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Hyperthyroidism in Cats
Overview
Hyperthyroidism in cats is a common endocrine (hormone) disorder in which the thyroid gland produces excess thyroid hormones. The condition affects about 10% of cats over the age of 10. If left untreated, hyperthyroidism can contribute to significant health issues, such as heart disease, high blood pressure and kidney problems. However, the right approach can manage or even cure the condition, enhancing your cat’s quality of life and overall well-being.
What are the symptoms of hyperthyroidism?
The most common symptoms of hyperthyroidism in cats are:
- Weight loss despite an increased appetite
- Vomiting
- Increased thirst and urination
- Behaviour changes like restlessness, crying, or agitation
- An unkempt coat or poor grooming habit
In more severe cases, hyperthyroidism can lead to heart disease, which may cause your cat to breathe rapidly or struggle with physical activity.
Early detection and treatment are the key to preventing serious complications and allowing your cat to return to their wonderful best.
Radioactive iodine treatment
Radioactive iodine is the only curative treatment for hyperthyroidism in cats. The treatment targets overactive thyroid tissue with a small dose of iodine, sparing healthy areas. It requires a brief isolation period afterwards.
PROS
- A curative treatment that is considered the gold standard
- One treatment usually resolves the issue, avoiding ongoing medication
- Minimally invasive, targeting only the thyroid and reducing side effects
- Typically, more cost-effective in the long run compared to other treatments
CONS
- Requires a week of isolation in a specialist facility due to radioactivity level
- Unsuitable for some cats with underlying medical conditions
- Dosage determination requires an experienced specialist team for the best outcomes
Cat Specialists Services offers a world-class radioactive iodine treatment facility specifically designed to create a stress-free environment that supports the well-being of cats during their stay.
Dietary modification
PROS
- Non-invasive treatment requiring only dietary changes
- Useful for owners who prefer to avoid daily medications
CONS
- Not a curative treatment; symptomatic relief only
- Requires strict adherence, which is difficult for multi-pet
households - Unsuitable for cats needing different food for other
conditions
In the dietary management of hyperthyroidism in cats, iodine intake is restricted through targeted dietary management, effectively reducing thyroid hormone production. This helps to control some hyperthyroid symptoms.
Oral medication
PROS
- Widely available in tablets or liquid form
- Non-invasive and effective if used consistently
CONS
- Not a curative treatment; some symptomatic relief only
- Ongoing medication and monitoring make this the most expensive option after 1-2 years of treatment
- Prolonged use increases the risk of disease progression to the more serious thyroid carcinoma
- Some cats are hard to medicate, causing stress for you and your cat
Oral medications control hyperthyroidism symptoms but don’t cure the condition, and long-term use may escalate costs and increase disease risk.
Surgery
A surgical procedure can remove the affected thyroid gland in cats with hyperthyroidism. This is rarely chosen due to the availability of less risky, more effective and less expensive treatments.
PROS
- Offers a quick solution for patients needing immediate results
- Potentially curative when other treatments are not viable
CONS
- Not as reliable in curing the condition as radioactive iodine treatment
- There are significant associated risks, including anaesthesia, surgical and post-surgical complications
- Used mainly for cases where radioactive iodine is unsuitable, like severe heart disease
A few facts about hyperthyroidism and cats
All mammals, including cats, have two thyroid glands in the neck, one on each side of the windpipe (trachea). These glands usually are about 4-8 mm wide and 10-20 mm long. Their primary function is to produce thyroid hormones like T4 (thyroxine) and T3 (triiodothyronine), which regulate metabolism—the process of turning food into energy.
In cats with hyperthyroidism, these thyroid glands enlarge, which can often be felt by gently touching the cat’s neck.
Hyperthyroidism causes the glands to produce too much thyroid hormone, which affects almost every part of the cat’s body.
Thyroid hormones are crucial in regulating the body’s metabolic rate or how quickly the body uses energy from food. These hormones influence the function of every cell and organ, including the heart, digestive system, and muscles. In hyperthyroid cats, the metabolic rate increases, which explains why affected cats often lose weight despite eating more than usual.
In addition to weight loss, excessive thyroid hormone levels can also:
- Speed up or slow down the heart rate
- Raise or lower body temperature
- Increase the speed at which food passes through the digestive tract
Hyperthyroidism in cats was first reported only about 40 years ago, it is now recognised as the most common hormonal disorder in cats worldwide. Interestingly, this condition is more prevalent in cats than other domestic animals, but the reasons for this are not entirely understood.
Despite extensive research, the underlying cause of hyperthyroidism in cats remains unclear. However, several factors may contribute to the development of the disease, including:
- Iodine deficiency or inconsistent iodine levels in the diet
- Long-term exposure to thyroid-disrupting chemicals, such as BPA (found in some plastics) and
- PBDEs (used in flame retardants)
- Cats may be more vulnerable to these chemicals due to their grooming habits, increasing their exposure to contaminants.
Although we don’t fully understand why hyperthyroidism occurs more frequently in cats, it’s clear that this condition can have serious health effects. Understanding how the thyroid glands work and the impact of thyroid hormones on a cat’s body can help cat owners recognise early symptoms and seek treatment quickly.
“Hyperthyroidism is one of the most common endocrine disorders in older cats.”
Are you worried about your cat’s health?
If you are concerned about your cat, please reach out to our friendly team. Call us on 1300 228 377 or fill out the contact form below. In an emergency, please contact your local vet.
For vets – to refer a patient or book a telehealth consultation, please call us on 1300 228 377, book through the portal or fill in the form.
Meet The Author
Dr Rachel Korman
Specialist in Feline Internal Medicine
BVSc MANZCVS (Internal Medicine) FANZCVS (Feline Medicine)
Dr. Korman’s childhood love for cats led her to veterinary medicine, and early on, it was clear that feline care was her calling. After graduating from the University of Queensland in 2000, she worked in small animal and feline-only practices across Australia and the UK.
She received a Senior Clinical Training Scholarship from the Feline Advisory Bureau (now International Cat Care) at the University of Bristol, where she researched feline infectious and haematological diseases, and in 2018, became a Fellow of the Feline Medicine Chapter of the Australian New Zealand College of Veterinary Scientists and a registered Feline Medicine specialist.
Frequently Asked Questions
What is hyperthyroidism in cats?
Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone. This hormonal imbalance affects metabolism and can lead to multiple health issues.
What symptoms might a hyperthyroid cat show?
Common signs include weight loss despite a strong appetite, vomiting and increased thirst or urination. Behaviour changes such as restlessness may also occur.
Which cats are most affected by hyperthyroidism?
The condition is most often seen in older cats. Studies suggest it affects around 10% of cats over 10 years of age.
What treatments are available for hyperthyroidism?
Treatment options may include medication, dietary management or radioactive iodine therapy. Radioactive iodine specifically targets abnormal thyroid tissue.
Why is early diagnosis important for hyperthyroidism?
Early detection allows treatment before complications develop. Untreated hyperthyroidism can lead to heart disease, high blood pressure or kidney problems.
Patient Stories
Our commitment to feline health is best seen in the stories of the cats we’ve had the privilege of treating. These journeys highlight the dedication, expertise and compassion that drive us.
Each patient faced unique challenges, and it was our honour to offer high-quality care and help them regain strength and happiness. We value the deep bonds with cats and their owners, knowing the difference we make in their lives.
Kitty, a lymphoma survivor
We first met Kitty after she was referred to CSS for the evaluation of a large intestinal mass
Poppi finds her feet again
Following surgery to remove a hairball obstruction, Poppi was referred to us at CSS as she had not bounced back as expected
Rusty and his ongoing chronic rhinitis journey
Lifelong nasal issues, including persistent discharge and breathing noise, have been a bit of a thorn in Rusty’s side.
Lando’s long game with cryptococcus
Lando was referred to CSS because he had a swelling under his jaw that wouldn’t go away.
Popeye coughs up the culprit
Ares is a handsome young Maine Coon who was referred to CSS after presenting at AES with sudden lameness in his back leg.
Key Takeaways
Hyperthyroidism is a hormonal disorder where the thyroid gland produces excessive thyroid hormone.
Symptoms often include weight loss despite increased appetite and changes in behaviour.
Radioactive iodine therapy is considered a curative treatment for many cats.
Cat Specialist Services Reviews 
on 
Tanya Bell
6 months ago
We transported our cat here from another animal hospital, as his condition was too complex for them. Our pet was given the highest quality of care, multiple investigations/procedures being able to be done at the one place a godsend. We were kept up to date frequently throughout his stay. All questions & options explained thoroughly. Being able to have private visits certainly helped us and our cat too. I would highly recommend Cat Specialist Services at Underwood. Amazing staff from reception, vet nurses, vets & specialists. Oh, and yes he is recovering wonderfully at home.
Melinda Cox
A month ago
So very happy we were asked to come here for advice for our NORBIT. He has had 2 x UTI blockages within weeks of each other since turning 6. Surgery seemed to be his only option and he didn’t feel it was very fair on him if we didn’t at least exhaust all other avenues first.
Dr Allison was very thorough in her tests and has let us know she would like to treat the cause of the problem. Great news.
It may lead to removal of crystals in his bladder if his diet doesn’t let him pass them naturally.
At least this surgery won’t be as severe at taking his penis off him – so as his fur parents – we are very happy with this.
We await further tests to see what’s in store for him.
NORBIT will now be a patient of the clinic as we are so far very happy with his treatment thus far.
Lesley Rosekrans
A month ago
Hi has only been a week since losing my beautiful Peaches but can’t thank Dr Cindy, Maree and Jackie enough for the tender care they gave her and they after care they gave me. I sincerely thank them and can’t recommend the Clinic highly enough they are such caring people. Peaches I’m happier times.
Madison McEwan
A month ago
I cannot thank the entire CSS team enough and especially Dr Cindy for the care they provided for our boy with a urinary blockage, and we will be taking both our cats here from now on. The clinic is exceptionally clean and calming compared to all other clinics we’ve been too, and all staff from the reception to the nurses/vets were so supportive during a stressful time. I knew from the first minute that I got to see him after he was transferred that he was in the best place, and that the staff genuinely care about their well-being and positive long term outcomes. We were given regular updates and full transparency, so much information including QR video codes on how to administer medications, along with print outs and emails about how to best help avoid future issues or recurrence. Our boy got to smooch on everyone and was beyond well looked after. Thank you again, you all made an incredibly stressful situation actually manageable and calming.
Astrid El Gamal
6 months ago
Dr Wan-Ju has been treating my baby since her first seizure in November 2025 and she has been fantastic.
Everybody at the clinic is so friendly and caring and I know my baby is in good hands.
Thank you team!
Deeba M
3 months ago
Dr Alison Jukes from CSS Underwood is an AMAZING feline physician. She is kind, professional, thorough and our cat is blessed to have her on his side. She even was able to save us money and invasiveness by being skilled to the level of doing ultrasound on two separate occasions without our cat needing to go under full sedation. Our other cat was recently seen by Dr Jukes as well, and she made sure our cat’s heart was ok. I also want to thank the lovely Jacqueline and Mairead from customer care. They are very kind each time I see them and call up. Sending thanks from our family, including Smokey and Floozy!
Judith Dionysius
A month ago
My whole experience with CSS was positive – from the first email I received giving lots of information regarding the process of radioactive iodine treatment to the expected costs, to checking my cat in for the treatment, boarding for 2 weeks after the treatment and picking her up to come home. They didn’t push for any tests that were not necessary.
Janelle Wieden
5 months ago
We never knew this service existed but we are very grateful we were referred to them. Our vet Cindy was really great, she made us feel at ease during a very stressful time. We got the sense straight away the Leo was in good hands. This service made us feel better knowing that they specialise is cats only. Would highly recommend their services
Georgia Carter
5 months ago
My Lani finished her I-131 treatment today and I am beyond impressed with the way she was looked after. I am by definition a neurotic pet owner and sending my fur child away for a week was seriously daunting.
I was given daily updates about how kitty was eating, toileting and behaving. This really put my mind at ease. Vets and vet nurses were so accomodating and allowed Lani to have her favourite foods from home prepared her favourite way.
Her vet was so thorough when explaining her treatment and condition to me.
The ladies at reception were so friendly and understanding.
I honestly cannot recommend this clinic enough and I am so thankful for the positive experience Lani and I have had.
Lauren Woodward
A year ago
My sweet ginger boy Louis was hospitalised at CSS for a Urinary Obstruction. Dr Cindy and all the reception staff were amazing and empathetic. I would often ring up with questions post procedure and Dr Cindy would make time to talk and explain things to me
Service Locations
Cat Specialists accepts referrals for cats across Brisbane and surrounding regions, working closely with local veterinary clinics to provide specialist diagnosis, treatment, and ongoing management.
Contacting Us
Pet Owners
If you would like to talk about treatment for your cat, call us on 1300 228 377 or fill in the form.
In an emergency, please contact your local vet.
Vets and Nurses
To refer a patient or book a telehealth consultation please call us on 1300 228 377, book through the portal or fill in the form. For advice calls, please see the guidelines here.
Monday-Friday: 8 am-6 pmSaturday/Sunday - Closed