Treatment options for hyperthyroid cats

If your vet just told you your cat has an overactive thyroid, you’re probably a bit relieved that it is a treatable disease! Treatment options vary, and there’s bound to be one that works for you and your cat!

Methimazole / Tapazole

This is the original treatment. It comes in pill form (small pills too!), and if your cat eats them in pill pockets or canned food, then you’re good to go! If your cat is not falling for that trick (puh-lease!) many compounding pharmacies can make a flavored liquid (tuna, chicken, etc). Still not happening? These same miracle workers also can concoct a transdermal medication. This is a cream you rub into the skin on your cat’s ear, and it gets absorbed into the bloodstream. Pretty amazing! Regardless of how you get the medication into (or onto) your cat, it can have side effects, like vomiting or decreased appetite. There are also potential side effects of white blood cells that your veterinarian will want to check for. This medication lowers the thyroid level, and will need to be given for life. It tends to be relatively affordable, thankfully. Your veterinarian will need to recheck your cat’s blood usually about 4 weeks after starting, and then every 6 months…or more often if there are abnormalities or dosage changes.

Radioactive I-131

Yes, we want to radiate your cat! This is actually a really cool treatment that offers a permanent fix (in 97% of cats). It does involve your cat spending several days in a hospital, so that’s a bummer. But if you have a cat who is just impossible to medicate, or is not very old, this is a great option. It typically runs a little over $1,000 and involves your cat being gone for 5-10 days. A radioactive Iodine is given that the thyroid gland immediately sucks up. All the hyperactive cells in the thyroid gland can’t get enough Iodine, because they are trying to produce as much thyroid hormone as possible (Iodine is a requirement to make thyroid). So the I-131 is a Trojan horse of sorts. It goes into the overactive cells that eagerly take it in… and kills them. The non-hyperactive cells are left alone. The reason your cat has to be in the hospital is because they can’t send home a radioactive cat, and it takes several days for the half-life of the I-131 to work its way out.

Prescription diet

Hill’s came out with a game-changing diet a couple years ago called y/d. All you have to do is feed your cat this food. The catch? It must be ONLY that food. It is devoid of Iodine, which is a key ingredient in making thyroid hormone. Without Iodine, the body cannot make extra thyroid hormone. However, there is iodine in pretty much every food. So if your cat gets even one bite of anything else, the food will not work. For single cat households, this is a great option. With multiple cats it can be tricky. I do have owners who leave the y/d for all the cats to eat, and feed the other, non-hyperthyroid cats a sneaky meal of canned food every day so they can maintain their thyroid levels. This works when all the cats in the house or older, but does not work for kittens. The food would need to be fed for life to remain effective.


Another permanent fix is to surgically remove the over-active thyroid gland. This is a rather straightforward surgery, but there are some potential life-threatening complications if not performed correctly. If your vet does not do this surgery often, then visit a specialist to have it done. If your veterinarian enjoys doing this procedure often, then let her! Prior to I-131, surgery was the only permanent solution. It has fallen out of favor lately, due to the I-131 option. However, with thyroidectomy surgery, your cat is only in the hospital for one day, not weeks like the radioactive treatment.


Posted in Feline specific, Senior pets.

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