it must be given for life – if medication is stopped, symptoms will return. Cats taking anti-thyroid medication usually also need regular blood tests to monitor the condition. However, the costs are spread out across the cat’s lifetime, and it’s a safe and effective form of long-term treatment.

Radioactive Iodine

Unlike the medication discussed above, a single dose of radioactive iodine therapy provides a cure in 90% of cats. It is given as an injection and works by destroying all functional thyroid tissue. This includes functional thyroid tissue located in other parts of the body (ectopic).

It’s a safe and effective treatment with next to no side effects and no ongoing costs. However, the treatment itself is very expensive and only offered in certain specialist centres. Cats who receive radioactive iodine treatment also need to stay in a special unit for a couple of weeks after treatment, and cats with concurrent medical conditions may not be good candidates for this treatment.


A thyroidectomy is where one or both of the thyroid glands are surgically removed. For most cats, this can permanently cure hyperthyroidism with no long-term treatment required.

Surgery may not be a suitable option for all cats, however. Some cats aren’t able to undergo anaesthesia, and surgery won’t be effective for cats who have ectopic thyroid tissue.

If surgery is suitable for your cat, be aware that there are risks involved, as with all operations. A thyroidectomy carries the additional risk of damaging the parathyroid glands which are very close to the thyroid glands. This can cause life-threateningly low calcium levels.

Special Diet for Hyperthyroidism

In some cases, hyperthyroidism in cats can be managed by diet. In order for T4 to be produced, iodine is needed. Therefore, a strict, low-iodine diet such as Hills y/d Thyroid Care cat food can be used to manage hyperthyroidism.

Cats being treated through low-iodine diets must not have access to any other food. This means no treats, human food, or other cat foods, and in some areas, deionised water might be necessary for dietary treatment to be effective. Cats should also be kept indoors to make sure they don’t eat anything else outside, so this form of treatment is less suitable for outdoor cats.

Wrapping Up

There are several effective treatments available for cats with hyperthyroidism, and the prognosis is very good. Many cats continue to live long, healthy lives after diagnosis. However, treatment can be expensive, so it’s a good idea to get your cat insured when they are younger so that you’re covered for future conditions like hyperthyroidism. As soon as you spot any of the symptoms of hyperthyroidism in your cat, take them to see a vet so that it can be dealt with quickly.

This blog was checked by Karin Volker, MRCVS

Biography of Animed vet, Karin Volker, MRCVS
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