Pocket VetHyperthyroidism in cats
Hyperthyroidism is a common hormone disorder in older cats, where an overactive thyroid speeds up metabolism. It's very treatable.
What it is
A usually-benign thyroid enlargement overproduces thyroid hormone, revving up metabolism. It typically affects cats over 10 and strains the heart and kidneys if untreated.
Symptoms
- ●Weight loss despite a strong (often increased) appetite
- ●Hyperactivity, restlessness, or irritability
- ●Increased thirst and urination
- ●Vomiting or diarrhea
- ●Unkempt coat, fast heart rate
🔴 When to act now
- ●Laboured breathing, collapse, or sudden weakness
- ●These can signal heart complications — see a vet urgently
Treatment & management
Diagnosed with a blood test, it's treated with daily medication, a special iodine-restricted diet, radioactive iodine therapy (often curative), or surgery. Treatment usually reverses the symptoms and protects the heart and kidneys.
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Check my cat nowFrequently asked
What is the first sign of hyperthyroidism in cats?
Weight loss despite eating well is the classic early sign, often with increased thirst, restlessness, or vomiting in an older cat. A blood test confirms it.
Is hyperthyroidism in cats curable?
Yes — radioactive iodine therapy cures most cases. Daily medication and prescription diets also control it well. Early treatment protects the heart and kidneys.
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Pocket Vet editorial team
Written and maintained by the Pocket Vet editorial team using authoritative veterinary sources. Reviewed June 9, 2026. This guide is informational only and not a substitute for professional veterinary care — see our editorial & safety policy. When in doubt, contact your vet; in a true emergency, go to an emergency clinic immediately.
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