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Hypothyroidism In Dogs

Hypothyroidism is an endocrine disorder where the thyroid glands do not function properly.

The thyroid glands are in charge of producing the hormones thyronine (T3) and thyroxine (T3) and calcitonin. The hormones T3 and T4 regulate metabolism.

Dogs with hypothyroidism have decreased levels of either T3 or T4, or both. Hypothyroidism is often suspected in dogs that have trouble with weight gain or obesity and suffer from hair loss and skin problems.

The causes of canine hypothyroidism include congenital disease, iodine deficiency, cancer and medical treatment (iatrogenic).

Symptoms of Hypothyroidism In Dogs

Tired dog laying on a pillowThe most common symptoms of hypothyroidism in dogs are the following:

  • Lethargy
  • Generalized weakness
  • Dry hair coat
  • Decreased Heart Rate
  • Excessive scaling
  • Fat deposits in eyes
  • Recurring skin infections
  • Intolerance to cold
  • Exercise intolerance
  • Mental dullness
  • Unexplained weight gain
  • Hair loss (alopecia)
  • Excessive hair shedding
  • Poor hair growth

Causes of Hypothyroidism in Dogs

It can be difficult to pinpoint the cause of hyperthyroidism. However, hypothyroidism is usually caused by one of the following:

Lymphocytic Thyroiditis

Lymphocytic thyroiditis is the most common cause of hypothyroidism and is generally thought to be an autoimmune disease. This disease occurs when either there is an inflammation of the thyroid (thyroiditis) or the dog’s body thinks that the thyroid gland either foreign or abnormal and thus attacks it.

Congenital Hypothyroidism

Congenital hypothyroidism is less common but usually occurs in puppies that have an underdeveloped thyroid.

Cushing’s Disease

Cushing’s disease can also cause hypothyroidism due to the imbalance of thyroid levels.


A poor diet that lacks the proper nutrients can also lead to hypothyroidism because a dog is getting extra additives that the dog’s body will reject.

Weight gain and lack of exercise can also be contributing factors.


Your dog’s environment including too much exposure to toxins, over-vaccinating a dog and even some steroids can contribute to thyroid issues.

Cancer of the Thyroid Gland

Although rare, cancer of the thyroid gland can also lead to hypothyroidism.

Breeds Most Affected by Hypothyroidism

Hypothyroidism is more common in medium to large-sized dogs of 4 to 10 years of age.

The following breeds are more pre-disposed to the condition:

Diagnosis of Hypothyroidism

Your vet will usually perform a few tests to see if your dog has developed hypothyroidism.

The most common test is a screening to check the total Thyroxin levels which is done through blood work to test the thyroid levels.  If your dog has a lower level of Thyroxin, this usually indicates hypothyroidism.

Your vet may also want to do a urinalysis and complete blood work to make sure there aren’t any other conditions or illnesses.

X-rays and diagnostic scans can help determine if there any thyroid tumors causing the hypothyroidism.  If tumors are present, surgery or radiation might be necessary if the tumors are malignant and/or causing the hypothyroidism.

Treatment of Hypothyroidism

Hypothyroidism is treatable, but not curable and requires life-long treatment with hormones and dietary restrictions at home.

Your vet will prescribe a type of thyroid replacement hormone based on the dog’s size and weight.

After a month or so of treatment, the vet will take a blood sample to make sure that your dog is getting the right dosage.

Your dog will be on the prescribed medication for the duration of your dog’s life.

Most clinical symptoms will be resolved after a few months.


The best way to prevent your dog from developing hypothyroidism is to feed your dog a properly balanced diet and to keep your dog’s weight under control.   Exercise, of course, helps as well.

Genetics does play a big factor but a lot is to be said of keeping your dog lean.

Can Pet Insurance Help with Hypothyroidism?

If your dog has hypothyroidism, pet insurance can help with the costs of the consistent testing that needs to occur and well as the prescribed medication.

But, pet insurance will only cover the condition if it isn’t pre-existing and you are already signed up with a plan.

This is exactly why it’s best to insure your dogs’ when they are young and before any new conditions occur.

With pet insurance plans saving you anywhere from 70% to 90% of the treatment and testing costs for the duration of your dog’s life, that can really add up in the long run!

Plans like Healthy Paws and Embrace will help you with the costs of long term illnesses like hypothyroidism which can be very helpful.

Living and Management

Dogs with hypothyroidism can live long, healthy lives as long as you keep your dog on the prescribed medication and are diligent with the follow-up vet visits.

Blood work is very important because too much or too little of the thyroid medication can be dangerous to your dog.

Otherwise, your dog can still thrive and live a happy life.

If you want to learn more about other possible health problems that might occur with your dog, our dog health glossary is a great place to start!

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