Hyperthyroidism in Cats: Symptoms, Treatment & Cost

By the Pawlee Team

Diagnosis cost

£150–£400

Treatment cost

£300–£3000

Ongoing cost

£30–£60 per month

Severity

Moderate

Treatable

Yes

Species

Cats

What is hyperthyroidism?

Hyperthyroidism is the most common hormonal disorder in cats, caused by an overactive thyroid gland producing too much thyroid hormone. In the vast majority of cases, it’s caused by a benign (non-cancerous) enlargement of the thyroid gland. The excess hormones speed up the cat’s metabolism, causing weight loss, restlessness, and increased appetite. It primarily affects cats over the age of 8. Left untreated, hyperthyroidism can cause serious damage to the heart and kidneys.

Symptoms to watch for

See a vet soon

Weight loss despite a good or increased appetite
Increased thirst and urination
Restlessness, hyperactivity, or vocalising more than usual
Vomiting or diarrhoea
Poor coat condition or excessive shedding
Rapid heart rate or heart murmur
Occasionally: lethargy and loss of appetite (apathetic hyperthyroidism)

How is hyperthyroidism diagnosed?

Test	Typical cost
Blood test (total T4 thyroid hormone level)	£80–£200
Full blood panel and kidney function tests	£100–£250
Blood pressure measurement and heart assessment	£40–£80

Treatment options and costs

Daily medication (methimazole / Felimazole)

£30–£60 per month ongoing

Oral tablets or transdermal ear gel given once or twice daily to control thyroid hormone levels. This is the most common treatment and is effective at managing symptoms, but must be continued for life. Regular blood tests every 3–6 months are needed to monitor levels and kidney function.

Radioactive iodine therapy (curative)

£1,500–£3,000 (one-off)

A single injection of radioactive iodine that destroys the overactive thyroid tissue. This is the gold-standard treatment and is curative in over 95% of cases with no ongoing medication needed. The cat must stay in a specialist facility for 1–4 weeks due to radiation safety requirements.

Prescription thyroid diet (Hills y/d)

£40–£70 per month ongoing

An iodine-restricted diet that limits the raw material the thyroid needs to produce hormones. Can be effective as a sole treatment if the cat eats nothing else, but this is difficult to achieve in multi-cat households or cats with outdoor access.

Ongoing costs

Estimated ongoing management cost

£30–£60 per month

monthly

Breeds most at risk

Breed	Risk level
Siamese	Moderate
Persian	Moderate
British Shorthair	Moderate
Ragdoll	Moderate
Maine Coon	Moderate

Does pet insurance cover hyperthyroidism?

Hyperthyroidism is covered by most lifetime pet insurance policies for diagnosis, medication, and monitoring. Radioactive iodine therapy is usually covered too, though it’s worth checking as some policies have limits on specialist treatment or require a referral. Because daily medication is needed for life, a lifetime policy is far better value than a time-limited one. Pre-existing hyperthyroidism will not be covered by a new policy.

Related conditions

Kidney Disease Cats Diabetes Cats Heart Murmur Dogs

Frequently asked questions

How much does it cost to treat hyperthyroidism in cats?

It depends on the treatment route. Daily medication costs £30–£60 per month indefinitely, plus £100–£200 for monitoring blood tests every 3–6 months. Over a cat’s remaining lifetime (often 3–5 years), this totals £2,000–£5,000. Radioactive iodine therapy costs £1,500–£3,000 as a one-off but is curative and often works out cheaper in the long run.

Is radioactive iodine treatment worth the cost?

For most cats, yes. It’s curative in over 95% of cases with a single treatment, has very few side effects, and eliminates the need for daily medication. Over 3–5 years, the cost of ongoing tablets plus regular blood tests often exceeds the one-off cost of radioactive iodine. The main drawback is that the cat must be hospitalised for 1–4 weeks in a specialist facility.

What happens if hyperthyroidism is left untreated?

Untreated hyperthyroidism progressively damages the heart, causing thickening of the heart muscle (hypertrophic cardiomyopathy) that can lead to heart failure. It can also mask underlying kidney disease that becomes apparent once treatment starts. Affected cats continue to lose weight, become increasingly restless, and their quality of life deteriorates significantly.

How common is hyperthyroidism in cats?

Very common. It’s the most frequently diagnosed hormonal condition in cats, affecting an estimated 1 in 10 cats over the age of 10. All breeds are susceptible, though Siamese cats may develop it slightly earlier. The prevalence has increased significantly over the past few decades, possibly linked to environmental factors or improved detection.