Wadestown Veterinary Clinic & Cattery
1 Grosvenor Tce, Wadestown, Wellington | PH 04 472 2012

Radioactive Iodine Treatment for Feline Hyperthyroidism/Thyrotoxicosis

Please click here to download a referral form for treatment of feline hyperthyroidism/thyrotoxicosis with radioactive iodine (I131).

Upcoming Radioactive Iodine (I131) Treatment Dates for 2024

Wednesday 13 March 2024
Tuesday 9 April 2024
Tuesday 7 May 2024
Wednesday 5 June 2024
Tuesday 2 July 2024 - 7 days only
Tuesday 20 August - 7 days only
Tuesday 3 September 2024
Tuesday 1 October 2024
Wednesday 30 October 2024
Tuesday 26 November 2024
Tuesday 14 January 2025

These dates are subject to change, however we will notify all patients booked in advance.

We will contact you requesting a non-refundable $250 deposit once your referring veterinarian has provided all the information required. Once you have paid the deposit we will contact you to confirm a date and time.

Veterinarians: please email the booking form (including client signature) and we will then contact your client. Please discuss all potential risks and ensure vaccinations are up to date before referral. 

Treatment of Hyperthyroidism

Is regarded as the "Gold Standard" treatment (the best).

**New prices effective 1st February 2024:

  • $1170.00 for treatment and 7 days boarding 
  • $1670.00 for treatment and 21 days boarding 
  • Repeat treatments FREE (including 7 day stay) if booked within 12 months of first treatment date.  Thereafter normal fees apply.  
  • Repeat treatments for bookings between March 2020 and August 2022 remain at $470.
  • Extra days are $35 per day. 
  • Cattery stays before and after treatment costs $25 per day.


  • Cost for 4 years treatment approx $1300 -$3500 (not including 6 monthly/12 monthly blood testing and consultations)
  • TWICE daily medicating with large tablets or ONCE daily with smaller more expensive tablets
  • Cats live on average 2 years with treatment (some cats are not suitable for radioactive iodine treatment)


  • Cost for 4 years treatment approx $6000-$6500 (not including 6 monthly/12 monthly blood testing and consultations)
  • ONCE DAILY medication required.
  • Cats live on average 2 years with treatment (some cats are not suitable for radioactive iodine treatment)


  • Hills y/d - this is a special type of dry food with very little iodine in it. This is only useful for indoor cats (that have no access to plants/soil) that live with no other pets. We have found this does not always result in controlled levels of thyroid hormone.

So your cat has been diagnosed with Hyperthyroidism ... here's what you should know.

Hyperthyroidism means overactive thyroid glands. The thyroid glands are situated in the cat's neck and play a vital role in the control of the body's metabolic rate. An increased production of thyroid hormones leads to an increased metabolic rate which is reflected in the classic symptoms:

  • Weight loss
  • Increased or very good appetite
  • Increased water intake
  • Increased irritability
  • Restlessness
  • Fast heart rate
  • Sometimes howling at night
  • Sometimes vomiting and diarrhoea
  • Unkempt coat

The clinical signs caused by hyperthyroidism can be quite dramatic and cats can become seriously ill. These cats often look older as the disease is wearing their bodies out fast!


Hyperthyroidism can lead to changes in the heart, as it elevates the heart rate and makes the heart work harder. Over time the heart muscle gets enlarged and thickened and if untreated this can lead to breathing difficulties and heart failure.


Hyperthyroidism can also lead to high blood pressure in some cats and this can cause additional damage to other organs like the heart, brain, eyes and kidneys. In many cases hypertension will resolve with the treatment of the hyperthyroidism but some cats need additional medication.

Kidney disease

Due to the often advanced age of hyperthyroid cats, chronic renal failure can be another complicating factor, as this is also a common disease in older cats. Hyperthyroidism often improves blood pressure in the kidneys and this improves their function. When the hyperthyroidism is treated this can often unmask poor kidney function so a fine balance needs to be found between treating the overactive thyroid and supporting the kidneys.

Blood clots

Due to the combination of heart changes and blood pressure changes cats can end up with blood clots. These cause symptoms associated with where they lodge in the body - eg in the brain it cause seizures or changed behaviour, in the spine it can cause paralysis (often permanent), in the lungs it can cause difficulty breathing. 


Medical treatment

This is not a curative treatment but can be used long-term. To control the thyroid function, anti-thyroid drugs are given in the form of tablets. The tablets are usually given once or twice a day for the rest of your cat's life. Initially your cat will need one or two follow up blood tests to establish the correct dose and then regular bloods tests are required every 6-12 months long-term. Delaying curative treatment (radioactive iodine) by waiting more than 1 year after diagnosis unfortunately increases the risk of your cat's condition becoming cancerous and non-responsive to medical treatment and radioactive iodine treatment.

Radioactive iodine treatment

This might sound a bit scary but it is the current treatment of choice for most hyperthyroid cats as it is a safe and effective cure.

Radioactive iodine is administered as an injection under the skin which then selectively destroys the abnormal thyroid cells. This is curative in 95% of all hyperthyroid cases. There is usually a mild sedative given beforehand and there are no direct side effects or radiation sickness.

Because this treatment involves the handling of radioactive substances it can only be performed in special licensed facilities. We act as a referral clinic for this treatment, so if your cat has been diagnosed with hyperthyroidism by your vet, they can contact us to discuss treatment options.

The patients are hospitalised for one week in a special facility until the radiation level has fallen to acceptable limits. They can then be discharged and taken home with special instructions in regards to their care and handling over the next two weeks or there is the option to board cats for the entire three weeks. Medication is not required after radioactive iodine treatment. The cats will require a follow up blood test 3 months after the treatment to show the effectiveness of the treatment and to monitor kidney function. 

Common Questions

  • How is the treatment given? A mild relaxant/sedation is given orally before treatment and when they are feeling happy, the iodine is injected under their skin (similar to a vaccination). They then stay in our designated boarding facilities for 7 or 21 days.
  • Will my cat suffer side effects such as vomiting or hair loss? No
  • What do I feed after treatment? Your cats preferred diet.
  • Are there any risks with treatment? The treatment itself is very safe. However there are many risks associated with having high levels of thyroid hormone before, during and after treatment (see above list). So please ensure you have discussed all risks for your cat and yourself with your current veterinarian.
  • What if my cat becomes stressed during their stay? We would usually recommend a 7 day stay if your cat gets particularly stressed which results in medical conditions (eg peeing blood). We occasionally give appetite stimulants to encourage appetite and this often reduces stress as well. 
  • Does treatment always work? Radioactive iodine treatment is curative for 95% of cats. In the remaining 5% a second dose is usually curative - we provide this second treatment for free if booked in within one year of the first treatment.
  • When is it best to treat my cat? Your vet will usually do a 'treatment trial' with medication if appropriate, for approximately a month. If your cat is a good candidate, we recommend booking in as soon as possible after diagnosis. Delayed treatment (waiting more than 1 year after diagnosis) increases the risk of your cat's condition becoming cancerous and non-responsive to medical treatment and radioactive iodine treatment. 
  • How do I decide if a 7 day stay or 21 day stay is better? Please look at Page 2 of the referral form - this shows what care is required at home between days 7-21. If your cat gets stress related medical conditions we recommend a 7 day stay.

Vaccinations Before Radioactive Iodine Treatment

These need to be up to date (within the last year). If a vaccine has not been given within the last three years, we recommend a course of two vaccinations be given 2-4 weeks apart. Ideally their final booster is at least 2 weeks prior in case they become unwell after vaccination/have a reaction. We appreciate there are variations in what veterinarians recommend however we base our requirement on the risk to your cat, our staff and current research. 


If your cat is referred for radioactive iodine treatment, it is important that they are fed only a premium diet for at least 2 weeks prior to treatment, as failure to do so can prevent the treatment from being successful. In this case, ensure the premium diet consists of absolutely no fish or fish-based foods, commercial jellymeats or foods high in iodine. To be safe, we recommend Royal Canine, Hills Science Diet or Iams chicken-based foods. If you have any queries about this or if your cat already has specific dietary requirements please ensure you or your vet checks with us that the food is suitable to give your cat prior to treatment.

We also strongly suggest that you check that your cat is not getting food from anywhere else, e.g. that your neighbours are not feeding them. If your cat is hyperthyroid then they are likely to be seeking out food wherever they can, and may be well known around the neighbourhood. If your cat has access to non-premium foods elsewhere, treatment success is still jeopardised despite having a premium diet at home.

  • We do not recommend feeding just meat or raw meat due to the unknown levels of iodine and risks of infection.
  • Your cat will need to be fed more meals (eg three or four meals per day) in the two weeks leading up to treatment and for a few months after treatment as their thyroid hormone levels will be above normal and they can lose significant weight in this time. 

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