Hyperthyroidism is the most common endocrine disorder in older cats, causing weight loss, anxiety, and organ damage. Multiple effective treatments exist, but each carries welfare implications that require careful owner and veterinary consideration.
Feline hyperthyroidism causes significant welfare impairment through its effects on metabolism, cardiovascular function, and quality of life. Affected cats often appear deceptively energetic — owners sometimes interpret the hyperactivity and increased appetite positively — but the underlying metabolic disruption is causing muscle wasting, heart stress, and hypertension. Left untreated, the disease progresses to cardiac failure and renal deterioration. Treatment selection has welfare implications: radioactive iodine (I-131) is the most effective long-term option but requires several weeks of isolation at a specialist facility, which is stressful for the cat. Daily oral medication avoids isolation but requires reliable twice-daily pilling for the remainder of the cat's life — a significant commitment for owners and a potential welfare burden for cats who resist medication. Dietary management using iodine-restricted prescription food is an option for cats who cannot receive other treatments. The discovery of concurrent CKD after treatment initiation requires careful dose adjustment to protect kidney function.