How to treat your hypothyroid dog

Most humans who have hypothyroid disease are all too familiar with a sometimes overwhelming sense of fatigue, when the only strength that can be mustered is to plop down on the couch and wearily lift the remote. What if your pooch is a chronic couch potato, too? Could he also have this disease?

There’s actually a good chance he could. Hypothyroidism is the most common hormone deficiency in dogs, according to Ron Hines, DVM on It occurs when the thyroid gland – two small lobes in your dog’s neck – is underactive and fails to secrete sufficient amounts of the hormone thyroxine. This affects your dog’s metabolism, causing him to slow down. (Hypothyroidism is the opposite of hyperthyroidism, which occurs when the thyroid overproduces thyroid hormone, making your dog, well, very hyper.)

What are the Symptoms of Hypothyroidism?

Hypothyroidism may have multiple symptoms, since every cell in your dog’s body can be affected by reduced levels of thyroid hormone. Peteducation, thyroid-info and marvistavet list these symptoms as the most common:

  •   Lethargy – Your dog isn’t interested in playing, takes frequent naps and gets tired on long walks
  •   Weight gain – Your dog may put on pounds although his appetite hasn’t increased
  •   Dry, flaky skin and bacterial skin infections
  •   Thickening of the facial skin (called “myxedema”), leading to more skin folds
  •   Hair loss, especially on the tail, creating a “rat tail” appearance
  •   Intolerance to cold – Your dog looks for warm places to lie down
  •   Slow heart rate
  •   Anemia and/or high cholesterol
  •   Frequent ear infections
  •   Extreme behavioral changes such as unprovoked aggression, head tilting, seizures, anxiety or compulsivity

What Causes Hypothyroidism?

In dogs, the thyroid exists as two separate halves. It produces two forms of thyroid hormone, called T3 and T4. T3 is the active form of the hormone. T4 is the inactive form that is created to circulate in the bloodstream; it’s converted into T3 when it is absorbed into tissue cells. In dogs, about half of the T3 comes from the thyroid gland, reports The remaining T3 comes from the body’s other tissues. (In humans, 80 percent of T3 comes from our body’s other tissues.)

T4 production is controlled by the pituitary gland at the base of your dog’s brain. The pituitary gland produces TSH (thyroid stimulating hormone), which stimulates the thyroid gland to produce more T4 when levels drop. Hypothyroidism in dogs is typically caused by autoimmune thyroiditis, which means a dog’s own immune system is attacking the tissues of his thyroid gland, according to hypothyroidism expert Mary Shoman on

“The dog’s own system attempts to compensate for this at first by secreting more and more of the thyroid hormone, but eventually the gland is unable to keep up with the attacks on its tissue, and the dog becomes hypothyroid and symptomatic,” Shoman writes. “While there is a genetic predisposition for thyroid disorders, environmental factors such as pollutants and allergies probably play a role as well.”Less commonly, canine hypothyroidism can be caused by natural atrophy of the thyroid gland, dietary iodine deficiency, or a congenital problem, reports dogs become hypothyroid in midlife, between the ages of 4 and 10. It affects male and female dogs equally.

Medium- to large-sized breeds are more susceptible to the disease. According to, some breeds with a definite predisposition to develop hypothyroidism are Doberman Pinschers, Golden Retrievers, Irish Setters, Great Danes, Dachshunds and Boxers. Hypothyroidism rarely occurs in toy and miniature breeds.

How is Hypothyroidism Diagnosed?

Your vet will examine your dog and, if hypothyroidism is suspected, a urinalysis and the following blood tests may be performed:

  •   Baseline T4 or Total T4 (TT4) – The most common test for hypothyroidism. A lowered level of the T4 hormone is an indication that the thyroid is underactive. Since other conditions and medications may cause a low T4 level – for example, dogs on antibiotics or heart medication may have low T4 levels, but are not actually hypothyroid – your vet may perform additional tests.
  •   Baseline TSH – This test measures the level of thyroid stimulating hormone. In combination with T4 or T3, it provides a clearer indication of your dog’s thyroid activity.
  •   Baseline T3 – Although T3 is the active thyroid hormone, its level can fluctuate into the normal range in hypothyroid dogs, according to Therefore this test is only reliable when it’s used in combination with the T4 or TSH tests.

How is Hypothyroidism Treated?

As with humans, hypothyroidism can be easily treated by taking a “thyroid pill” every day that contains a synthetic version (called levothyroxine) of the deficient hormone. You should notice an improvement in your dog within a few months of starting him on the medication.

According to pet education, your dog will initially be placed on the standard dose for his weight, and then your vet will periodically draw blood samples to ensure the dosage is sufficient. If you notice your dog showing hypothyroidism symptoms while he is on the medication, you should take him to the vet for blood work.

Your dog will need to take the medication for the rest of his life…which, with this simple treatment, should be long and symptom-free.

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