Methimazole

Methimazole for cats is the same as the drug used to treat humans with hyperthyroid disease. This is the same reason that veterinarians prescribe methimazole for their feline patients. Hyperthyroid disease is a common ailment of older cats. You can administer cat medication for hyperthyroid disease orally or topically. Methimazole is now the preferred course of treatment for hyperthyroid disease by most veterinarians because of its low incidence of side effects. There are a few side effects that you should be aware of, however.

The common side effects include:

Loss of Appetite
Methimazole pills are very bitter in taste. The bitter taste may lead cats to quit eating food. In most cases you can avoid the loss of appetite by disguising the pill in food to minimize the poor taste.

Vomiting
As with many medications, vomiting is often a side effect of methimazole when used to treat cat hyperthyroid disease. This is often due to the taste of the pill. Disguising the pill in food can help your cat avoid this side effect.

Depression
Methimazole treatment for cat thyroid issues can cause depression in some cats. This is a side effect you will have to watch for. If this side effect develops then you will need to have your veterinarian adjust your cat’s medication.

Disorders of the Blood
Approximately 15% of cats treated with methimazole for overactive cat hormones of the thyroid will develop some from of blood disorder. The most common is leucopenia, which is a low white blood cell count. Low white blood cell counts impact the cat’s immune system and leave them prone to other diseases.

Autoimmune Disease
Most cats treated for hyperthyroid disease with methimazole for six months or longer will develop an autoimmune disease. This happens in about 50% of cats.

Excessive Scratching is a Rare Side Effect
Some cats will self mutilate their neck and face because the methimazole will cause excessive itching. This will develop in the first two weeks if it is going to develop in your cat.

Information on this medication quoted from vetinfo.com