Hyperthyroidism in Cats

A ginger cat with hyperthyroidism rests, gazing thoughtfully, as it copes with its illness.

Understanding a Common Hormonal Disease in Older Cats

Hyperthyroidism is one of the most common hormonal diseases seen in older cats. It happens when the thyroid gland produces too much thyroid hormone, which speeds up the body’s metabolism.

In most cats, it is caused by a benign thyroid tumour or enlargement of the thyroid gland, not cancer. It is most often seen in middle-aged to older cats, especially those over 7 years of age.

Because thyroid hormone affects many parts of the body, hyperthyroidism can cause a wide range of symptoms. The good news is that once diagnosed, it can often be managed very successfully.

What Is Hyperthyroidism?

Too Much Thyroid Hormone

The thyroid gland produces hormones called T3 and T4. These hormones help regulate metabolism, heart function, body temperature, and energy use. In hyperthyroidism, the thyroid produces too much hormone, causing the body to work too hard.

This explains why many affected cats lose weight, seem restless, or eat more than usual.

Signs of Hyperthyroidism in Cats

Common Symptoms Owners Notice

Cats with hyperthyroidism may show signs such as:

• weight loss despite a good appetite

• increased appetite

• vomiting

• increased thirst

• increased urination

• hyperactivity or restlessness

• excessive vocalisation

• larger or more frequent stools

These are some of the most common clinical signs reported in specialist feline and endocrine references.

Some cats may also have a poor coat, muscle loss, or changes in behaviour. In some cases, the thyroid gland may be enlarged enough for your veterinarian to feel it in the neck during an examination.

Why Hyperthyroidism Matters

It Affects More Than Just Weight

Hyperthyroidism does not just cause weight loss. It can also place extra strain on the heart, kidneys, and blood pressure. This is why proper diagnosis and monitoring are so important.

In some cats, underlying kidney disease becomes more obvious after the thyroid disease is treated, so veterinarians often assess both conditions together.

How Veterinarians Diagnose Hyperthyroidism

Blood Tests Are the Key

Hyperthyroidism is usually diagnosed with a blood test measuring thyroid hormone, especially total T4. A high total T4 level in a cat with compatible signs usually confirms the diagnosis.

However, some affected cats can have a normal or borderline total T4, especially if they have another illness at the same time. In those cases, additional testing may be recommended.

Your veterinarian may also recommend:

• blood pressure measurement

• kidney blood tests

• urine testing

• heart assessment if needed

These tests help assess the overall health of the cat and identify any related problems.

Treatment Options for Hyperthyroidism

Several Effective Treatments Are Available

Cats with hyperthyroidism can be treated in several ways. Main treatment options include:

• radioiodine therapy

• antithyroid medication

• thyroid surgery

• iodine-restricted prescription diet

These are the standard treatment options described in specialist veterinary guidance.

Antithyroid Medication

Medication is commonly used to reduce thyroid hormone production. This can be a good option for many cats, especially when owners want a non-surgical treatment or when further monitoring is needed before deciding on a permanent option.

Radioiodine Therapy

Radioiodine treatment is often considered an excellent option because it targets abnormal thyroid tissue and can be curative in many cases.

Dietary Management

Some cats may be managed with a carefully controlled iodine-restricted diet, but this must be fed strictly and only under veterinary guidance.

Ongoing Monitoring Is Important

Rechecks Help Keep Cats Stable

Cats being treated for hyperthyroidism need regular veterinary monitoring.

Rechecks often include:

• weight checks

• blood tests

• kidney monitoring

• blood pressure assessment

This helps your veterinarian confirm that treatment is working and that your cat is tolerating therapy well.

Can Cats Live Well With Hyperthyroidism?

Yes, Many Cats Do Very Well

Yes. Many cats with hyperthyroidism do very well after diagnosis and treatment. Once thyroid levels are controlled, owners often notice improvement in appetite stability, weight, behaviour, and overall quality of life.

The earlier the condition is recognised, the sooner supportive care and treatment can begin.

Hyperthyroidism Care in Kalamunda

If your cat is losing weight, eating more than usual, becoming restless, or drinking more water, the team at Hilltop Veterinary Hospital in Kalamunda can assess your cat and check for hyperthyroidism or other common senior-cat conditions.

Early diagnosis can make a significant difference to your cat’s comfort and long-term health.

Concerned About Your Cat’s Health?

If your cat is showing signs such as weight loss, increased appetite, or behaviour changes, book a consultation with Hilltop Veterinary Hospital so our veterinary team can evaluate your cat and recommend the most appropriate treatment plan.

Explore More Pet Health Advice

For more veterinary advice on common cat health problems, explore our Pet Health Advice library.

You can also browse our Cat Health Care articles to learn more about kidney disease, appetite loss, vomiting, and other common feline medical conditions.

The information provided in this article is intended for educational purposes only and should not replace professional veterinary advice. Every cat’s medical situation is unique. If your cat is showing signs of illness, consult your veterinarian for proper diagnosis and treatment.