catsveterinary doctor

Overactive thyroid in cats (hyperthyroidism)

Cats with an overactive thyroid usually require lifelong medication.

Takes your velvet paw despite a good appetite always on away? Then it could be that sie suffers from hyperthyroidism. You can find out what you should know about hyperthyroidism in cats in our guide.

Symptoms: How does an overactive thyroid gland manifest itself in cats?

The thyroid hormones influence important cell functions. Therefore, hyperthyroidism in cats affects a variety of organs. Associated with this is a variable clinical picture (symptoms).

An overactive thyroid in cats often manifests itself in the following symptoms:

  • high blood pressure
  • Weight loss despite increased appetite
  • hair loss and the rest of the fur looks shaggy
  • Cat panting and pointing breathing problems
  • increased drinking and urination (polydipsia and polyuria)
  • increased activity and general restlessness
  • difficulty swallowing

Sometimes you may also see behavioral changes in your cat, such as sudden aggression or fear. If the disease affects the gastrointestinal tract, also occur Diarrhea or Vomit on.

Final Stage: This happens to untreated cats

If your cat with thyroid disease is not treated, it will gradually reach the end stage of the disease. The hormones have a negative effect on the heart, causing blood pressure to rise. This blood pressure then damages other organs such as the kidneys or the eyes.

Diagnosis: How can an overactive thyroid gland be detected in a cat?

In order to be able to prove an overactive thyroid gland in a cat, you can Veterinarians use various diagnostic tools after the general clinical examination:

blood test

If the veterinarian takes blood from your cat, he can then check the sample for various parameters. Hyperthyroidism in cats is often associated with an increase in liver enzymes (e.g. alanine aminotransferase or alkaline phosphatase).

Creatinine is often reduced as a result of the worsening of muscle activity in the context of hyperthyroidism.

thyroid tests

Your veterinarian can also measure the concentration of various thyroid hormones in the blood. This includes, for example, measuring serum T4 or free T4 (ft4).

With the TSH test, the veterinarian checks the communication between the pituitary gland (pituitary gland) in the brain and the thyroid gland. Your veterinarian will expect low TSH levels in sick cats, since the increased T4 associated with hyperfunction suppresses the release of TSH from the pituitary gland.


Veterinarians often use sonography (ultrasound) to rule out thyroid disease. With the help of the ultrasound device, he can assess the size, shape and location of the thyroid tissue.

Meanwhile, he can also perform an ultrasound-guided fine-needle aspiration to take a tissue sample to assess whether the tumor is benign or malignant.


If your vet has found a nodule in the thyroid gland, he can then use the thyroid scintigraphy to check the iodine metabolism of the thyroid gland. He gives your cat radioactive substances (radionuclides) that are similar to iodine.

The gamma rays emitted by this radioactive substance can then be visualized by your vet using a special camera. Your veterinarian then compares the images with the values ​​of the salivary gland in order to identify changes in the thyroid gland.


Other diagnostic tools are also helpful to check the condition of other organs. This is how your veterinarian can use a X-ray examination Assess abdominal organs such as the liver or kidneys.

Therapy: How is an overactive thyroid treated in cats?

Veterinary medicine distinguishes between reversible (reversible) and non-reversible (non-reversible) therapy.

1. The reversible treatment

The form of therapy includes a medication with antithyroid drugs. The drugs carbimazole, methimazole or thiamazole inhibit the hormone production of T4 and T3.

If you stop taking methimazole, the thyroid starts overproducing again. Therefore, it is a lifelong therapy.

It’s also important to have your cat’s thyroid levels checked regularly (about every three months). This is the only way your veterinarian can adjust the dose individually and reduce side effects if possible.

In addition to or as an alternative to other treatments, you can also use the nutrition switch your cat. The exclusive administration of iodine-reduced cat food also regulates the concentration of the increased serum T4. Your veterinarian will educate you on what dietary foods are appropriate for your cat.

Note: Choosing a suitable diet food can support your cat’s natural bodily functions. Please note, however, that diet foods can neither cure nor prevent diseases. You should also always discuss the right diet for your cat with your veterinarian. You can find special diet feeds in the zooplus online shop.

2. The non-reversible treatment

Non-reversible measures come into question when reversible steps are not (or no longer) effective.

The gold standard is the radioiodine therapy. Here, the radioactively marked iodine injected into the veins or under the skin destroys the pathologically altered glandular tissue. In most cases, a single application is sufficient.

A second possibility is this thyroidectomy. This means the surgical removal of the entire thyroid gland.

Costs: How expensive is the treatment of an overactive thyroid in cats?

Long-term drug therapy is associated with ongoing costs. So you have to reckon with around 30 euros per month for the corresponding tablets. There are also additional costs for the veterinary examinations.

The costs of surgical removal of the thyroid gland or radioiodine therapy vary between 1000 and 2000 euros.

However, factors such as your cat’s weight (used to calculate the dose of medication needed) can affect individual costs.

Causes: What triggers an overactive thyroid in cats?

Hyperthyroidism is when your cat’s thyroid secretes too much thyroid hormone. This important gland lies to the left and right of the windpipe in your cat’s throat. The best-known thyroid hormones include thyroxine (T4) and triiodothyronine (T3).

Tumor as the most common trigger

Most often, pathological changes in the thyroid tissue are responsible for hyperthyroidism in cats. These include, for example, hormone-producing tumors in one or both thyroid lobes.

The majority of cats with cancer have a benign adenoma. More rarely, cats develop an aggressive T4-producing carcinoma.

Other causes and contributing factors

However, some affected cats suffer from adenomatous hyperplasia. The tissue of the thyroid increases, so that the gland produces more hormones.

Scientists have not yet fully clarified what leads to the development of hyperthyroidism in cats. However, the following factors are suspected of increasing the risk of disease:

  • radioactive radiation
  • chemical stimuli (e.g. poisons, antiparasitics)
  • cat litter
  • Wet food with too high an iodine concentration

Prognosis: Is an overactive thyroid in cats curable?

The prognosis for an overactive thyroid in cats is generally good. Does your cat suffer from serious concomitant diseases (e.g. chronic kidney disease), but these can limit life expectancy.

If you don’t have your cat treated, you have to assume that it will gradually reach the end stage and lose vitality.

Life Expectancy: How Long Can a Hyperthyroid Cat Survive?

Since most cats with an overactive thyroid gland have a benign tumor in the thyroid gland, these animals can look forward to a normal cat life without any further restrictions after successful treatment.

Prevention: How to protect your cat from an overactive thyroid

Unfortunately, you cannot prevent the hormonal disease. However, by following these tips, you can support your cat’s overall health:

  • Feed always treat your cat in a species-appropriate manner.
  • Make sure your cat gets enough exercise (especially house tigers).
  • Have your four-legged friend checked regularly by a veterinarian.

You can find tips on how to ensure your cat gets enough exercise in our section Cat sport & play.


  • Hans Lutz / Barbara Kohn / Frank Forterre (eds.): Cat diseases. 6th edition, Stuttgart 2019.
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One Comment

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