Hyperthyroidism vs Hypothyroidism: Cats vs Dogs

Hyperthyroidism vs Hypothyroidism: Cats vs Dogs

Just like people, cats and dogs also have thyroid glands located in their necks that secrete hormones that regulate their metabolisms; if the hormone is low, then the metabolism will be low, if the hormone is high, the metabolism is also high.

When it comes to thyroid disease in dogs and cats, cats generally have HYPERthyroidism, an overactive thyroid (and acceleration of your cat’s metabolism), whereas dogs tend to have HYPOthyroidism, an underwhelming production of the necessary thyroid hormones (and corresponding slowing of your dog’s metabolism).

Signs and Symptoms:


  • Lots of energy
  • Weight loss
  • Increased appetite
  • Increased thirst and urination
  • Increased vocalization
  • Vomiting
  • Diarrhea
  • Hair loss
  • Excessive scratching
  • Increased heart rate
  • High blood pressure

Hyperthyroidism tends to be more common in older cats and is very rare in dogs, and when found in dogs, is generally associated with some form of cancer.

Picture credit: Advanced Veterinary Medical Imaging


  • Hair loss
  • Itchy and flaky skin
  • Weight gain
  • Ear infections,
  • Muscle loss
  • Depression or sluggishness
  • Behavioral changes including aggression or anxiety
  • Intolerance to cold temperatures
  • Slow heart rate
  • High cholesterol
  • Head tilting

Hypothyroidism tends to occur more frequently in medium to large breed dogs that are generally middle-aged.

Picture credit: Getty Images


For both cats dogs, diagnosis is based on clinical signs in conjunction with testing”usually blood tests to identify your pet’s T4 concentration. In cats, there is often an enlargement of the thyroid gland which can be discovered with palpation of the neck. Other conditions such as underlying adrenal issues can cause thyroid abnormalities so careful testing can be important.


If you see some of the symptoms listed above, talk with your veterinarian. These diseases can be fairly easy and inexpensive to treat and can save your cat’s life as well as vastly improving the quality of life of your dog.

If all tests and signs point to your pet having thyroid issues, don’t fret, there are treatments available. The most common treatment for dogs is a man made hormone called L-thyroxine, given orally. For cats, radioactive iodine (I-131) treatment is often curative but is costly. Surgery to remove the benign tumor causing the enlargement is an option but is less often recommended. Medication (Methimazole) given orally or transdermally or dietary therapy focused on a reduction of iodine content are also often effective options. Each treatment option has its advantages and disadvantages and choice will depend on overall health status, human caregiver’s willingness to administer medications regularly, and financial considerations.

Left untreated, hyperthyroidism can result in life-threatening weight loss or secondary complications such as heart disease in your cat. Hypothyroidism, though rarely fatal, will affect your dog’s quality of life. However, with proper diagnosis and medications, therapies or surgery, your pet can still live a long and happy life.

More Information

What You Need to Know About Thyroid Disease in Dogs and Cats

Hyperthyroidism in Cats

Your Dog Has Hypothyroidism or Does She?