Radioactive iodine treatment is the gold standard for feline hyperthyroidism, providing permanent cure in over 95% of cases with minimal procedural stress.
Radioactive iodine provides the best long-term welfare outcome for hyperthyroid cats of the four available treatment options, eliminating hyperthyroidism permanently without ongoing medication. The primary welfare consideration is the mandatory post-treatment isolation period required while radioactive iodine diminishes in bodily secretions — this hospitalization can be stressful for cats who are distressed by hospital environments. Welfare mitigation strategies including enriched hospital environments, familiar bedding and toys, and regular gentle staff interaction reduce isolation stress. For cats that tolerate hospitalization reasonably, I-131 provides permanent cure without daily medication, repeat procedures, or ongoing monitoring of liver function required by medical management. Pre-treatment kidney assessment is important as normalizing thyroid function may unmask underlying renal disease.