Hyperthyroidism in Cats: Signs, Diagnosis and Treatment Options
An older cat that eats like a teenager but keeps getting thinner is a classic picture of hyperthyroidism. It is one of the most common hormonal disorders in cats, and, with treatment, most cats do very well.
What happens in the body
The thyroid glands in the neck produce hormones that regulate metabolism. In hyperthyroid cats, usually because of a benign tumor of the gland, the thyroid makes too much hormone. This speeds up the metabolism of every organ, stressing the heart, kidneys and other systems.
The disease is typically seen in cats older than ten. It is rare in cats under six.
Signs
- Weight loss despite a good or ravenous appetite
- Increased thirst and urination
- Restlessness, hyperactivity or irritability
- Vomiting or diarrhea
- A rough, unkempt or greasy coat
- Rapid heartbeat, panting or breathing trouble
- Heavy, large stools
- A lump in the neck, in some cats
- Night-time yowling
Some cats show few signs at first, and owners may think the cat is just active for its age. See the senior cat care guide. Signs like open-mouth breathing are an emergency. See the emergency warning signs guide.
Diagnosis
Your vet will:
- Examine your cat and feel the neck
- Measure blood total T4, and sometimes free T4 or other thyroid tests
- Run blood and urine tests to look at kidneys, liver and other organs
- Check blood pressure
- Listen to the heart and sometimes do an ultrasound of the heart
Because hyperthyroidism can hide kidney disease, assessing the kidneys is vital before and after treatment. See chronic kidney disease in cats.
Treatment options
Medication. Daily tablets or a transdermal gel applied to the ear reduce hormone production. They are effective and reversible, but need lifelong treatment and regular blood tests. See how to give a cat a pill.
Prescription diet. An iodine-restricted diet can control the disease in some cats, but the cat must eat nothing else, including treats and food from other pets.
Radioactive iodine therapy. A single injection destroys the overactive tissue and cures most cats. It requires a stay in a licensed facility for several days and is usually the most effective option. It can be costly.
Surgery. Removal of the affected thyroid lobe can cure the disease, but needs a stable cat and carries anesthetic risk, as well as the risk of damaging nearby glands.
The best choice depends on your cat's age, health, kidney function and your finances and lifestyle. See cat vet visit costs, and use the US vet directory to find a vet, or a facility offering radioiodine.
Monitoring
After starting treatment, your vet will recheck thyroid hormone, kidney values and blood pressure within weeks, and then every few months. Doses may need adjusting. Report vomiting, lethargy or appetite loss, which can be side effects of medication.
Complications
Untreated hyperthyroidism can cause:
- Heart disease, such as thickened heart muscle and heart failure
- High blood pressure, which can lead to blindness and kidney damage
- Severe weight loss and muscle wasting
- Hyperactivity and exhaustion
Treating the disease early prevents many of these complications.
Hyperthyroidism and kidney disease
About a fifth to a third of hyperthyroid cats also have kidney disease. Excess thyroid hormone increases blood flow through the kidneys and can mask the problem. After treatment, kidney values may rise. Your vet may trial medication first to see how the kidneys respond.
Home care
- Feed a balanced diet, and measure portions. See how much should I feed my cat.
- Weigh your cat regularly.
- Provide quiet places to rest.
- Keep a diary of appetite, thirst and behavior.
- Stay on schedule with medication and recheck visits.
Choosing a treatment
There is no single best option for every cat. Radioiodine is often the first choice for cats that are healthy enough and for owners who can afford it, since it usually cures the disease without daily medication. Medication is a good starting point when kidney function is uncertain, because it can be adjusted or stopped. Diet suits cats that eat well, live alone and will accept a single food. Surgery is less common, but suits some cats. Talk through each option with your vet, along with cost, travel and your cat's temperament.
Signs of improvement
After treatment begins, many owners notice a calmer cat within a few weeks, along with steadier weight, a softer coat and less vomiting. Keep a record of weight and appetite so your vet can see the trend.
Helping an anxious, hungry cat
Hyperthyroid cats are often noisy and demanding at mealtimes. Feed small, frequent meals, use puzzle feeders to slow eating and keep calm routines. Never cut calories to stop the weight loss, since the cat needs extra energy until treatment takes effect.
Prognosis
Most cats treated early live for years and regain weight and energy. Cats with severe heart or kidney disease do less well. Regular monitoring is the key.
Frequently asked questions
What causes hyperthyroidism in cats?
Usually a benign growth on the thyroid gland that produces too much hormone. The exact cause is not known.
Can it be cured?
Radioactive iodine therapy and surgery can cure many cats, while medication and diet control it.
Is hyperthyroidism dangerous?
Yes. Untreated, it damages the heart, raises blood pressure and can be fatal.
Why is my cat hungry but losing weight?
Excess thyroid hormone speeds up metabolism, so cats burn calories faster than they take them in.
Sources and further reading
Health information changes as research does. These organizations publish guidance worth reading alongside our articles.
- CDC Healthy Pets, Healthy PeoplePublic-health advice on pets, zoonotic disease and safe handling.
- American Animal Hospital AssociationAccreditation body and practice guidelines for companion-animal hospitals.
- WSAVA Global GuidelinesGlobal vaccination, nutrition and pain guidelines for small-animal vets.
Tailwisp is independent and written under our editorial policy. Learn who we are, or browse all cat guides.
This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.