Feline hyperthyroidism is caused by an unregulated overproduction of thyroid hormone by the thyroid glands, which is usually related to a benign enlargement (growth or tumor) of one or both thyroid lobes. The cause of the enlargement is unknown.

The thyroid gland acts as the thermostat for the metabolic rate of the body, controlling how fast or slow the body functions. Hyperthyroidism can have effects on multiple organ systems, since the increased thyroid hormone levels increase the cat’s metabolic rate.

Although this disease is usually diagnosed in older cats (at least 9 years of age), it has been diagnosed in cats as young as 6 years of age. There is no recognized breed or sex predilection for this disease.

Diagnosis and Treatment Notes:

  • Hyperthyroidism is diagnosed through blood tests, specifically a thyroid level (T4).
  • Treatment is directed at controlling excessive secretion of thyroid hormones and depends on the severity of the disease, your individual pet, and your veterinarian. Treatment options include radioactive iodine therapy, surgical removal of the abnormal thyroid lobes or medical therapy with Tapazole® (methimazole) and beta-adrenergic blockers (such as atenolol) to reduce some of the symptoms of hyperthyroidism. Discuss treatment details when your pet is diagnosed with this condition.


What to Watch for*:

  • Weight loss with an increased appetite
  • Restlessness
  • Irritability
  • Increased activity levels
  • Lethargy


*Please notify us if you notice any of the above signs or if you have any questions!