Thyroid medicine for cats

Written by missy zane
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Hyperthyroidism is all too common in older cats. In fact, some veterinarians estimate that 20 per cent of cats over age eight have hyperthyroidism. Symptoms can include a ravenous appetite without weight gain, increased drinking and urination, howling or increased vocalisation, hyperactivity or increased energy, and vomiting. However, you can manage the disease with medication.

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Methimazole (Tapazole or Felimazole)

Methimazole must be given twice a day. Side effects can include scratching the face around the ears, lethargy, loss of appetite and vomiting. A small number of cats experience liver toxicity from methimazole. The drug can also cause changes in the bone marrow.


Carbimazole is converted to methimazole in the body and is less likely to cause side effects. It, too, must be given twice a day. Although Carbimazole is not available commercially in the United States, it is available from compounding pharmacies.

Alternatives to Pills

Your cat's thyroid medicine can be compounded into chicken- or tuna-flavoured liquid that tastes good and is easy to mix into food. It can also be made into soft, moist treats or a gel to rub into the hairless side of ear tips.


A single injection of radio iodine can cure your cat's hyperthyroidism. Ask your veterinarian about treatment facilities in your area or search online (see Resources). Your cat will have to board at the facility for several days until the radiation excreted through its waste has reached a safe level. Note that some cats develop hypothyroidism after receiving a radio iodine injection.

Iopanoic Acid

Iopanoic acid has been found to be an effective alternative to methimazole and carbimazole for cats who have mild to moderate thyroid disease. It's available only through compounding pharmacies.

Supplements, Herbs and Homeopathy

Some cats with mild thyroid disease do well on supplements, herbs or homeopathic remedies. These treatments need to be customised for the cat. Consult an integrative (holistic) veterinarian for help.

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