Hyperthyroidism is the most common endocrine disease in older cats. With multiple effective treatment options, most affected cats can enjoy excellent quality of life when properly managed.
Feline hyperthyroidism is an excellent example of a serious welfare problem with highly effective solutions. Untreated hyperthyroid cats experience hypermetabolism that causes muscle wasting, heart enlargement, hypertension, and progressive organ damage despite a voracious appetite — a paradox that misleads some owners into thinking their cat is healthy. With treatment, most cats return to normal thyroid function and experience years of healthy life. The welfare consideration is ensuring that all affected cats receive prompt diagnosis and appropriate treatment. Radioactive iodine, though requiring a brief quarantine period after administration, offers a one-time cure without lifelong medication. Medical management with methimazole is more accessible but requires regular monitoring and carries some risk of side effects. Selecting the right treatment requires individual assessment.