By Courtney Prue | May 17, 2025

Hyperthyroidism In Cats: Causes, Symptoms & Treatment

What is hyperthyroidism?

Hyperthyroidism is a common endocrine disorder affecting cats, that results from the overproduction of thyroid hormones by the thyroid gland. The thyroid gland is a butterfly-shaped endocrine gland located in the neck. The thyroid gland produces hormones that regulate the metabolic rate of the body, including heart rate, breathing, body weight, body temperature, and energy levels.

When a cat has hyperthyroidism, their metabolic rate is increased, leading to various physical and behavioural symptoms. Although cat hyperthyroidism can be effectively managed with the right diagnosis, treatment, and care, it can be distressing and life-threatening when left untreated or inadequately managed. As a cat owner, understanding the cause, symptoms, diagnosis, treatment options, and end-of-life care tips for hyperthyroidism can help you make informed decisions about your cat’s health and well-being.

How do I know if my cat has a thyroid disease?

Hyperthyroidism in cats can present with various symptoms, and the severity of the symptoms depends on the duration and progression of the condition. Signs of hyperthyroidism might include:

• Weight loss
• Increased appetite
• Increased vocalisation and/or restlessness
• Lethargy
• Increased heart rate
• Increased thirst and urination
• Vomiting & diarrhoea
• Changes in coat appearance

What happens if hyperthyroidism is left untreated?

Hyperthyroidism can have several consequences on a cat’s body due to the overproduction of thyroid hormones. Some of the common effects of hyperthyroidism on cats include:

• Weight loss: Hyperthyroidism can cause an increase in the metabolic rate, leading to the rapid burning of calories and subsequent weight loss.
• Changes in demeanor: Hyperthyroidism can cause cats to become restless or hyperactive and sometimes more irritable or aggressive
• Changes in coat condition: Hyperthyroidism can cause a deterioration in the coat appearance sometimes looking matted or unkempt.
• Heart problems: The increased metabolic rate caused by hyperthyroidism can put a strain on the heart, leading to high blood pressure, heart murmurs, and even heart failure.
• Gastrointestinal issues: Hyperthyroidism can lead to increased appetite, vomiting, and diarrhea, which can lead to dehydration and malnutrition.
• Kidney damage: The increased blood flow caused by hyperthyroidism can put a strain on the kidneys, leading to kidney damage or failure.

How is a thyroid disease diagnosed in cats?

A veterinarian will use various diagnostic tools to confirm a diagnosis of hyperthyroidism in cats. The diagnostic process may include:

• Physical examination: The vet will conduct a physical exam to check for any enlarged thyroid glands and other signs of hyperthyroidism, including high heart rate, ungroomed appearance, lean body condition, dehydration and more.
• Blood tests: A blood test will be carried out to measure the levels of thyroid hormones in the cat’s blood. An elevated level of thyroid hormones is an indicator of hyperthyroidism.

Follow-up or additional testing may include:

• Urinalysis: A urinalysis may be performed at the time or following initiation of treatment to evaluate kidney function and check for any signs of underlying urinary tract problems.
• Blood pressure: A blood pressure test will assess for any hypertension that may require treatment.
• Ongoing blood tests: Sequential blood tests will be performed regularly once treatment has begun to ensure the dosing is correct and the disease is under control.
• Weight checks: Weigh-ins should be completed regularly to ensure your pet’s weight is increasing or stable once a healthy body condition is reached. Weight is an indicator of how well the disease is being controlled with medication.

What medicine can I give my cat with hyperthyroidism?

Hyperthyroidism in cats can be effectively managed with the right treatment approach. The treatment options available for hyperthyroidism in cats include:

• Radioactive iodine therapy: This is a non-invasive treatment that involves the injection of a radioactive isotope into the cat’s body. The isotope targets the thyroid gland and destroys the overactive cells, leaving the healthy cells unaffected. Radioactive iodine therapy is considered the most effective and permanent treatment for hyperthyroidism in cats, with a cure rate of up to 95%. However, it may not be suitable for all cats, and a consultation with a veterinarian is necessary to determine the best course of action.
• Medications: Antithyroid medications, such as methimazole and carbimazole, can be prescribed to inhibit the production of thyroid hormones. This treatment is lifelong and requires daily administration of medication. The dose may need to be adjusted periodically, and regular blood tests will be required to monitor the cat’s thyroid hormone levels and ensure the medication is effective.
• Surgery: Surgical removal of the thyroid gland is another treatment option for hyperthyroidism in cats. This procedure is usually reserved for cats that are not candidates for radioactive iodine therapy or medication. This surgery does come with its own risks and complications.
• Diet: Some cats with hyperthyroidism may benefit from a special diet that is low in iodine, as iodine is an essential component of thyroid hormones. A low-iodine diet can help reduce the production of thyroid hormones and improve the cat’s symptoms.

The medical management and monitoring of hyperthyroidism can be confusing and overwhelming. Get in touch with our team today for a personalised discussion.

How long can my cat live with hyperthyroidism?

The prognosis for hyperthyroidism in cats can vary depending on the individual cat’s response to treatment and the severity of the condition. With appropriate management and treatment, many hyperthyroid cats can have a good quality of life and potentially a normal lifespan. However, it’s essential to work closely with your veterinarian to monitor your cat’s progress and adjust the treatment plan as needed.

Overall, early detection, proper treatment, and regular veterinary check-ups are crucial for managing hyperthyroidism effectively and ensuring the best possible outcome for your beloved feline friend.

How can I help my hyperthyroid cat at home?

Here are some tips to help you optimise your cat’s care at home:

• Assisted feeding: Cats with hyperthyroidism may have an increased appetite, and it’s essential to provide them with a well-balanced diet. Consider feeding your cat smaller, more frequent meals to help regulate their food intake.
• Hydration: Ensure fresh water is available at all times.
• Medical treatment: In addition to possible antithyroid hormone medications, other treatments your veterinarian might recommend include blood pressure medication, heart medication and more.
• Litter box maintenance: Make sure your cat’s litter box is easily accessible and clean.
• Environmental management: Keep your cat’s environment calm and stress-free.
• Create a comfortable living space: Ensure your cat’s living space is warm, quiet, and comfortable. Provide soft bedding, and ensure the area is clean and free of drafts.
• Manage stress: Try to minimise stress by keeping their routine consistent, minimising loud noises, and providing a calm environment.
• Regular check-ups: Your vet will monitor your cat’s condition and make changes to their treatment plan as necessary.

An in-home veterinary assessment can also be helpful to identify any other areas of improvement that can help your beloved cat stay comfortable for as long as possible.

End-of-life care tips

If your beloved cat’s hyperthyroidism has progressed to a point where treatment is no longer effective, it’s important to consider end-of-life care options, including possibly putting your cat to sleep (euthanasia). This can be an overwhelming and distressing thing to even think about. Rest Your Paws is here to support you and provide compassionate care for your beloved pet throughout their journey.
Here are some end-of-life care tips for your cat:

• Keep them hydrated and well-nourished with some delicious food
• Spend quality time with them, making the most of every moment, such as with a bucket list.
• Offer a calm and peaceful environment, free from stressors that can exacerbate symptoms
• Administer medications as prescribed, including for pain management and symptom relief
• Provide a warm and comfortable space for your cat to rest and sleep, with easy access to food, water, and a litter box
• Monitor your cat’s breathing, heart rate, and overall condition, and seek veterinary attention if necessary
• Evaluate their quality of life regularly, or reach out to a palliative care vet to help you with this.
• Consult our End of Life Care Pack to get prepared to put your cat to sleep.
• Track good days and bad days on our Quality of Life Assessment Calendar
• Rest Your Paws also offers full at-home Quality of Life Assessments to make sure your beloved pet is comfortable.

Hyperthyroidism in cats can be a challenging experience for both cats and their owners. However, with proper management, it is possible for cats to maintain a good quality of life. With the right care, support, and love, you can help your cat live a happy, healthy, and fulfilling life. Please do not hesitate to reach out to us if you have any questions or concerns – we are here to help.

Rest Your Paws

We offer in-home pet euthanasia for dogs, cats and other pets. Say goodbye with peace and dignity to your beloved pet. Professional and experienced end-of-life support.