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.

Three treatment options exist: a single dose of radioactive iodine, I-131 (the treatment of choice), surgery, or life-long oral methimazole medication. Surgery’s drawbacks include general anesthesia, invasiveness, complications, and expense. Methimazole’s disadvantages include costly daily medication for life, potential side effects such as lack of appetite, vomiting, potential toxicity causing severe facial skin reaction and blood cell abnormalities, and long-term blood monitoring.

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, cats are closely monitored onsite as radioactivity levels drop off for five to seven days. Once home, cats typically return to normal within a matter of weeks. For more information about hyperthyroidism and radioactive iodine therapy see our Knowledge Center article.

Iodine therapy client checklist.