Hyperthyroidism is the most common hormonal disorder in cats, typically affecting those over 10 years old. The thyroid gland produces excess hormone, accelerating the cat’s metabolism. Left untreated, it leads to heart failure, high blood pressure, kidney damage, and death. The good news: it is one of the most treatable conditions in feline medicine.
Symptoms
- Weight loss despite increased (often ravenous) appetite — the classic sign
- Hyperactivity, restlessness, irritability
- Increased thirst and urination
- Poor coat condition — matted, greasy, or unkempt
- Vomiting and diarrhoea
- Rapid heart rate (tachycardia)
- Palpable thyroid swelling (goitre) in some cats
Treatment Options
| Treatment | Curative? | UK Cost |
|---|---|---|
| Radioactive Iodine | Yes — 90–99% cure rate | £1,800–£3,400 |
| Surgery (Thyroidectomy) | Yes | ~£719 |
| Methimazole tablets | No — lifelong | £25–35/month |
| Transdermal gel (ear) | No — lifelong | £30–60/month |
| Low-iodine diet (Hill’s Y/D) | No — strict compliance | 80p–£1.20/day |
Important Warning: Kidney Disease
Hyperthyroidism increases blood flow to the kidneys, which can mask underlying chronic kidney disease (CKD). When thyroid levels are normalised (by any treatment), kidney values may rise. This is why vets often trial methimazole medication first — to check kidney function before committing to permanent treatment like radioiodine.
FAQs
Radioiodine or medication — which should I choose?
Radioiodine is the gold standard because it cures the condition in a single treatment with minimal side effects. However, it requires 5–14 days’ hospitalisation at a specialist centre, and the upfront cost (£1,800–£3,400) is significant. Lifelong medication avoids the upfront cost but accumulates: at £30/month, you’ll spend £1,800 over 5 years — plus regular blood test costs. If your cat is otherwise healthy and a good candidate, radioiodine is usually the most cost-effective long-term option.
Reviewed by Dr. Sarah Jenkins, MRCVS
Dr. Jenkins is a fully practicing veterinary surgeon in the UK with over 15 years of clinical experience in small animal medicine and canine behaviour. She reviews and verifies our health content to ensure medical accuracy.
