Thyroid Problems in Dogs: What You Need to Know

Thyroid conditions are not uncommon, so it’s important to know the symptoms and the types of tests used to diagnose thyroid problems in dogs.

Thyroid problems can affect any dog. By: Geoff Stearns

There are many health conditions that can affect dogs, but thyroid problems are among the more common ailments.

Imagine your dog has started drinking water more often, going outside frequently to urinate, or starts eating more food yet loses weight.

While these symptoms can be signs of quite a few disorders, it’s important to consider thyroid problems in dogs.


What Is a Thyroid?

The thyroid is a small gland in the throat.

The hormones produced by this gland regulate several bodily processes, and changes in the amount of hormones produced can create endocrine conditions in dogs. You may be aware of these conditions because they also affect humans. I know this because they also affect me.

I was a teenager when the problems started. My heart rate would elevate, I would get hot often and it was difficult to stop my mind from racing — and a miracle if I ever slept through the night.

I kept attributing it to stress until one day when I became so hot that the air conditioning was at 50 degrees and I was still sweating. I knew something was wrong. After a few tests, the doctors found that my thyroid was producing hormones at a ridiculous rate — so high that I was whisked into surgery to remove the gland.

Much like my attributing the symptoms to stress or dismissing them for some other reason, dogs may hide their discomfort until the symptoms escalate. At the time, I didn’t know what was wrong with me, and you may not know what is wrong with your dog despite some changes.

There is no one definitive cause for thyroid problems, but there are some common symptoms.

Symptoms of Thyroid Conditions

Before we explain the symptoms of thyroid conditions, it’s important to know the two main types of thyroid problems, which may or may not be accompanied by cancerous growths called carcinomas. The two main types:

  1. Hyperthyroidism occurs when the thyroid gland is producing too much thyroid hormone.
  2. Hypothyroidism occurs when the gland is not producing enough hormones to sustain a normal level of activity.

Although many of the symptoms can indicate other conditions, as a dog owner you need to be aware of them. Thyroid conditions are more common in dogs age 5 and older, though they can affect any dog, regardless of sex.

Dog thyroid gland illustration

HYPOthyroidism: Thyroid Hormone Deficiency (Most Common)

  • Weight gain
  • Dry or sensitive skin, sores
  • Shedding or hair loss
  • Lethargy
  • Sensitivity to cold
  • Decreased heart rate
  • Weakness (muscle or overall)
  • Secondary infections (eye, ear)


Thyroid Tumors: Additional Symptoms if a Tumor Is Present

  • Coughing
  • Hoarseness
  • Noticeable change in bark
  • Round mass protruding from the throat area
  • Decreased appetite
HYPERthyroidism: Excess Hormones (Rare)

  • Weight loss
  • Increased appetite or eating fast
  • Frequent urination
  • Excessive thirst
  • Heart rate elevation
  • Vomiting/diarrhea
  • Difficulty breathing
  • Enlarged thyroid or bulge in the throat
  • Nausea
  • Hyper or overactive behavior, restlessness
  • Coat dullness

Some of these symptoms may appear immediately. Others, such as coat dullness, will build up over time.

It’s important to know your pet’s routine and habits so you can identify a change. Treating a condition as soon as possible typically gives your dog a better chance of recovery. This is important for thyroid conditions because leaving them untreated may be fatal.

Your veterinarian will perform tests to evaluate the hormone levels.

Your vet may run several tests to diagnose a thyroid condition. By: Tony Alter

To diagnose thyroid conditions in your dog, many tests may be performed together or independently by your vet.

Tests to determine the level of thyroid hormone are the most common, but others may be necessary to evaluate tumors or abnormal thyroid tissues.

  • Evaluation: Tests may be performed to rule out other conditions. These may include a complete blood count (CBC), chemistry profile or urinalysis (or a combination of all three).
  • Thyroid Imaging or Scanning: X-rays and diagnostic tests help locate thyroid tissue and tumors to determine the extent of the affected area. These tests may confirm the diagnosis and pinpoint the areas needing treatment.
  • Biopsy: This will depend on your pet’s condition and the location and size of a tumor — plus the risk of hemorrhage.

Hormone Tests

  • Total T3: This test measures T3 levels but can be influenced by other factors. It is generally included in a complete thyroid profile.
  • Total T4: Thyroxine is measured using this test. Other conditions, age differences, drugs, or the size and breed of the dog can cause changes in T4 levels.
  • Free T4: This test is considered a more accurate indicator of thyroid activity; it measures the miniscule amount of total T4 that can enter the tissues. Dogs may have a low or high total T4 but a normal free T4, so it’s important to run this test in addition to the others.
  • TSH: Thyroid-stimulating hormones are measured by this test, but it has a high probability of inaccurate results (false positives, false negatives). A high or low TSH concentration cannot indicate a thyroid condition alone, so other tests are typically run (such as the ones above).


Thyroid conditions can be treated and managed. The course of treatment will depend on the test results and the recommendations of your veterinarian. Dietary changes may also be directed but should be done only in consultation with your vet.


This condition occurs when the thyroid levels are too low. The missing hormones are replaced with a synthetic supplement such as levothyroxine. In the event of removal of the thyroid gland, this supplement will replace the thyroid hormone that the body can no longer produce. (This is the same medication I have taken since my thyroid was removed.) Levothyroxine is generally inexpensive and can be administered in tablet or liquid form.

The medication is best taken on an empty stomach to ensure optimal absorption. It is also helpful to split the dose into two, with one being given in the morning and the other at night. It is important to give accurate doses; too much levothyroxine can cause symptoms associated with hyperthyroidism or cause a thyroxine overdose.


This condition occurs when the thyroid levels are too high or when too much levothyroxine has been consumed. Treatment options include radioactive iodine (facilities may be limited), chemotherapy, radiotherapy or anti-thyroid medication. Regular testing should be done after treatment to monitor the thyroid levels and/or any tumors or abnormal tissues.



Tumor removal depends on a variety of factors. The size of the tumor, its proximity to the esophagus and major arteries, and if it’s benign or malignant will help your vet determine the best course of action. Common treatments include biopsy, surgical removal, medication, chemotherapy or radiation.

Another possibility when treating either condition is the potential reversal to the other type. If a dog with low levels of thyroid hormones is given too much medication, symptoms of hyperthyroidism may appear. Alternatively, the same is true for a dog with hyperthyroidism given too much anti-thyroid medication or as a result of any procedures done to reduce thyroid hormone production.

Administer medications as accurately as possible. Do not miss vet appointments — regular monitoring of a thyroid condition will give your dog the best chance for managing the disorder and minimizing complications.

No two dogs are exactly the same. So what works for your neighbor’s dog may not work for yours. It is imperative to give your pet only the medication prescribed by your vet. Even if your dog seems to be feeling better or symptoms lessen, do not discontinue any medications without your vet’s approval.

Although a thyroid diagnosis can be disheartening, many times it can be treated. Pay attention to the symptoms, keep your vet appointments and follow all medication instructions to give your dog the best chance of living a long, healthy life.


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