Hyperthyroidism is a very common disease of the middle aged to older cat.  A tumor (which is almost always non-cancerous) on the thyroid gland starts producing too much thyroid hormone.  Symptoms are usually weight loss in spite of a great appetite, and vomiting.  Other signs you might see are diarrhea, a dull and flaky hair coat, and personality changes. Hyperthyroidism often can cause heart disease and high blood pressure.  This disease usually can be easily diagnosed with a blood test.

 There are three basic methods of treatment: An oral medication called methimazole (Tapazole); radioactive iodine treatment; or surgery. For most cats the oral medication works well. 

The disease of hyperthyroidism can actually help the kidneys, and can sometimes mask underlying kidney disease.  If the cat has both kidney disease and hyperthyroidism, it is not a candidate for radioactive iodine and the dose of Tapazole may need to be adjusted.  Kidney function must be monitored when a cat is being treated for hyperthyroidism.