Hyperthyroidism in Cats

What is Hyperthyroidism?

Hyperthyroidism is a common condition in older cats, where one or both thyroid glands (in the neck) become overactive and produce too much thyroid hormone. This hormone controls your cat’s metabolism, so an excess can cause the body to function too quickly.

Causes:

Most common: Benign tumour (adenoma) on the thyroid gland(s)

Rare: Malignant thyroid cancer

Occasionally unknown, but adenomas are by far the most frequent cause

What Are the Symptoms?

Cats with hyperthyroidism may show some or all of the following signs:

Weight loss despite good or increased appetite

Increased thirst and urination

Vomiting or diarrhoea

Restlessness or hyperactivity

Panting or difficulty breathing

Poor coat condition (matted, greasy, or unkempt fur)

Enlarged thyroid gland(s) in the neck (may be felt on examination)

How is Hyperthyroidism Monitored?

Monitoring helps ensure treatment is working and adjust care as needed.

Initial recheck: About 1 month after diagnosis, to assess treatment response

Ongoing checks: Every 3–6 months, depending on stability

Tests include: Blood work and physical examination

Treatment Options

1. Daily Medication

Often the first treatment option. Needs to be given consistently.

Available as:

Tablets

Oral liquid

Transdermal gel (applied to the ear)

2. Thyroidectomy (Surgical Removal)

Permanent solution in many cases

Requires anaesthesia and is available at many first-opinion and referral clinics

3. Radioactive Iodine Therapy

Highly effective, non-surgical treatment

Destroys overactive thyroid tissue

Only available at specialist centres

Requires a short hospital stay

Referral Process for Surgery or Radioactive Iodine

If you choose to pursue surgery or radioactive iodine treatment:

We cannot recommend specific clinics but encourage independent research

A referral form from us may be required

£25 admin fee applies (not typically covered by insurance)

Prognosis

Prognosis depends on the treatment and your cat’s response:

Medication: Many cats live several years with proper management

Surgery or Radioiodine: Excellent long-term outcomes in most cases

With appropriate treatment, many cats live 5+ years post-diagnosis

Possible Side Effects & Complications

Medication:

Vomiting

Lethargy

Loss of appetite

Behaviour changes

Surgery:

Rare risks to nearby tissues (e.g., parathyroid glands)

Radioactive Iodine:

Temporary isolation post-treatment

Rare risk of recurrence or other hormonal imbalances

Please contact us if you notice any new or worsening symptoms.

More Information

For trusted advice, visit:
🔗 International Cat Care – Hyperthyroidism in Cats