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Feline Hyperthyroidism Information

feline hyperthyroidism info

Feline Hyperthyroidism: The Facts

Hyperthyroidism in cats is caused by excessive production of circulating thyroid hormones. Thyroid hormones regulate the body's metabolic rate and affect all tissues and every system in a cat's body.

  • It was first diagnosed in 1979.
  • It is caused by a benign tumor/adenoma.
  • It is a disease of older cats.
  • It is more common in females.
  • It is less likely to affect Siamese cats and Himalayans.
  • It is very treatable & has a good prognosis if caught early!

Common Symptoms

  • Enlarged, palpable thyroid gland
  • High blood pressure
  • Increased appetite
  • Increased body temperature
  • Increased heart rate, thirst and urination
  • Poor appearance
  • Vomiting
  • Weight loss

More information on common symptoms of feline hyperthyroidism.

Testing & Causes

A diagnostic blood testing for Total T4 levels will determine whether a cat has hyperthyroidism or not. However, about 6% of effected cats will show normal T4 levels. Elevated liver enzymes are common and can help with the diagnosis of this condition.

Causes of Feline Hyperthyroidism

Environmental factors appear to be the major cause of cats developing hyperthyroidism. These include:

  • Exposure to secondhand cigarette smoke
  • Exposure to fire-retardant chemicals called PBDEs
  • Exposure to PBDEs in fabrics and electronics
  • Feeding canned cat food (may contain too much Iodine and PBDEs)

Treatment Options for Your Cat's Thyroid

At present, there are three main feline hyperthyroidism treatment options. They are:


  • Daily lifelong treatment with pills
  • Not a cure
  • Side effects
  • Potentially toxic
  • Blood levels must be monitored


  • Very risky as cats are in poor condition
  • Complications are possible
  • Requires skilled and experienced surgeon
  • Thyroid hormone therapy required for life

Radioactive Iodine ( I-131 ) Therapy

  • No anesthesia or surgery necessary
  • No medication necessary
  • One injection cures the condition
  • Thyroid supplementation rarely needed
  • Well-tolerated

For questions, please contact us at (866) 467-8228 or email us.