Cat Radioiodine Treatment for Hyperthyroidism

Radioiodine therapy is the gold-standard curative treatment for feline hyperthyroidism. Understanding the procedure, welfare considerations, and aftercare helps owners make informed treatment decisions.

Key Facts

Radioiodine (I-131) treatment achieves complete cure in over 95% of treated hyperthyroid cats
The treatment involves a single subcutaneous injection of radioactive iodine that selectively destroys abnormal thyroid tissue
Treated cats require hospitalisation in a licensed facility until radiation levels fall to legally permissible levels — typically 3-7 days
The treatment causes no pain beyond the injection and has fewer side effects than long-term methimazole administration
Approximately 2-5% of cats become hypothyroid after treatment and require lifelong thyroid supplementation
Radioiodine is more cost-effective than lifetime medication for most cats with a long expected survival

Welfare Considerations

The primary welfare consideration in radioiodine treatment is the mandatory isolation period, which can be stressful for cats that are already unwell and separated from familiar environments and owners. However, this short period of stress is far outweighed by the welfare benefit of permanent cure compared to years of daily medication, repeated blood tests, and continued hormonal imbalance. For most hyperthyroid cats with good kidney reserve, radioiodine offers the best long-term welfare outcome.

What You Can Do

Ask your vet about radioiodine as a treatment option when hyperthyroidism is first diagnosed
Complete a methimazole trial first to assess kidney function before committing to permanent treatment
Prepare your cat for the isolation period with familiar bedding and items from home to reduce stress
Understand the radiation safety precautions required at home for 2-3 weeks after discharge
Schedule kidney function tests 4-6 weeks after radioiodine to assess post-treatment renal status
Discuss cost-benefit analysis with your vet — radioiodine is often more cost-effective long-term than medication