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Hyperthyroidism In Your Cat

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thyroid-152x300Your cat’s thyroid glands regulate the speed at which your cat’s body metabolism works. They do this by producing a hormone called thyroxine and sending this hormone to every cell in the body through the bloodstream. When your cat produces too much thyroxine and its metabolic rate soars, the cat has become hyperthyroid.

Hyperthyroidism is the most common hormone abnormality in cats, typically occurring in older cats. In the cat, the thyroid is a pair of glands that are located on the underside of the neck along the windpipe (trachea).

Signs of Hyperthyroidism:      

  • Weight loss
  • Increased appetite
  • Increased activity and restlessness
  • Poor or unkempt hair coat
  • Fast heart rate
  • Increased drinking and urination
  • Vomiting
  • Diarrhea
  • Panting or difficulty breathing
  • Weakness & listlessness
  • Low grade fever
  • Lumps & nodules in the neck where thyroid glands are

Please call your veterinarian immediately if you notice these or any other strange symptoms in your cat. If your veterinarian suspects that your cat might have hyperthyroidism, a T4 bloodtest will be ordered. The diagnosis is made if the results are markedly higher than normal levels.


  • Medication – Methimazole (tapazol) is the drug used to treat hyperthyroidism. This is supplied in pill form but can be compounded into a transdermal gel that is applied to the cat’s ear. Treatment may be made 1-2 times daily, while the effectiveness of the treatment is monitored with periodic T4 bloodtests, and medication dosages adjusted as needed.
  • Radioiodine Therapy – This procedure is only performed at specialized veterinary centers because it involves the handling of radioactive materials. A single injection of radioactive Iodine-131 is given and the cat will need to stay at the hospital facility until the radiation that is released has subsided (usually 1-2 weeks).
  • Surgery – Surgical removal of the thyroid gland tissue is no longer advised due to the post-surgical problems that can arise.
  • Food – Hills™ Prescription Diets™ has developed a new food to treat hyperthyroidism called Y/D – Feline Thyroid Health. Y/D limits the cat’s iodine intake, which controls thyroid hormone production. This diet has been proven to restore the cat’s body condition, skin and coat in just three weeks. The Y/D diet is to be fed exclusively; no treats or other foods allowed. Thyroid levels will be monitored with periodic T4 bloodtests.