Treating Hyperthyroidism in Cats

Treating Hyperthyroidism in Cats
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vet verified PetCareRx Staff Veterinarian DVM

There are three different treatment options for cats facing hyperthyroidism: surgery, medication, and radioactive-iodine therapy. Learn more here.

Treatment for hyperthyroidism may involve one of three options, depending on the type of tumor on the thyroid. The first option your veterinarian may recommend is medication, while surgery and radioactive-iodine therapy may be considered based on whether the medication is effective. When choosing the best route of treatment, your veterinarian must take into account the general health of the cat, and more specifically, health of the heart and kidneys. These organs can be adversely affected by some treatments.


Medications such as methimazole are often prescribed to help fight feline hyperthyroidism. There are many benefits to choosing methimazole, one being the fact that it is usually reasonably priced; however, it is not right in every case. Methimazole can be given orally, or absorbed from a paste in the ear, but it does require administration twice a day or more for the rest of the pet’s life. It works by controlling the production and release of the T4 and T3 hormones, effectively balancing the system. There are mild side effects associated with methimazole, such as vomiting and lethargy.


Surgery, in some cases, is a cure for hyperthyroidism in cats. If the feline is healthy enough to undergo major surgery, most notably based on heart and kidney health, the full removal of the thyroid glands can be the most effective option. This option, however, comes with major risk as well. There are parathyroid glands located near the thyroid, which are essential to the balance of the blood-calcium levels. If these parathyroid glands are compromised, the animal may be worse off than prior to surgery. This option tends to be avoided in cases of cats that are very old.

Radioactive-Iodine Therapy

This type of therapy is a highly recommended option, based on a 95% success rate, and very few side effects. This procedure, however, can only be performed in specialized treatment centers, authorized to handle radioactive material. The radioactive iodine is injected into the blood stream of the cat, with no anesthesia necessary. The iodine then reaches the thyroid gland and destroys the tissue in the thyroid that is causing problems. Rarely does this ever cause an adverse effect to the healthy tissue or the parathyroid glands. After the injection, the cat must remain quarantined in the facility, with no exposure to unprotected humans, for about two weeks. By then the radioactivity of the iodine should have fallen to safe levels. This treatment can cure hyperthyroidism in cats without the threat of many negative side effects. If the first round does not cure the problem, it may be performed again.

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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