Your dog's thyroid gland is located in their neck. Hypothyroidism occurs when this gland is underactive. This is often a genetic issue, so there isn’t anything you can do to prevent it.

There are a lot of symptoms to look out for with this condition as it can affect all parts of the body — but it’s important to get it treated as soon as possible before it becomes more serious. 

In this guide to hypothyroidism in dogs, you’ll learn: 

Hypothyroidism typically affects medium to large sized dogs between the ages of four and 10. It’s much rarer in toy and miniature breeds.

So, what is hypothyroidism in dogs? It often develops due to an underactive thyroid. It’s the opposite of hyperthyroidism which is when the thyroid gland is overactive. 

The thyroid gland, along with the pituitary gland, produces hormones that help to regulate the systems of the body. Hypothyroidism occurs when there is an issue with the thyroid that causes those hormones to be out of balance. 

The metabolism then slows down, affecting every organ, and causes various symptoms that are often passed off as old age, such as weight gain and lethargy as well as coat and skin issues. As symptoms of hypothyroidism in dogs can be mistaken for other conditions, it’s easy to miss. 

There are quite a few symptoms to look out for. This is because slowed metabolism affects every part of the body and so causes signs that can vary from dog to dog. 

The signs of hypothyroidism in dogs, include: 

Congenital hypothyroidism signs include:

Has your dog’s behavior suddenly changed? Are they now anxious, whining constantly, not behaving and seemingly intolerant of other dogs and people? You may be wondering what you’ve done wrong and desperately searching for training to improve this behavior — but it could all be down to a thyroid problem. 

If your dog isn’t showing any of the traditional signs of hypothyroidism and only present with behavioral problems, then it’s easy to miss. 

Humans can have changes in behavior too with hypothyroidism and with dogs this is sometimes the first and only sign. A study conducted on 1,500 dogs with behavioral problems found that 60% of them had a thyroid problem. 

Like with people, treatment can help you to see a change in your dog’s behavior too.

These are the three types of hypothyroidism and how it’s caused: 

Primary hypothyroidism: this accounts for 95% of cases and results from a problem with the thyroid gland. This is most commonly through lymphocytic thyroiditis, when the immune system attacks the thyroid. It could also be idiopathic thyroid gland atrophy, when fat tissue replaces normal thyroid tissue.

Secondary hypothyroidism: this is usually caused by a decrease in the thyroid hormone and a problem with the pituitary gland. Often this is due to an expanding tumor that destroys the hormone producing activity of the gland. 

Congenital hypothyroidism: this can be caused when the thyroid gland is underdeveloped, missing or abnormally placed. It could also be due to dwarfism, issues with iodine levels or a hormone deficiency. 

Signs of hypothyroidism can mimic other conditions, so a correct diagnosis needs to be made through careful attention to the symptoms and test results. Your veterinarian may run blood tests, serum chemistry panels, and a urinalysis to narrow down a diagnosis. 

Once hypothyroidism is suspected, a blood sample is used to measure the levels of the thyroid hormone in a total thyroxine test, or T4 concentration screening test. Low levels of thyroxine can point to hypothyroidism.

Additional tests will be performed to confirm the diagnosis. This can include further hormone testing, such as a TSH stimulation test, free T4 test, an equilibrium dialysis, and imaging of the thyroid by ultrasound, scintigraphy and sonography.

The response to a thyroid hormone supplementation can help to confirm the diagnosis. Often these tests can rule out or find other causes of the hypothyroidism, such as a tumor or an iodine issue.

Hypothyroidism is usually not a serious issue and is easy to treat, especially if caught early. However, severe hypothyroidism can lead to paralysis, hypothermia and coma. There is also a chance it has been caused by a tumor. So, although there are a lot of symptoms to look out for, it’s important to see your vet as soon as possible. 

Hypothyroidism isn’t curable, but it can be treated. Dog thyroid medication consists of a thyroxine replacement given orally for the duration of the dog’s life. This replacement starts as a standard level of the hormone, and is adjusted based on your dog’s weight. 

Initially, the supplement may be given twice a day, but will usually be adjusted to once per day. A blood sample to check your dog’s hormone levels is taken after one month of treatment. Over time, your dog’s body may become tolerant of the thyroid hormone replacement, and the dose may need to be adjusted. Generally, your dog’s hormone level should be tested every six months.

Overdosing can occur, and will need to be reported to your veterinarian so that your dog’s hormone replacement level can be adjusted. 

Symptoms of a hormone overdose can resemble that of hyperthyroidism, and can include:

If another cause for the hypothyroidism is found, such as cancer, treatment will be prescribed appropriately.

Hypothyroidism dog treatment can be done using natural remedies. This stabilizes the glands using chemical compounds found in plants. This will be via specifically formulated food or a supplement. You might want to mix this in with their regular food to start with. This is to ensure they eat it because you don’t want to make their issues worse if they refuse it.

It’ll also help to avoid gastrointestinal upset which can be caused by changing their diet too quickly. 

After a couple of weeks, your dog should be fully on their new diet and you should begin to see improvements. They may need to stay on their new diet or take the supplement for the rest of their life - although it has many benefits for them, so there is no harm in this. 

This is a much cheaper solution than drugs such as levothyroxine that can be used to regulate the thyroid. Although, it’s important to note that the drugs do work much quicker, allowing an underactive gland to return to its normal rate of hormone production almost instantly. 

You’ll also need to see the vet either way, to make sure the new diet or supplements are working and to make sure their hypothyroidism isn’t due to a tumor, for example, that won’t be cured by natural remedies.

Firstly, the vet will probably tell you to avoid processed dog food that contains high levels of carbohydrates and this food can make their issue worse. They may also suggest that you don’t feed your dog dry food or a raw food diet. 

Dogs with hypothyroidism need a healthy, balanced diet alongside their medication. Your vet will be able to advise you on the best dog food for hypothyroidism or may suggest speaking to a nutritionist.

It may be that homemade food is the best option for your dog's specific needs and they can point you in the direction of recipes. Fresh vegetables including broccoli, carrots and green beans are beneficial for their thyroid.  

Alternatively, there’s dog food specifically formulated to be both low fat and meet their nutritional needs. 

Check out our friends over at Dog Food Advisor for advice on the best food to feed your pup including the best natural dog food. 

You should start to see improvements in your dog within four to eight weeks of starting treatment.

If you notice new signs of hyperthyroidism or their existing symptoms don’t subside, talk with your veterinarian. An adjustment may be needed. 

Treatment with a thyroid hormone supplement is a lifelong therapy. Your veterinarian will schedule regular check-ups to ensure your dog receives the right level of hormone supplementation throughout their life.

Left untreated, hypothyroidism can shorten your dog’s lifespan. However, once it’s diagnosed, the treatment will enable your dog to continue living a long and healthy life. 

When your dog has a health issue, the last thing you want to be thinking about is how much it’ll cost. You just want to do all you can to help them feel better. Compare pet insurance and browse wellness plans today and you’ll have peace of mind that, if they do develop hypothyroidism, you’ll be covered.