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Excess thyroid hormone—generally caused by a benign thyroid tumor—leads to feline hyperthyroidism, a common disorder among older cats. Clinical signs include weight loss despite ravenous hunger, excessive drinking/urinating, restlessness and hyperactivity, vomiting, and diarrhea. Without treatment, complications can include heart disease, hypertension, and kidney disease.

Four treatment options exist: a single dose of radioactive iodine, I-131 (the treatment of choice), surgery, oral methimazole medication, and dietary therapy with Hill’s y/d diet. Surgery’s drawbacks include general anesthesia, invasiveness, complications, and expense. Methimazole’s disadvantages include costly daily life-long medication, potential side effects such as lack of appetite, vomiting, potential toxicity causing severe facial skin reaction and blood cell abnormalities, as well as long-term blood monitoring. Dietary therapy must be strictly adhered to and some cats do not like the diet.

We’ve healed more than 500 cats with I-131—a single injection beneath the skin does the trick. Since the thyroid is the only organ that uses iodine, radioactivity quickly collects there. Quick, safe, and painless, I-131 produces a cure 98 percent of the time. I-131 typically causes no clinical signs or illness. After treatment, we closely monitor cats on-site as their radioactivity levels drop off for 7 to 10 days. Once home, cats typically return to normal within a matter of weeks.

For more information about hyperthyroidism and radioactive iodine therapy click here.

Iodine therapy client checklist.

Contact Us

South Carolina Veterinary Specialists & Emergency Care


3924 Fernandina Road Columbia, SC 29210

Hospital Hours

Emergency: 24 hours
Specialty Departments: Monday-Friday: 8 am - 6 pm
Urgent Care: 1:00 PM - 11:00 PM, 7 days a week (conveniently located in the same building as our ER)