Thyroid disease is one of the health conditions that dogs owners should know about, because it affects quality of life, and it is easier to manage when it is caught early. This guide explains what thyroid disease is, the signs to watch for, what causes it, how it is diagnosed, how it is treated, whether it can be prevented, and how to live with a dog that has it. Every suggestion here is general guidance, not a prescription for an individual dog.
This guide covers thyroid disease in dogs in full: what it is, the signs to watch for, what causes it, how it is diagnosed, how it is treated, whether it can be prevented, and how to live with a dog that has it. Every suggestion here is general guidance, not a prescription for an individual dog, and a dog with thyroid disease should be checked by a vet, because the right treatment depends on the individual dog, its age, and how advanced the condition is.
What is thyroid disease in dogs?
Thyroid disease is a condition where the thyroid gland — a small gland in the neck that controls how fast the body burns energy — makes too much or too little thyroid hormone. In dogs, the usual problem is too little hormone, called hypothyroidism, which slows the body down: the dog gains weight, becomes lethargic, and loses hair. In cats, the usual problem is too much hormone, called hyperthyroidism, which speeds the body up: the dog loses weight despite a big appetite, becomes restless, and drinks and urinates more. Thyroid disease is common, and it is diagnosed with a blood test and treated with medicine.
The rest of this guide covers the signs, the causes, how thyroid disease is diagnosed, how it is treated, whether it can be prevented, and how to live with a dog that has it. A dog with thyroid disease should be checked by a vet, because the right treatment depends on the individual dog, its age, and how advanced the condition is — and because some of the signs of thyroid disease can also be signs of other conditions, which need a vet to tell apart. The dog ideal weight calculator works out a target weight range, and the when is a dog considered a senior guide gives the senior thresholds by size.
Signs of thyroid disease in dogs
The signs of thyroid disease in dogs are listed below. Not every dog with thyroid disease will show every sign, and some dogs will show only one or two — but any one of these signs, especially if it lasts more than a few days or gets worse, is worth mentioning to a vet. A dog that is bright, eating, drinking, and otherwise well between episodes is less likely to be seriously ill than a dog that is lethargic, off its food, or losing weight — but the only way to know is to check.
- In dogs: weight gain, even though the dog is not eating more.
- In dogs: lethargy, and a dog that seems tired, dull, or cold.
- In dogs: hair loss, a dull coat, and skin problems.
- In cats: weight loss, even though the dog is eating more than usual.
- In cats: restlessness, hyperactivity, and a dog that is always hungry.
- In cats: drinking and urinating much more than usual.
- In both: a dull coat, and a dog that seems generally unwell.
If two or more of those signs apply, or if one sign is severe — a dog that cannot urinate, cannot breathe, cannot stand, or has had a seizure lasting more than five minutes — see a vet the same day. Those are signs that need a vet, not waiting. Bring a note of when the signs started, how often they happen, and what the dog eats and drinks — that information helps the vet far more than a guess about the cause. The how to tell if your dog is overweight guide gives the hands-on check for weight, which matters for many of these conditions.
Causes and risk factors for thyroid disease
In dogs, hypothyroidism is usually caused by the immune system attacking the thyroid gland, so it makes less and less hormone over time. It is more common in middle-aged dogs and in some breeds. In cats, hyperthyroidism is usually caused by a benign growth on the thyroid gland, so it makes more and more hormone, and it is most common in older cats. Some medicines can affect the thyroid, and some other conditions can look like thyroid disease, which is why a blood test is needed to diagnose it — the signs alone are not enough.
Some dogs are more prone to thyroid disease than others, because of their genes, their breed, their size, or their age — but breed and age are not destiny, and a dog of any breed can develop thyroid disease. What an owner can control is weight, food, exercise, and vet checks: a dog at a healthy weight, with measured food and daily exercise, is less likely to develop thyroid disease and will cope better with it if it does. A dog that is overweight, that eats a poor diet, or that never sees a vet is more likely to develop thyroid disease and to have it found late, when it is harder to treat.
How thyroid disease is diagnosed
A vet diagnoses thyroid disease with a blood test, which measures the thyroid hormone and the hormone that controls it. The vet may also check the kidneys, the liver, and the heart, because thyroid disease affects them all. A dog that is gaining weight and lethargic, or losing weight despite a big appetite, should be checked promptly — thyroid disease is easy to diagnose and easy to treat, and a dog that is left untreated will get worse over time.
If you are worried about your dog, see a vet and mention thyroid disease by name, with the signs you have seen and when they started. Bring a note of what the dog eats, how much, and any medicines it takes, and whether it has had thyroid disease or a related condition before. A video of the signs, if it is safe to take one, helps the vet far more than a description — especially for seizures, limping, or breathing problems. Do not try to diagnose thyroid disease yourself, and do not buy medicines or special diets for it without veterinary advice, because the wrong treatment can make it worse.
Treatment and management of thyroid disease
Treatment is medicine, prescribed by the vet, and it is usually for life. A dog with too little hormone needs a daily thyroid supplement, and a cat with too much hormone needs a daily medicine to slow the thyroid down — or, in some cases, a special diet, surgery, or a treatment with radioactive iodine, which the vet will discuss. The dose is set by regular blood tests, and it must be given every day, at the same times. Do not stop the medicine without veterinary advice, because the signs will come back. With the right dose, a dog with thyroid disease is bright, active, and well.
Treatment is a decision made with the vet, weighing the dog's age, health, and quality of life against the treatment and its side effects. Some owners choose not to treat, and to keep the dog comfortable instead — and that is a valid choice, made with the vet, not on the basis of a web page. Whatever is decided, the treatment must be followed every day, at the same times, and the dog must be checked regularly, because thyroid disease changes over time, and the treatment needs to change with it. Do not stop a medicine suddenly, and do not change the dose without veterinary advice.
Living with a dog with thyroid disease
A dog with thyroid disease can live a full and happy life with the right care, but it needs a routine: medicine every day at the same times, regular vet checks with blood tests, and a monthly weigh-in. The owner must watch weight, appetite, drinking, and energy, and mention any change to the vet promptly, because a change may mean the dose needs adjusting. A dog with thyroid disease that is well managed is bright, active, and well — and a dog whose dose is wrong will be lethargic or restless, so the blood tests matter.
Keep a routine: the same times for food, medicines, walks, and play, the same places for furniture, food, and water, and a calm, predictable home. Keep a note of appetite, drinking, weight, and behaviour, and mention any change to the vet promptly — a change that lasts more than a few days, or that gets worse, is worth a vet visit. Keep the dog at a healthy weight, with measured food and daily exercise at a level that suits its body, and keep vet checks regular: once a year as an adult, and twice a year as a senior. The senior dog diet guide covers feeding older dogs, and the dog calorie calculator works out daily calories for any weight.
Can thyroid disease be prevented?
Thyroid disease cannot be prevented, because it is about genes and age — but it can be found early, and early treatment works best. Have the dog checked regularly as it gets older, with blood tests, so thyroid disease is found before it causes serious problems. Mention any change in weight, appetite, drinking, or energy to the vet promptly, because those are the first signs, and they are easy to miss if the dog is not weighed monthly.
Early checks matter most: have the dog checked regularly, so thyroid disease is found early, when treatment works best. Keep the dog at a healthy weight, with measured food and daily exercise, and mention any change in drinking, eating, weight, or behaviour to your vet early, because a change caught early is easier to treat than one left for weeks.
For related reading, see the dog ideal weight calculator, the dog body condition score chart, the how to tell if your dog is overweight guide, the senior dog diet guide, the dog calorie calculator, the when is a dog considered a senior guide.
Frequently asked questions
What is thyroid disease in dogs?
Thyroid disease is a condition where the thyroid gland — a small gland in the neck that controls how fast the body burns energy — makes too much or too little thyroid hormone. In dogs, the usual problem is too little hormone, called hypothyroidism, which slows the body down: the dog gains weight, becomes lethargic, and loses hair. In cats, the usual problem is too much hormone, called hyperthyroidism, which speeds the body up: the dog loses weight despite a big appetite, becomes restless, and drinks and urinates more. Thyroid disease is common, and it is diagnosed with a blood test and treated with medicine.
What are the signs of thyroid disease in dogs?
The most common signs are: In dogs: weight gain, even though the dog is not eating more. In dogs: lethargy, and a dog that seems tired, dull, or cold. In dogs: hair loss, a dull coat, and skin problems. See the full list above for every sign to watch for, and see a vet promptly if two or more apply, or if one sign is severe.
What causes thyroid disease in dogs?
In dogs, hypothyroidism is usually caused by the immune system attacking the thyroid gland, so it makes less and less hormone over time. It is more common in middle-aged dogs and in some breeds. In cats, hyperthyroidism is usually caused by a benign growth on the thyroid gland, so it makes more and more hormone, and it is most common in older cats. Some medicines can affect the thyroid, and some other conditions can look like thyroid disease, which is why a blood test is needed to diagnose it — the signs alone are not enough.
How is thyroid disease diagnosed?
A vet diagnoses thyroid disease with a blood test, which measures the thyroid hormone and the hormone that controls it. The vet may also check the kidneys, the liver, and the heart, because thyroid disease affects them all. A dog that is gaining weight and lethargic, or losing weight despite a big appetite, should be checked promptly — thyroid disease is easy to diagnose and easy to treat, and a dog that is left untreated will get worse over time.
How is thyroid disease treated?
Treatment is medicine, prescribed by the vet, and it is usually for life. A dog with too little hormone needs a daily thyroid supplement, and a cat with too much hormone needs a daily medicine to slow the thyroid down — or, in some cases, a special diet, surgery, or a treatment with radioactive iodine, which the vet will discuss. The dose is set by regular blood tests, and it must be given every day, at the same times. Do not stop the medicine without veterinary advice, because the signs will come back. With the right dose, a dog with thyroid disease is bright, active, and well.
When should a dog with thyroid disease see a vet?
See a vet promptly if the dog shows any of the signs above, especially if they last more than a few days or get worse — and the same day if the dog cannot urinate, cannot breathe, cannot stand, has had a seizure lasting more than five minutes, or is lethargic or off its food. Bring a note of when the signs started and what the dog eats and drinks. A dog with thyroid disease should be checked by a vet, because the right treatment depends on the individual dog, its age, and how advanced the condition is.
Results on this page are estimates for general information only and are not veterinary advice. If your pet is ill, underweight, overweight, pregnant, or has a health condition, consult your veterinarian before changing diet or care.