My 16 year old cat has been on methimazole for hyper thyroidism. She currently takes 3.75 mg/day. She has been taking it for about 9 months and her dosage started at 2.5 mg/day. Our vet suggests continuing with this therapy indefinitely, but I see s
I-131 (radioactive iodine) is a fantastic option if your cat's T4 (thyroid hormone) and kidney values on bloodwork have remained stable while she's been taking methimazole. In fact, it's considered the gold standard treatment modality in cats that are considered good candidates. There are some cats that have existing kidney disease "unmasked" once treatment for hyperthyroidism begins, so these cats are not considered good candidates for I-131 therapy.
Hyperthyroidism is a condition that requires lifelong management, so your vet is correct in stating that treatment should continue indefinitely. However, you're correct in that you may have another good option. Methimazole is not advantageous over I-131. If anything, it has more potential side effects than I-131, but we use it since the good far outweighs the bad for the vast majority of cases. Few specialty hospitals actually administer I-131, but if you have one in your area, it is absolutely worth scheduling a consultation to help det
Updated on September 24th, 2025