Feline hyperthyroidism is the most common endocrine disease in older cats with four treatment options — medication, radioiodine, surgery, and dietary therapy — each with distinct welfare profiles.
Untreated hyperthyroidism causes multi-system suffering: cats experience the distress of insatiable hunger despite continuous eating, restless hyperactivity, progressive muscle wasting, and cardiovascular strain. The selection of treatment option significantly affects ongoing welfare. Daily methimazole administration causes pill-aversion, vomiting in some cats, and rare serious side effects including facial scratching from drug hypersensitivity. Transdermal application reduces oral stress but has lower efficacy. Radioiodine offers the best long-term welfare outcome — a single procedure produces sustained remission without ongoing stress of medication administration, though the post-treatment isolation period requires welfare management. Dietary therapy requires complete food restriction that causes welfare problems in multi-cat households.