Any long-term side effects from radioiodine for cat hyperthyroidism?
Updated On September 23rd, 2025
Pet's info: Cat | Domestic Longhair | Female | spayed | 12 years and 11 months old | 7 lbs
Hi, my cat has just been diagnosed with Hyperthyroidism, I would like to get her the radio iodine treatment but am concerned about any long term side effects, are there any? She is an otherwise healthy girl of almost 13 years old. Thank you, Sue
2 Answers
Most Helpful Answer
Published on July 17th, 2017
Usually cats do well with the radio active iodine therapy. There is a chance for them to become hypo thyroid meeting they would need thyroid supplementation after the treatment. But generally speaking most cats do very well and no further treatment is needed. However your veterinarian will need to make sure there's no other underlying issues such as early kidney disease prior to doing the radio active iodine therapy. If they do find other issues then your cat may not be a good candidate for that treatment but other treatments such as daily medication or even surgery to remove part of her thyroid gland might be options.
1Pet Parents found this answer helpful
Related Answers from Veterinarians
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Published on September 17th, 2019
Hello. Yes, your concerns are valid, but it is amazing how well a pet can cope in these situations. It might be best to endure a few days of discomfort vs a lifetime of fighting with Patches to get a pill down her. Radioactive iodine therapy is the gold standard for treatment, but some cats have responded to diet therapy ( Hill's y/d ) while other cats have done well with transdermal methimazole ( applied to the inside of the ears ). Radioactive iodine therapy is contradicted in cats with concurrent health issues such as kidney disease or heart problems, but if Patches is otherwise healthy I would not be worried about stressing her out too much. The veterinary hospital that will perform the procedure should be very well versed in dealing with these older kitties. Never be afraid to discuss your concerns with your veterinarian as they should know Patches' health & temperament quite well. Thanks for using Petco Pet Education Center, formerly Petcoach.
1Pet Parents found this answer helpful
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