Hyperthyroidism is a multi-system disorder in cats caused by an increase in circulating concentrations of the thyroid hormones. The excessive levels of hormones affect multiple systems in the body and cause a range of clinical signs. It is the most common feline endocrine disorder worldwide and is estimated that over 10% of all senior cats will develop the disorder.



Common clinical signs include:

  • Weight loss
  • Polyphagia (excessive appetite)
  • Tachycardia (fast heart rate)
  • Cardiac murmur
  • Polyuria/Polydipsia (excessive urination and drinking)
  • Hyperactivity/restlessness
  • Vomiting
  • Diarrhoea
  • Palpable goitre (enlarged thyroid)


Over 95% of affected cats have benign enlargement of the thyroid gland, affecting either both lobes (70% cases) or one lobe (30% cases) of the gland.

It is not known what causes enlargement of the gland. Medication is available to lower the levels of thyroid hormone which resolves the clinical signs.