Radioactive Iodine I-131 I-CAT Feline Thyroid Treatment Centers

Radioactive iodine I-131

Radioactive iodine (I-131) is an isotope that has been used for the treatment of hyperthyroidism in both humans and felines for over 50 years and over 20 years, respectively. It is considered the ideal treatment for hyperthyroidism. The iodine is given by a subcutaneous injection in cats, and over a short period of time, destroys the abnormal hyperplastic tissue and makes the patient euthyroid (normal thyroid levels).


Treatment with I-131 is safe and effective. It is one injection under the skin, much like a routine vaccine. The I-131 is absorbed quickly into the blood stream and the diseased thyroid tissue. Once in the thyroid gland it destroys the overactive portions of the gland. The radiation is released through the urine, the feces and normal decay.
A short stay (24-72 hours) in the I-CAT facility is required by law until the level of radiation is acceptable.

Post treatment precautions

Although radioactive iodine is safe to treat hyperthyroidism, because it contains radioactivity, there are precautions that must be taken after therapy. Because the radioactivity is primarily excreted through the urine, feces and normal decay of the iodine, our main concern is the litter box. We recommend a clumpable, flushable litter and scooping the box at least once a day and flushing the clumps down the toilet. This procedure only needs to be done for the two week period post therapy.
Other precautions over the next two week period include: keeping your pet indoors, limiting contact with your pet (avoiding sleeping with your cat), washing your hands after extensive contact with your cat, food bowls and litter box. It is very important that anyone under 18 years of age or anyone pregnant or trying to get pregnant not be involved in the care of your cat.
After two weeks you can return to the normal care of your cat.


Radioiodine I-131 effectively cures hyperthyroidism 97% of the time with only one injection. Of those cases with persisting problems a second injection is often effective.


Possible but uncommon complications include renal insufficiency, hypothyroidism, sore throat or dysphagia .