Feline hyperthyroidism became one of the most common conditions in older cats in the 20th century, with radioactive iodine treatment now available as a curative option that improves welfare significantly over lifelong medication.
Hyperthyroidism causes significant welfare suffering through the hypermetabolic state it creates, including restlessness, muscle wasting, and cardiac complications. Daily medication controls the condition but requires stressful daily handling that some cats find aversive. Radioactive iodine treatment, while requiring specialist referral and a brief period of isolation for radiation safety, provides a permanent cure that eliminates the ongoing welfare costs of daily medication and disease progression. The welfare improvement from curative treatment is substantial for cats and reduces long-term stress on both cat and owner.