Radioactive Iodine

What is hyperthyroidism?

The thyroid glands, are a pair of glands located in the lower half of the neck. These glands control the bodies metabolic rate (the speed at which the body functions). As cats get older they commonly develop a disease called hyperthyroidism. This is a condition caused by the development of a small benign tumour in the thyroid gland(s) which causes over production of thyroid hormone. This causes the bodies metabolism to speed up. In the long term this can cause excess wear and tear, particularly on muscle tissue, including the heart.

The following signs are common in hyperthyroidism:

  • Increased appetite
  • Weight loss
  • Increased vocalisation
  • Initially increased, then decreased, activity levels
  • Less commonly vomiting, increased drinking, and poor hair coat
  • On examination a heart murmur is often detected with an increased heart rate
  • The thyroid gland(s) may be enlarged

Uncontrolled thyroid disease can lead to life threatening heart disease and hypertension (high blood pressure).


There are several different treatments for hyperthyroidism available, but it is generally accepted that the definitive treatment for hyperthyroidism in cats involves using radio-active iodine. This very selectively affects the abnormal thyroid tissue having little effect on the rest of the body.

Most cats (over 90%) are cured from a single treatment. There is no need for surgery and no need for life long medication which is often a challenge to owners and stressful for the cats.

The radio-active treatment is a capsule containing I131 (radio-active iodine) which is given by mouth, and is very safe for your cat.

Your cat will then need to be hospitalized for about 1 week after the treatment, after which they can go home, and require little after care.

The Hills Veterinary Centre is one of only two Veterinary facilities in South Australia licensed to carry out these treatments.

Prior to the treatment various tests need to be performed to ensure your cat is a suitable candidate for the treatment.

If you think your cat would benefit from I131 treatment please ring the clinic to arrange a consultation with one of the vets.