Hyperthyroidism is one of the most common conditions we diagnose in older cats at Paws & Co Veterinary Centre. It’s caused by the overproduction of thyroid hormone, which drives up metabolism and affects almost every system in the body. The good news is that with early diagnosis and the right treatment, most cats do very well.
If your older cat seems to be eating more but losing weight, or has become restless and vocal, hyperthyroidism should be high on the list of possibilities. Here’s what you need to know.
What Is Hyperthyroidism?
The thyroid glands, located in the neck, produce hormones that regulate metabolism. In hyperthyroidism, a benign growth on the thyroid gland causes it to produce too much hormone. This sends the body’s systems into overdrive — the heart beats faster, the digestive system speeds up, muscle is broken down for energy, and weight is lost despite a ravenous appetite.
Most affected cats are over 10 years old, although it can occasionally occur in younger animals. It affects male and female cats equally and is not related to lifestyle.
Signs and Symptoms
⚖️ Weight Loss
Despite eating well — often eating more than usual — affected cats lose weight steadily. This is one of the most consistent and noticeable early signs.
💨 Increased Activity
Hyperactivity, restlessness, and increased vocalisation — particularly at night — are common. This is the thyroid hormone driving the nervous system.
💧 Increased Thirst
Drinking and urinating more than usual. This can also indicate concurrent kidney disease, which is common in older cats and important to assess before starting treatment.
Other signs include a poor, unkempt coat, vomiting, diarrhoea, a rapid or irregular heartbeat, and in advanced cases, heart disease. Some cats show the opposite of hyperactivity — becoming quiet, weak, and depressed. This is sometimes called “apathetic hyperthyroidism” and can be missed if only the classic presentation is expected.
Diagnosis
Diagnosis is straightforward — a simple blood test measuring thyroid hormone (T4) levels is usually all that’s needed, alongside a physical examination where we may be able to feel an enlarged thyroid gland in the neck. We’ll also check kidney function, as the two conditions often coexist and the interaction between them affects which treatment we recommend.
Treatment Options
- Medication — daily oral tablets (methimazole or carbimazole) reduce thyroid hormone production. Effective and reversible, allowing us to assess kidney function before committing to a permanent option
- Prescription diet — a strictly iodine-restricted diet can control hormone levels without medication, but requires the cat to eat nothing else
- Radioactive iodine therapy — a highly effective, one-time curative treatment available at specialist referral centres
- Surgery — thyroidectomy to remove the affected gland; curative but carries anaesthetic risk in older cats
We typically recommend starting with medication to stabilise thyroid levels and assess kidney function, then discussing longer-term options with you once we have a full clinical picture. There is no single “best” treatment — the right approach depends on your cat’s individual health profile and your circumstances.
Book a Thyroid Check for Your Cat
If your older cat is losing weight, has become restless or vocal, or is drinking more than usual, a thyroid test is a sensible first step. It’s a simple blood test — book a consultation and we’ll discuss the results with you.