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Treating Feline Hyperthyroidism with Medication

Methimazole, commonly referred to as Tapazole, is the most common medication used to treat feline hyperthyroidism. Your cat will need to take this oral antithyroid medication for the rest of his/her life. It works to inhibit the thyroid hormone from being produced at the thyroid gland. Although this seems like a simple and effective solution, the disadvantages far outweigh the benefits.


  • Side effects in 15-20% of cats treated
  • Such as: vomiting, lethargy & loss of appetite
  • Can also cause blood clotting & cell abnormalities
  • Administration of medicine is often difficult
  • Will not reduce the tumor on the thyroid
  • Required for the life of the cat

Alternative: Radioactive Iodine I-131 Treatment

Thankfully, there is a more effective treatment for feline hyperthyroidism: Radioactive Iodine I-131 treatment. The benefits of this treatment method are as follows:

  • Thyroid function back to normal, usually within a month
  • Doesn’t damage other tissue or organs, including parathyroid glands
  • No harmful side effects
  • No anesthesia required
  • No daily medication
  • Cost effective

More questions about feline hyperthyroidism and treatment? Learn more about the common treatments for feline hyperthyroidism.