Do Cats Have to Be on Methimazole Forever?

"I was radioactive for a while, now I'm just more active."
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If your cat suffers from hyperthyroidism, your vet might prescribe methimazole to treat his condition. Kitty might have to stay on the drug for the rest of his life, but medication for hyperthyroidism is no longer the only game in town for treatment. Alternative methods can actually cure hyperthyroidism.


If your cat is middle-aged or older, be on the lookout for signs of feline hyperthyroidism. It's a fairly common condition in cats, when the thyroid glands produce too much thyroid hormone. Your cat has two thyroid glands in his neck, which regulate his metabolism. Hyperthyroidism generally occurs because of a benign tumor on a gland, although malignancy is possible.

Symptoms of hyperthyroidism include weight loss even though your cat's constantly hungry, poor coat, rapid heartbeat, increased drinking and urination, lethargy, crankiness, high blood pressure, breathing problems and vomiting. Untreated hyperthyroidism can affect his heart, kidneys and liver. Your vet makes a diagnosis by checking thyroid levels in Kitty's blood, among other tests. She can advise you on treatment options for your cat.


Marketed under the name Tapazole, methimazole is used to block production of the T3 and T4 thyroid hormone. You'll need to give your cat pills two or more times daily for the rest of his life, although a transdermal version, a gel you place in his ear, is also available. He'll require regular veterinary visits to monitor the thyroid levels in his bloodstream, because the drug could cause hypothyroidism, or insufficient amount of thyroid hormone. Any side effects generally occur within the first three months of administration, often going away on their own. Kitty might become depressed, or experience vomiting and diarrhea. One rare side effect involves self-mutilation -- cats continually scratch their faces and necks.


If your cat is healthy enough to undergo anesthesia, surgical removal of the affected tissue in the thyroid gland often solves the problem. However, even removal of the thyroid glands won't cure certain cats. In some cats, thyroid cells have moved to other locations in the body, generally the chest cavity.

Radioactive Iodine Therapy

Radioactive iodine therapy is now the treatment of choice for hyperthyroid cats. While it's expensive and only available at certain veterinary facilities, it offers an excellent chance at a cure. The actual treatment is no more complicated than giving a cat a shot containing radioactive iodine, which kills abnormal thyroid cells. However, because it is radioactive, Kitty must stay in the hospital for a number of days until his radiation levels drop enough for him to return home. You can't visit him during that period. You must take precautions for a week after he is home. The veterinary facility will inform you about proper disposal of litter while your cat might still emit low amounts of radiation. According to the North Carolina State University College of Veterinary Medicine, that one injection cures 95 percent of cats.

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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