Companion Animal Welfare

Cat Hyperthyroidism: Dietary Iodine Restriction Therapy

A prescription iodine-restricted diet (Hill's y/d) offers a non-invasive treatment option for hyperthyroid cats that cannot tolerate medication or surgery.

Key Facts

Hill's Prescription Diet y/d restricts dietary iodine to below 0.2 ppm to reduce thyroid hormone production
It can normalise thyroid function within 4-8 weeks in cats fed exclusively on the diet
The diet must be the sole food source - any other food sources can negate the effect
It is most suitable for cats with no other health conditions requiring dietary management
Other concurrent conditions (e.g., CKD) may complicate the use of dietary therapy for hyperthyroidism

Welfare Considerations

Dietary therapy for hyperthyroidism offers a welfare advantage for cats who cannot tolerate twice-daily medication or anaesthesia for surgery. However, strict dietary compliance is essential and the diet must be palatable to the individual cat. Regular monitoring of thyroid levels, kidney function and weight is essential to ensure the diet is working and that unmasked kidney disease is identified early.

What You Can Do

Discuss all treatment options for your hyperthyroid cat with your veterinarian
If using dietary therapy, strictly exclude all other food sources including treats
Monitor thyroid levels and kidney function as directed after starting dietary treatment
Learn about the interactions between hyperthyroidism and kidney disease in senior cats