Hyperthyroidism in cats
Hyperthyroidism is an overactive thyroid gland, usually from a benign growth. It's the most common hormone disorder in older cats.
Last updated: October 2026 · 3 sources · see sources
Signs to watch for
- Weight loss with a big appetite
- Restlessness
- Vomiting
- Drinking more
- Unkempt coat
- Fast heart rate
Trouble breathing, collapse, repeated vomiting, not peeing, or a seizure that lasts more than a few minutes needs a vet right away. See when to see a vet.
How vets diagnose it
A blood test for thyroid hormone (T4) usually confirms it. Your vet also checks the kidneys and blood pressure. [2][3]
How it's treated
Options are daily methimazole, a prescription iodine-restricted diet, radioactive iodine (I-131) or surgery. [2][3]
Medicines your vet may mention: Methimazole. We don't list doses; your vet will decide what fits your pet.
What it costs to diagnose and manage
| Item | Typical US price | Src |
|---|---|---|
| Diagnosis (exam and tests) | $100–$300 | [1] |
| Ongoing treatment, per month | $20–$35 | [1] |
| Ongoing treatment over a year (monthly range × 12) | $240–$420 | [1] |
These are typical US ranges from the sources listed. Your pet's costs depend on how severe things are, the tests your vet recommends, your pet's size and where you live. Ask your vet for a written estimate.
Outlook
Most cats do very well with treatment. Radioactive iodine cures most cats. [2][3]
Common questions
What is hyperthyroidism in cats?
Hyperthyroidism is an overactive thyroid gland, usually from a benign growth. It's the most common hormone disorder in older cats.
What are the signs of hyperthyroidism?
Common signs include: weight loss with a big appetite, restlessness, vomiting, drinking more, unkempt coat, fast heart rate.
How do vets diagnose hyperthyroidism?
A blood test for thyroid hormone (T4) usually confirms it. Your vet also checks the kidneys and blood pressure.
How is hyperthyroidism treated?
Options are daily methimazole, a prescription iodine-restricted diet, radioactive iodine (I-131) or surgery.
How much does hyperthyroidism cost to treat?
Diagnosis (exam and tests): $100–$300; Ongoing treatment, per month: $20–$35; Ongoing treatment over a year (monthly range × 12): $240–$420. Costs vary with severity, tests, your pet's size and where you live.
Related
This page is general information for pet owners, not veterinary advice. Talk to your vet about your own pet.