Side Effects of Methimazole for Cats

Methimazole, also known as Tapazole, is a medication commonly prescribed to cats with hyperthyroidism, a condition in which the thyroid gland produces too much thyroid hormone. This medication works by inhibiting the production of thyroid hormone, helping to regulate the levels in the body. However, as with any medication, there are potential side effects that may occur.

One common side effect of methimazole is vomiting. This can occur in up to 10% of cats taking the medication, and may be accompanied by loss of appetite and weight loss. In some cases, the medication may need to be adjusted or discontinued if the vomiting becomes severe or persistent.

Another potential side effect is skin irritation or itching at the site of application. This is more likely to occur if the medication is applied topically, rather than given orally. If this occurs, it is important to speak with your veterinarian about alternative routes of administration or adjusting the dosage.

Some cats may also experience a decrease in white blood cell count while taking methimazole. This is a rare side effect, but it is important to monitor your cat’s health closely and report any signs of infection, such as fever or lethargy, to your veterinarian.

In rare cases, methimazole may also cause liver or kidney damage. This is more likely to occur in older cats or those with pre-existing liver or kidney disease. Your veterinarian may recommend regular blood tests to monitor liver and kidney function while your cat is taking the medication.

These side effects are not always present, and many cats tolerate methimazole well without experiencing any adverse effects. However, it is essential to discuss any concerns or questions about the medication with your veterinarian and to follow their instructions for administering the medication.

In conclusion, methimazole is a commonly prescribed medication for cats with hyperthyroidism, but it can have potential side effects such as vomiting, skin irritation, decreased white blood cell count, liver or kidney damage and others. It’s important to closely monitor your cat’s health while taking methimazole and discuss any concerns with your veterinarian. With proper monitoring and care, most cats can tolerate methimazole well and experience a reduction in symptoms of hyperthyroidism.


Hannah Elizabeth is an English animal behavior author, having written for several online publications. With a degree in Animal Behaviour and over a decade of practical animal husbandry experience, Hannah's articles cover everything from pet care to wildlife conservation. When she isn't creating content for blog posts, Hannah enjoys long walks with her Rottweiler cross Senna, reading fantasy novels and breeding aquarium shrimp.

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