Is Radioactive Iodine the Best Treatment for Hyperthyroidism in Cats

Is Radioactive Iodine the Best Treatment for Hyperthyroidism in Cats

Health & Safety

Hyperthyroidism, or over-production of thyroid hormone, is a very common condition of older cats. Indeed, it is becoming ever more common, though the reasons for this are not clear. Hyperthyroid cats have a variety of symptoms, usually including weight loss, increased heart rate and appetite, and poor coat condition. If untreated, there is a risk of the cat developing serious and life-threatening complications. So once identified by a blood test, a vet will prescribe different hyperthyroid treatments.

Treating Hyperthyroidism

Hyperthyroidism can be treated in a number of ways...

Diet. A special low iodine diet is available, as without iodine thyroid hormones cannot be produced. But the cat cannot eat anything else, many cats will not eat the diet, and it is very difficult to manage in a multi-cat household.

Medication is often used, designed to prevent over-production of thyroid hormone. The drugs used have various names, but all rely on the same active ingredient. The cat has to take tablets for the rest of its life, but that is all that is required, apart from regular tests to check that the dose is still correct. But some cats refuse to take pills, and although the drug is sometimes given as an ear gel, this can often be difficult to administer too. Also, some cats have serious side effects from the drug used. Even if this doesn't happen immediately, the tumour causing hyperthyroidism continues to grow, so dosage will probably need to be increased over time, which could then cause problems for the cat. And recent research suggests that some of these benign tumours, if not removed, may become malignant.

Surgery. Hyperthyroidism can be cured, rather than just controlled, with surgery to remove the thyroid tumour. But this is not suitable for all hyperthyroid cats, particularly if hyperthyroidism affects both thyroid glands. Also, thee is a risk of damage to the parathyroids, which are involved in calcium metabolism. And surgery does not work in some cases, as thyroid tumours can occur in the chest, where they are very difficult to find and remove.

Radioactive Iodine. The final treatment involves using radioactive iodine. This is a complete cure, has no side effects, and works in over 95% of cases – some sources say 99%. This article will now look in more detail at this treatment and what it involves.

Radioactive Iodine Treatment for Hyperthyroidism

Basically, radio-iodine is given as an injection in the scruff of the cat's neck. The iodine is taken up by thyroid tumour tissue, but not usually by normal thyroid tissue. The tumour is killed over time, and the cat is completely cured. Cats may respond to the radio-iodine within a very short time, such as a couple of weeks, or it may take a few months. A very small proportion of cats require a second dose, usually given six months after the first if the cat is still hyperthyroid.

How Radioactive Iodine Treatment is Done?

The treatment has to be provided in specialist centres, simply because of the nature of the substance used. The cat will be radioactive for several weeks after treatment, and this could be harmful for anyone coming into contact with it. At the moment there are around ten centres in the UK providing this treatment, and cats have to be referred by their own vet. Assuming the cat is suitable, ie has no health problems which would make radioactive iodine treatment a bad idea, the cat will be admitted, given the injection, and then kept alone in a small pen. They are given food and water of course, and can usually be petted to a small extent, provided the person handling them has suitable protection from the radioactivity. As the cat excretes the radioactive iodine in its urine and faeces, within a few days it will become less radioactive, and may well be moved to a larger pen. Different centres vary, but the cat will be able to go home after anything from five days to two weeks. However, it will continue to be radioactive to some extent for about six weeks after the injection date, so will need to be confined in a safe place in the home, cannot be cuddled or sleep with its owner, and its urine and faeces will need to be disposed of very carefully. But at the end of six weeks, the cat can live normally again, and will be completely cured.

Advantages of Radioactive Iodine Treatment

Radioactive iodine treatment is the most successful treatment for hyperthyroidism, working in nearly all cases. It has no side effects, and is a complete cure, rather than simply controlling the disease as medication or special diets will do. It is gentle and non-invasive for the cat, as it does not require an anaesthetic as surgery would do – though sedation may be used before giving the cat its injection. The hyperthyroidism never returns, although occasionally cats can get another thyroid tumour some years later – but this is unrelated to the first one. For these reasons many people consider it is the best alternative for a hyperthyroid cat.

Disadvantages of Radioactive Iodine Treatments

For many people, the main disadvantage is the cost. Radioactive Iodine Treatment is quite expensive, although costs at different centres do vary slightly. However, only one payment is required, and when compared with the costs of medication over a number of years and regular check-ups, there is not much difference- and radioactive iodine may even be the cheaper alternative. If you are insured, insurance will usually cover this treatment. And while it costs more than surgery, surgery is not guaranteed to work in all cases.

Occasionally cats will become hypothyroid, ie have thyroid hormone levels below the normal range. This is usually temporary. Even in the rare cases where it is permanent, thyroid supplementation has none of the side effects of hyperthyroidism drugs.

Another disadvantage for some people is that the cat has to be away from home for a period of time. Some owners worry that their cat will not cope well with this, particularly if it has never been separated from its owner before. They are also concerned about the rules when bringing their radioactive cat home – keeping the cat alone, not cuddling it, and so on. But cats are surprisingly resilient, and most of them cope very well with the situation.


Most owners whose cats have this treatment are delighted with the outcome. Indeed, my cat has just undergone this treatment, been pronounced cured, and I am really pleased that I decided to have it done. Indeed, for most cats who are in good health apart from being hyperthyroid, this is definitely the treatment of choice.

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