Hyperthyroidism
What is it?
Hyperthyroidism is an overactive thyroid gland, usually from a benign growth. Excess hormone speeds up the metabolism. It is one of the most common hormone disorders in cats over ten.
What signs should I watch for?
Signs to watch for include weight loss despite a big appetite; increased thirst and urination; restlessness, vocalizing at night; vomiting or diarrhea; and unkempt coat, fast heart rate.
How is it diagnosed and treated?
A blood test measuring thyroid hormone usually confirms it. Options include daily medication, an iodine-restricted diet, radioactive iodine therapy (often curative), or surgery.
Can it be prevented, and what's the outlook?
- With treatment, the outlook is generally good.
- Untreated, it can damage the heart and raise blood pressure.
- Kidney function should be monitored during treatment.
Reviewed by the Adler Veterinary Hospital veterinary team, October 2026.
Cats over ten years old
Who's at risk:
Weight loss despite big appetite, thirst, restlessness, vomiting
Main signs:
Ongoing management with your vet
Urgency:
When to call a vet right away
- Sudden blindness
- Not eating
- Vomiting, lethargy, fever or not eating after starting thyroid medication
- Unusual bleeding while on thyroid medication
- Frequent vomiting or diarrhea
Not sure whether it can wait? Call us anyway. Our team can help you decide.
Source:
Related conditions
Diabetes
IBD & GI Lymphoma
Obesity