Hyperthyroidism & Liver Function in Cats

"Taking a pill every day was really a drag, plus it hurt my liver."
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If your kitty's diagnosed with hyperthyroidism, it's probably affecting every organ in his body to some degree. While the disease can affect his liver, it's more likely to directly trouble his kidneys, heart and respiratory system. One common treatment for the disease causes liver problems in some felines.


If your cat is age 10 or older and continuously loses weight even though he's always hungry, suspect hyperthyroidism. The thyroid glands on his neck regulate much of his metabolism. If they produce too much thyroid hormone, resulting in hyperthyroidism, it throws his whole system a curve. A benign tumor on the glands is the usual cause of hyperthyroidism. Other symptoms include excessive drinking and peeing, hyperactivity, personality changes -- not for the better -- and breathing troubles. Your vet diagnoses the condition by testing the thyroid levels in Buffy's blood.

Hyperthyroidism and the Liver

A study conducted by the University of Pennsylvania's Mathew J. Ryan Veterinary Teaching Hospital and published in 2007 evaluated "serum markers for liver function and damage, and ultrasonographic changes in cats with hyperthyroidism and with high liver enzymes," to determine if these issues resolved after cats received radioactive iodine therapy. The study matched 19 hyperthyroid cats, 15 of which had high serum liver enzymes, with four healthy control felines. While the study concluded that cats with high liver enzymes returned to normal after radioactive iodine therapy, it also concluded that extensive examination for liver disease in cats diagnosed with hyperthyroidism wasn't necessary.


If your vet prescribes methimazole, marketed under the brand names Felimazole or Tapazole, to treat Buffy's hyperthyroidism, there's a small chance that the drug can affect liver function. You'll have to pill your cat once or twice a day for the rest of his life, or apply the transdermal gel form of the medication to his inner ear. While most cats tolerate methimazole well, about 15 percent develop issues within two months of starting therapy. Approximately 2 percent experience liver failure, according to VeterinaryPartner.com. Those cats must immediately stop receiving the medication.


If your cat falls into that tiny percentage developing liver failure with methimazole, you have a couple of options. Your vet could perform a thyroidectomy, or surgical removal of the thyroid glands. This usually cures hyperthyroidism, while methimazole only treats it. However, since most hyperthyroid felines are elderly, surgery isn't always a possibility. The treatment of choice is radioactive iodine therapy, which also offers a cure and is easy on the cat. It might not be so easy on you, because only certain veterinary facilities offer the procedure. It consists of a single radioactive iodine injection, but Buffy must stay at the facility for several days or weeks until his radioactivity levels drop enough for him to go home. You won't be able to visit him while he's at the facility, because of exposure danger.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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