Hypothyroidism in Labrador Retrievers


Hypothyroidism in Labrador Retrievers is a condition in which the thyroid gland doesn’t produce enough thyroid hormone. It is also known as thyroid hormone deficiency as it arises when the body doesn’t produce enough of the thyroid hormone T4.

The thyroid produces two forms of the hormone, T4 (Thyroxin) and T3 (tri-iodothyronine). T3 is the active form of the hormone, responsible for maintaining the body’s metabolism. T4 is the inactive or free form of the hormone that circulates in the bloodstream. It is converted by the liver and kidneys into T3 when the body needs it. Hypothyroidism in Labrador Retrievers occurs when the thyroid gland doesn’t produce enough T4. So the bloodstream doesn’t contain enough for conversion to T3.


The most common symptoms are hair loss, weight gain, lethargy, a dull coat and intolerance to cold. Hypothyroidism is a very common condition in dogs. But is easily treatable with hormone replacement therapy in the form of an oral medication called Levothyroxine.

If Your Labrador has hypothyroidism and your vet proscribes Levothyroxine, he’ll likely need to take it for the rest of his life. And have periodic blood tests to measure thyroid hormone levels. The good news, however, is that the condition isn’t life-threatening. And as long as the correct dosage of Levothyroxine is administered you’ll see relief of the symptoms. Your Labrador can continue to live a normal and healthy life!

How Do Labradors Get Hypothyroidism?

About 95% of hypothyroidism cases in dogs are caused by one of two conditions. Lymphocytic thyroiditis or idiopathic thyroid gland atrophy. That is the inflammation or shrinking of the thryoid gland. In either case, the thyroid gland is eventually unable to produce sufficient levels of the thyroid hormone.

Other far less common causes of the condition include failure of the pituitary gland to produce sufficient TSH (the thyroid stimulating hormone). And then there are congenital birth defects in the thyroid gland, or cancer of the thyroid gland.

Signs of Hypothyroidism in Labrador Retrievers

Common symptoms include unexplained weight gain, lethargy, dry or lusterless coat. Also recurring skin, toenail, and ear infections, excessive shedding or hair loss, and intolerance to cold. Less common symptoms include seizures and infertility.


In order to determine whether or not your Labrador has hypothyroidism, your vet will first perform a thorough physical exam. Diagnosing the condition can sometimes be challenging because the symptoms associated with it can also be caused by other medical conditions, so you’ll want to provide your vet with as much information as you can about the history of symptoms.

Keep in mind, for instance, that certain symptoms of hypothyroidism can also be symptomatic of other conditions like inhalant allergies. However, in hypothyroid Labradors, unlike allergic Labradors, skin will not appear red or inflamed. If hypothyroidism is a possible cause of your Labrador’s symptoms, your vet will perform a series of routine lab tests.

The biochemical profile of your dog

The biochemical profile looks at the function of internal organs and the levels of enzymes circulating in the blood. Low levels of certain enzymes like glucose, sodium, and potassium can be possible indicators of hypothyroidism.

The biochemical profile will also tell your vet if your Labrador’s blood contains high cholesterol levels. This can also point to hypothyroidism because the thyroid hormone is partially responsible for the breakdown of fats in the body. High cholesterol is seen in approximately 75% of dogs diagnosed with hypothyroidism.

Your dog’s blood count

A complete blood count, or CBC, looks at the levels of white blood cells, red blood cells, and platelets in your Labrador’s blood. A decreased red blood cell count (anemia) can indicate possible hypothyroidism. This is because the thyroid gland is partially responsible for maintaining an optimal red blood cell level. A decreased function of the immune system can also be symptomatic of hypothyroidism. So your Labrador’s blood might show high white blood cell counts, which increase to fight infection or illness.

Your vet might also perform a urinalysis on your Labrador. It’s important to make sure that your Labrador’s illness isn’t the result of a urinary tract infection. If any of the preliminary tests show signs of hypothyroidism, your vet will perform other diagnostic tests as well.

Specific tests

One of the clearest indicators of hypothyroidism is a low level of T4 in the blood. Remember that the thyroid gland produces more T4 than T3. And a certain amount of “free” T4 circulates in the blood to be converted into T3 when the body needs it. A free test measures the amount of available T4 in the bloodstream, and can diagnose hypothyroidism in your Labrador.

If T4 levels are low, your vet will likely send the blood samples to a referral laboratory for further analysis. Specifically to check TSH levels. Since the pituitary gland stimulates the production of T4, when T4 levels drop significantly, the pituitary gland will try to produce more TSH to stimulate T4 production. So a dog with hypothyroidism might show higher levels of TSH.

The Labrador Handbook by Pippa Mattinson

How Is Hypothyroidism in Labrador Retrievers Treated?

Treating hypothyroidism in your Labrador is relatively simple. Your vet can proscribe hormone replacement therapy in the form of an oral drug called Levothyroxine. Levothyroxine is a synthetic form of thyroxin (T4), which when administered will regulate the level of this hormone in your Labrador’s blood because the thyroid can’t produce enough of it. When administered, Levothyroxine will work to restore normal metabolism in the body.

Does Levothyroxine Have Any Side Effects?

If given a correct dosage, your Labrador should tolerate Levothyroxine relatively well. As with all medications, however, some dogs can develop a rare allergic reaction. Symptoms include inflammation, vomiting, and diarrhea. Contact your vet immediately if your Labrador appears ill after taking Levothyroxine. The drug is also not recommended for dogs with hypertension (high blood pressure), heart disease, diabetes, or Addison’s disease.

The Labrador Site Founder

Pippa Mattinson is the best selling author of The Happy Puppy Handbook, the Labrador Handbook, Choosing The Perfect Puppy, and Total Recall.

She is also the founder of the Gundog Trust and the Dogsnet Online Training Program 

Pippa's online training courses were launched in 2019 and you can find the latest course dates on the Dogsnet website