Radioactive Iodine Therapy FAQs

For The Treatment of Hyperthyroidism in Cats

My veterinarian has diagnosed my cat with hyperthyroidism and recommends Radioactive Iodine (I131) Therapy for the Treatment of Hyperthyroidism in Cats.

Now what?

Sample DesDr. Carney needs to see you and your cat before treatment with Iodine 131 for Hyperthyroidism so that she can examine your cat and obtain all the information needed to calculate what dose of I131 your cat needs to be given.  The Iodine 131 has to be made by a radio-pharmacy in Boise and delivered to Four Rivers Veterinary Clinic on the morning of the treatment. If your dose was preordered without Dr. Carney first seeing your pet and we did not treat your cat, there would be a charge to you for this dose.  Remember Dr. Carney sees patients out of West Vet Emergency Clinic in Boise on most Tuesdays and Wednesdays, so that you do not have to travel to Ontario Oregon for this pretreatment visit. Be sure your regular veterinarian sends all your cat’s information to Dr. Carney at either West Vet or Four Rivers so that she can be ready for your pretreatment visit. cription
Sample DesCurrently the cost of treatment for a four to seven (4 to 7) days stay is $1300 to $1500 dollars. Other costs may vary with the examinations and follow up lab tests your cat would need after treatment.cription

After i-131 treatment your cat will have a very low amount of radiation in it’s body. Please note that this amount is about 50 times less than you would have if you were treated with I-131. It is about the same amount as you would receive flying across the country in an airplane. Because of this radiation, the Department of Radiation Safety of Oregon has several requirements for owners.

  • Your cat must ride home in a carrier.
  • For the first 2 weeks use rubber gloves when cleaning your cat’s litter box.
  • Use flushable litter so that you can dispose of your cat’s waste in the toilet, not the garbage. (For 3 to 4 weeks following treatment your cat will excrete unabsorbed I-131 and radioactive waste products in its urine and stool).
  • Pregnant women and people receiving chemotherapy should not clean the cat's litter box or medicate the cat.
  • Closely snuggle with the cat for only about an hour a day.
  • By law your cat must stay at home with you or be boarded with us for these two (2) weeks; he cannot go outdoors.
  • We recommend that you have us or your cat’s regular veterinarian re-examine your cat and run blood work at 4 and 12 weeks post treatment.


If lots of hyperactive thyroid cells die and release stored thyroxin, the cat’s already fast running systems will run faster. A slight risk exists that the cat will have a significant abnormal heart rhythm or increase in blood pressure for 2 to 3 days following the I-131 injection. Your cat will be closely monitored to prevent serious reactions. Occasionally a cat has a sore throat or hoarse voice for 7 to 10 days. In rare instances, the iodine will kill all the thyroid cells and the cat will need oral thyroid supplementation.


Your primary care veterinarian needs to speak with Dr. Hazel Carney about your cat’s condition and will send copies of your cat’s records to her at Four Rivers Veterinary Clinic. After she has spoken with your veterinarian, you may set up an initial consultation appointment with Dr. Carney either at Four Rivers Veterinary Clinic or at West Vet Emergency and Specialty Center where she will perform s thorough physical examination on your cat. This will allow her to determine if any other testing is needed before treatment and allow her to explain the treatment more completely. Once all of your questions about this disease and treatment are answered, she can schedule your cat’s treatment date. Because of Idaho state regulations the therapy takes place here in Oregon at Four Rivers Veterinary Clinic.

The morning of the treatment you will drop your pet off at Four Rivers Veterinary Clinic. You may bring something that smells like home and your cat’s regular diet. The clothing item must be disposable. Due to safety guidelines, the item cannot go back home after treatment.

The I-131 injection is given under the skin and then your cat will stay for an average of four to seven (4 to 7) days. Oregon state law requires a minimum of four (4) days stay. While staying at Four Rivers Veterinary Clinic, your cat is monitored closely by Dr. Carney, Dr. Robinson and technicians. Your cat’s radiation levels and other vital signs are monitored several times a day. The radiation ward is upstairs at Four Rivers Veterinary Clinic, away from any dogs and is a quiet place where most cats are very relaxed.

We provide plenty of warm, cozy bedding and have music available. We have had owners bring special recording of their own voices for us to play during their cat’s stay. Please note that state law does not allow owners to visit during the stay but we provide daily updates on your cat’s progress, and we give as much TLC as we can.

Radioactive iodine therapy is considered the state of the art treatment for humans and cats. Its many benefits include the fact that it cures 98% of all cases with a single treatment, it requires no anesthesia, and avoids surgery. It is safe for both old and young cats and avoids the need for your cat to take life long drugs.

A cat’s body uses iodine to made the thyroid hormone thyroxin. After injecting your cat with I-131, hyperactive thyroid cells absorb the I-131 and this in turn kilss the abnormal thyroid cells. As the abnormal cells die, excess hormone production stops and your cat’s thyroid level will return to normal.