Hyperthyroidism in Cats: Signs, Diagnosis and Treatment

Hyperthyroidism is one of the most common conditions in older cats. It happens when the thyroid glands produce too much thyroid hormone, which speeds up the whole body. It is treatable, and many cats do very well once it is diagnosed.

Signs to look for

• Weight loss despite a good or increased appetite
• Drinking and urinating more
• Restlessness, hyperactivity or increased vocalising, especially at night
• Vomiting or loose stools
• A greasy or unkempt coat
• A fast heartbeat
• Sometimes the opposite: some cats become quiet and lose their appetite

It usually affects cats aged around 10 and over. Because the signs can look like normal ageing, it is easy to miss. Regular senior checkups help catch it early.

Why it matters

Untreated hyperthyroidism can strain the heart and raise blood pressure, and it can affect the kidneys and eyes. Early diagnosis protects your cat’s long term health.

How is it diagnosed?

Your vet will examine your cat, feel the neck for an enlarged thyroid and check blood pressure, then run a blood test to measure thyroid hormone. They may also check kidney function, because treating hyperthyroidism can reveal kidney problems that were masked.

Treatment options

• Daily medication (tablets or liquid) to control hormone levels. This is lifelong and needs regular blood tests.
• A prescription diet low in iodine, as the only food your cat eats.
• Radioactive iodine treatment, a single treatment at a specialist centre that often cures the condition.
• Surgery to remove the affected gland, which is less common.

The best option depends on your cat’s age, other conditions and your budget. Be honest with your vet about what you can manage, because there are choices.

Caring for your cat

• Give medication at the same time each day, and ask for tips if tablets are difficult.
• Keep up regular checkups and blood tests.
• Weigh your cat regularly and note any changes.
• Keep water available and your cat’s routine calm.

Last updated: October 2026. This article is general information and is not a substitute for advice from your vet. If you are worried about your cat, or cannot afford their care, please contact us and see our guide to what to do if you cannot afford vet bills.

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