Unfortunately, feline hyperthyroidism is a fairly common endocrine disease in cats. It is a disorder which is characterized by the overproduction of thyroid hormone and an increase in the cat’s metabolic rate.

Hyperthyroidism occurs when one or both of the thyroid glands become overactive and subsequently enlarged. Even though the thyroid gland does become enlarged, it is usually benign, and malignancy actually occurs in less than 2% of all hyperthyroid cases.

This disorder affects many of the cat’s internal organs, especially the heart, causing it to pump faster and more vigorously. Eventually, the heart starts increasing in size in an attempt to meet the body’s increased demand for blood flow. However, all the extra pumping pressure leads to a greater output of blood and high blood pressure ensues. In fact, approximately 25% of cats who have hyperthyroidism also experience high blood pressure.

Symptoms of Feline Hyperthyroidism

Hyperthyroidism affects mostly middle aged or senior cats. Since a cat’s thyroid glands are responsible for controlling the cat’s metabolic rate, a cat with feline hyperthyroidism will have an increased appetite as well as seem to be continually thirsty. However, they may still lose weight rapidly even though they will seem to be ravenous and eat anything that they find. Some cats with hyperthyroidism lose weight so slowly that their owners do not even realize it until their vet or someone else points it out. In a few cases, the cats develop anorexia as the disease gets progressively worse.

Other symptoms include:

Frequent urination




Dull coat

Congestive heart failure


Increased heart rate


High blood pressure is also associated with feline hyperthyroidism. It should also be noted, however, that the elevated blood pressure in a few cats can lead to retinal hemorrhage or detachment which can result in blindness.

Congestive heart failure, arrhythmias, and an increased heart rate are also common cats with hyperthyroidism.

Causes of Feline Hyperthyroidism

The occurrence of adenomas in the thyroid gland of cats is one of the most common causes of feline hyperthyroidism. Adenomas are clusters of non-cancerous cells which materialize inside the cat’s gland. Although quite rare, feline hyperthyroidism can also be caused by the growth of cancerous cells.

Researchers have determined that both environmental and dietary factors do play a part in a cat’s risk of developing hyperthyroidism, although they are not able to agree exactly how.

Whilst there is no individual cat breed that is at an increased risk of hyperthyroidism, there are more known cases of Siamese cats developing hyperthyroidism than any other breed.


In order to properly diagnose hyperthyroidism, a veterinarian will usually perform a blood test that is designed to determine the blood level of one of the thyroid hormones, called thyroxine (or T4). Most often the T4 level is so high that the veterinarian can easily diagnose hyperthyroidism, but in some cases a cat’s T4 levels may appear in the upper range of normal cats. If this happens, then the veterinarian will have to perform another test called a T3 Suppression Test. Another alternative is for the cat’s thyroid to be scanned at a specialty veterinary hospital.

Some cats with hyperthyroidism have protruding thyroid glands that the veterinarian can easily feel through the cat’s skin.


Sadly, since most cats with hyperthyroidism are already in their old age, some cat owners mistakenly believe that offering their cat any treatment would be futile.

Cat owners need to keep in mind, however, that seniority in cats does not equal a disease.


Your veterinarian will recommend a course of treatment that might include surgery, medication, and radioactive iodine.

Medication in the form of anti-thyroid drugs are often prescribed as the first course of treatment and will most probably be required by your cat for the remainder of its life.

Surgery is often performed to remove one or both of the thyroid glands.

Using radioactive iodine is usually the last course of action that a veterinarian will undertake, as the iodine kills all thyroid tissue in a cat’s body.

Alternative Treatment

Whilst traditional treatments may be too expensive for some cat owners, there are other options, like Thyroid Support Gold. Made up of 7 different herbal extracts, Thyroid Support Gold is an all-natural remedy created by a leading naturopathic veterinarian to be an effective treatment that inhibits over-production of thyroid hormones, whilst also improving a cat’s cardiovascular functions. Another great benefit of Thyroid Support Gold is that not only does it help improve a cat’s digestion but it also is safe for long-term use.

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