Radioactive Iodine Therapy for Hyperthyroid Cats

Portland Veterinary Emergency and Specialty Care is proud to offer radioactive iodine therapy for hyperthyroid cats. Dr. Gail Mason is leading our team in these treatments. 

Radioactive I-131 is a highly effective and well-tolerated treatment for hyperthyroidism, a common medical condition affecting older cats that results in excessive thyroid hormone. 

In most cases, the condition results from a benign tumor of the thyroid gland, which causes excess thyroid hormone secretion.

Excessive hormone secretion causes accelerations of bodily processes and clinical signs that are apparent to owners. Such signs include increased appetite, weight loss, rapid heart rate, muscle weakness, restlessness, vocalization, vomiting, diarrhea, increased thirst/urination, and heat intolerance.

Over time, the accelerated metabolism leads to deleterious effects on the cat’s internal organs. Resultant heart disease, kidney disease, and/or intestinal disease can ultimately lead to death. Fortunately, the disease is very familiar to veterinarians and is most often easily and rapidly diagnosed by measuring the level of thyroid hormone (T4) in the bloodstream.

The ideal goal of 1-131 therapy is to restore normal thyroid function with a single dose of radiation without permanently damaging normal thyroid tissue. Most hyperthyroid cats treated with 1-131 are cured by a single injection — No surgery! No anesthesia! No medication!

Successful treatment results in normal thyroid hormone levels within 2 weeks of treatment in 70-8O% of cats. Over 90% of treated cats reach normal hormone levels within 3 months post-treatment. Cats often feel better within days of treatment and most owners can expect gradual and steady health recovery within 2 months. If you think radioactive iodine therapy for hyperthyroid cats could be a help to your pet, please talk to your family veterinarian about a referral.


These diagnostic tests are required before your cat can be admitted for radioactive iodine therapy. We recommend that these tests be completed at your regular veterinarian’s office one to two weeks before your radioactive iodine consultation. If these tests have not been completed, they can be completed at the time of your radioactive iodine therapy consultation.

All cats must have up-to-date vaccinations before being brought in for treatment. 

Lab Work

  • CBC, Chemistry
  • SDMA
  • Urinalysis
  • Thyroid level

Whole-Body Radiograph  

  • Radiograph(s) can be emailed to PVESC if digital, or brought with you to your appointment

Copies of all pertinent medical records and test results regarding your cat’s treatment will be forwarded to your primary care veterinarian. We recommend a recheck examination, thyroid (T4) level, and kidney (renal) profile with your veterinarian 2-3 months after I-131 treatment. Please have the results forwarded to PVESC.