Thyroid Problems

Information to help cats and dogs with symptoms of canine and feline thyroid problems.

Select a Topic

  1. What are Thyroid Problems?
  2. What Causes Thyroid Problems?
  3. Diagnosing Thyroid Problems
  4. Help for Thyroid Problems

What are Thyroid Problems in Pets?

The thyroid is a small, butterfly-shaped gland in neck, in front of the trachea (windpipe). This gland, which is part of the endocrine system, produces two hormones: thyroxine (T4) and triiodothyronine (T3). These two hormones regulate and maintain your pet’s metabolism, which affects overall health and well-being.

The production of these hormones is controlled by another hormone called TSH (thyroid stimulating hormone). TSH is produced by the pituitary gland.

If the thyroid gland doesn’t function properly, thyroid hormone levels can be too high or too low. These hormones affect nearly every organ in the body. As a result, thyroid disease can cause other related problems. Improper thyroid function can negatively affect your pet’s body weight, heart rate, skin and coat, digestive system and reproductive health.

What Causes Pet Thyroid Problems?

There are two types of thyroid disease – hypothyroidism and hyperthyroidism.

Hypothyroidism is mainly a problem in dogs, rarely occurring in cats. When hypothyroidism occurs, the thyroid gland is underactive. This means not enough hormone is produced, which slows down the pet’s metabolism.

The exact cause is unknown, but hypothyroidism in dogs may be caused by an auto-immune response in which the dog’s own immune system kills thyroid gland cells. Dogs that suffer from recurring skin problems often have hypothyroidism.

Clinical signs of hypothyroidism in dogs include:

  • Weight gain or obesity
  • Lethargy and lack of energy
  • Dry skin and hair loss
  • Constipation
  • Slow heart rate
  • Anemia
  • Intolerance to cold
  • High blood cholesterol
  • Infertility
  • Seizures

Behavioral changes may also occur and include anxiety, depression, and hyperactivity, as well as being unfocused or passive.

Hyperthyroidism (also called thyrotoxicosis)
Hyperthyroidism typically affects middle-aged and older cats (between 4 and 22 years of age), seldom developing in dogs. When feline hyperthyroidism occurs, the thyroid gland is overactive and produces too much hormone, speeding up the metabolism of affected cats. The cause of hyperthyroidism has been established, but dietary, immunological, genetic and environmental factors may also contribute to hyperthyroid cats.

Clinical signs of hyperthyroidism in cats include:

  • Weight loss
  • Increased appetite
  • Diarrhea
  • Vomiting
  • Intolerance to heat
  • Dull, dry or oily coat with excessive shedding
  • Rapid/fast breathing
  • Increased water consumption accompanied by urination
  • Increased or decreased activity
  • Tremors

Behavioral changes such as nervousness, restlessness, hypersensitivity or stress may also occur.

Diagnosing Thyroid Problems in Pets

Diagnosis is based on symptoms. Your vet will conduct a thorough physical examination and review your pet’s medical history to diagnose hypothyroidism or hyperthyroidism. If a problem is suspected, the vet will do appropriate diagnostic tests such as a Baseline T4 Test, Baseline T3 Test or TSH Stimulation Test.

Generally, the TSH Stimulation Test will reveal whether your dog has a low T4 or T3 level. If hyperthyroidism is suspected, the diagnosis is based on the symptoms presented, enlarged gland, and high T4 levels.

If symptoms of other diseases are present along with hyperthyroidism, your vet may perform blood tests such as a CBC (complete blood count), serum chemistry and urinalysis. Tests such as the T3 suppression test, free T4 measurement test, and a thyrotropin-releasing hormone stimulation test may be performed to confirm the diagnosis of hyperthyroidism.

How to Treat Pet Thyroid Problems

Treatment of hyperthyroidism in cats

Your vet may recommend the standard hyperthyroidism treatment:

  • Radioactive iodine therapy (I-131) – The top choice in treatment by many vets. Radioactive iodine is injected and absorbed into the bloodstream. The thyroid gland takes up the iodine, which is required to make T3 and T4. The radiation kills the abnormal thyroid tissue but doesn’t destroy the surrounding area. Most cats treated with radioactive iodine return to normal hormone levels within 2 weeks of treatment.
  • Anti-thyroid medication such as methimazole (tapazole) – Medication doesn’t cure the disease but does help control it. Dosage is usually twice a day by mouth, for life. The medication is relatively inexpensive. Side effects can include vomiting, fever, lethargy and anemia. Transdermal (through the skin) antithyroid medications are also available. With either form of medication, the cat will need regular blood tests to check for side effects and measure effectiveness.
  • Surgical removal (thyroidectomy) – Surgical removal has a high success rate. Surgery usually results in a permanent cure.

These treatments have possible adverse side effects, such as liver damage, anemia, hair loss and lethargy. Cats undergoing radioactive iodine therapy should be kept away from pregnant women and children.

Treatment of hyperthyroidism in dogs

Treatment of hyperthyroidism involves a daily dose of synthetic T4 hormone known as thyroxine (levothyroxine). Follow-up blood tests will be taken in about six weeks to check for improvement. This is life-long therapy, but dogs typically tolerate it well and go on to enjoy good health for the rest of their lives.


There are several things you can do to help prevent hypothyroidism or hyperthyroidism in pets:

  • Diet - Feed your cat or dog a natural, well-balanced diet that contains all the essential vitamins, minerals and nutrients
  • Exercise – Ensure your pet gets enough regular exercise
  • Check-ups – Take your pet to the vet for annual check-ups and monitor any physical or behavioral changes
  • Education – If your pet is diagnosed with hypothyroidism or hyperthyroidism, become as knowledgeable as possible about the problem.
  • Supplements – Try natural remedies, such as Thyro-Pet™ for Cat & Dog Thyroid Health and Thyroid Soothe™ for Pet Hyperthyroidism Symptoms
  1. Colman, Stephanie. “Treating Your Dog’s Hypothyroidism.” Whole Dog Journal. Accessed October 5, 2019.
  2. “Hypothyroidism in Dogs—There’s an FDA Approved Drug to Treat It.” U.S. Food & Drug Administration. Accessed October 5, 2019.
  3. Leonardi, Lauren. “Thyroid Problems in Dogs: A Guide to Hypothyroidism.” PetCareRx. Accessed October 5, 2019.
  4. “Hyperthyroidism in Cats.” Cornell University College of Veterinary Medicine. Accessed October 5, 2019.
  5. Desfosse, Rebecca. “5 Signs You Should Get Your Cat’s Thyroid or Dog’s Thyroid Checked.” PetMD. Accessed October 5, 2019.
  6. “Hypothyroidism in Dogs.” Washington State University. Accessed October 5, 2019.
  7. “Disorders of the Thyroid Gland in Dogs.” Merck Manual Veterinary Manual. Accessed October 5, 2019.
  8. Burke, Anna. “Thyroid Disease in Dogs.” American Kennel Club. Accessed October 5, 2019.
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