Cat thyroid problems: yowling at night, eating more, losing weight

It's 3 a.m. and your older cat is wailing in the hallway. During the day they eat everything in sight, yet they're getting thinner. It's tempting to put it down to old age or bad manners. But these are classic signs of an overactive thyroid (hyperthyroidism), and it's one of the most treatable problems in older cats.

What is hyperthyroidism?

The thyroid glands sit in the neck and produce hormones that control the body's metabolism. In hyperthyroidism, the glands make too much hormone, almost always because of a benign (non-cancerous) growth. The body goes into overdrive: the heart beats faster, energy is burnt too quickly, and many organs are affected.

It is the most common hormone (endocrine) disease in cats, and mostly affects cats over 8 to 10 years old. It's reported in around 1 in 10 cats older than ten.

The signs

Signs usually start subtly and get worse over weeks or months:

• weight loss despite eating more, which is the most common sign
• a huge appetite, begging, stealing food
• drinking and peeing more
• restlessness, hyperactivity or anxiety
• vomiting or diarrhoea
• a scruffy, greasy or matted coat
• a fast heart rate, sometimes faster breathing
• more vocalising: loud meowing or yowling, often at night

Why the night-time yowling?

Many owners first notice the noise: an older cat who suddenly yowls in the night, often loudly and persistently. It's thought to come from the restlessness and "overdrive" the extra hormone causes. But yowling in an older cat can have other causes too: high blood pressure, cognitive changes (a form of feline dementia), hearing loss, pain, or simply wanting attention. So it's always worth a vet check rather than guessing.

Why it matters: the complications

Left untreated, hyperthyroidism can lead to:

• heart disease, because the heart is working too hard for too long;
• high blood pressure, which can damage the eyes (including sudden blindness from retinal detachment), the kidneys and the brain;
• severe weight and muscle loss.

The good news: treated early, most of these can be prevented.

How it's diagnosed

Usually with a simple blood test measuring thyroid hormone (total T4). In some cats, especially early cases or cats with other illnesses, the result can be borderline and your vet may run extra tests (such as free T4). Your vet will usually also check blood pressure, the kidneys and the heart.

Why the kidneys matter: an overactive thyroid increases blood flow through the kidneys and can hide kidney disease. When the thyroid is brought under control, a kidney problem that was already there may appear. That's why vets monitor kidney values before and during treatment, and often start with tablets to see how the kidneys respond.

The four treatment options

Treatment	How it works	Good to know
Tablets (methimazole / thiamazole)	Blocks thyroid hormone production	Given daily for life. Also available as a gel rubbed on the inside of the ear, for cats who won't take pills. Needs regular blood tests
Iodine-restricted diet	The thyroid needs iodine to make hormone	The cat must eat only this food, which is difficult in multi-cat homes or for cats who go outdoors
Surgery	Removes the affected thyroid gland(s)	Needs a general anaesthetic, which carries more risk in older cats with heart or kidney problems
Radioactive iodine (I-131)	A single injection destroys the abnormal thyroid tissue	Cures more than 90% of cats with one treatment. Only available at specialist centres, and the cat stays in hospital for some days while it's temporarily radioactive

Your vet will help you choose based on your cat's age, other health problems, temperament and what's available where you live. Many cats start on tablets first, even when another treatment is planned.

Living with a hyperthyroid cat

• Give medication exactly as prescribed, and keep the check-ups: blood tests tell your vet whether the dose is right.
• Weigh your cat regularly. Weight gain back to normal is a great sign.
• Watch for side effects of tablets (loss of appetite, vomiting, itchy face) and tell your vet.
• Wash your hands after giving tablets or ear gel.

With treatment, most cats go back to their old selves: calmer, a healthier weight, a better coat, and, in many homes, quieter nights. The outlook for treated cats is good.

If your older cat is losing weight or yowling at night, book a vet check. It's one of the most rewarding problems to diagnose.