Symptoms of Hypothyroidism in Cats

Symptoms of Hypothyroidism in Cats
Joseph Menicucci
Joseph Menicucci

Hypothyroidism in cats is inadequate functioning of the thyroid gland. It appears when the thyroid levels are too low, and body systems can be compromised.

When a cat is hypothyroid, they typically have some weight gain, a lack of desire to play, or a matted and unkempt appearance. Cats who have hypothyroidism may be intolerant to cold and low body temperature. There may also be some behavioral issues present.

It is more common for cats to experience hyperthyroidism rather than hypothyroidism. If you want to find out further about the symptoms of hypothyroidism in cats, take a peek at this article.

What is the Thyroid Gland in Cats?

The thyroid is a butterfly-shaped gland positioned just below the larynx, near the front of the neck. The thyroid secretory organ is made up of two lobes. They are on each side of the windpipe, affixed deep into the soft tissues of the larynx. The thyroid gland creates hormones that control thyroid function. The thyroid regulates many essential functions or systems in the body:

  • Heart function
  • Muscle function
  • Digestive function
  • Body temperature
  • Brain development
  • Bone maintenance
  • Respiratory weight
  • Bodyweight

The thyroid gland helps to regulate many different organ functions. Even though hyperthyroidism is more prevalent in cats, hypothyroidism is also detrimental to your cat’s health.


What is Hypothyroidism in Cats?

Hypothyroidism is when the thyroid gland slows down and is underactive because it does not generate enough thyroid hormones. When the thyroid slows down, so does the metabolism. The thyroid stores and delivers thyroid hormones in the body. These hormones are universally known as T3 and T4. The thyroid needs iodine to create these hormones.

The hormone calcitonin is another essential thyroid hormone. It is responsible for regulating calcium levels in the body. The parathyroid glands increase calcium levels in the blood. It also helps to maintain the levels of phosphorus in the body.

The hormone generated by the thyroid gland is controlled by the quantity of thyroid-stimulating hormone created by the pituitary gland. The hypothalamus, situated directly above the pituitary gland, delivers messages to the brain and controls the TSH.

If your cat is hypothyroid, it means that they are not producing enough T3 or T4 hormones to sustain the health of their thyroid. However, if your cat is hyperthyroid, it means that they are producing too many T3 and T4 hormones.

What Are the Symptoms of Hypothyroidism in Cats?

If your cat is hypothyroid, there are symptoms that they may develop, especially if it is severe. The symptoms of hypothyroidism depend on how far along the condition is. There are some common signs of hypothyroidism you need to watch out for:

  • Weight gain despite no increase in food intake
  • Lack of appetite
  • Poor coat condition
  • Weakness
  • Low energy Constipation
  • Neurological changes
  • Mental dullness
  • Low body temperature
  • Low heart rate
  • Excessive thirst
  • Sensitivity to cold

Cats with low thyroid hormone levels may also lose some of their hair. Some cats with hypothyroidism may also begin to go potty outside of their litter box. Many pet parents do not know that if their cat does this, it can be triggered by a medical condition. 

Some vets think there is also a connection between behavior issues and low thyroid hormone levels in cats. Some cats who have hypothyroidism may develop aggressive or compulsive behavior. Your vet can diagnose hypothyroidism with a simple blood test.


What Causes Hypothyroidism in Cats?

There are two primary reasons why cats can develop hypothyroidism. Cats can become hypothyroid if they are given excessive thyroid hormone replacement. Cats with hyperthyroidism are often treated with specific medication that lowers their thyroid levels. If a cat’s thyroid levels decrease too much due to the medicine, they may become hypothyroid.

Cats may also become hypothyroid if they have surgery to remove part or all of their thyroid gland. It can occur after they have radioactive iodine treatment. This treatment can sometimes be employed to treat hyperthyroidism. If the therapy decreases thyroid levels too much, it can cause hypothyroidism.  

In rare cases, cats can also be born with hypothyroidism. These cats may demonstrate sure signs of hypothyroidism, including dwarfing. Congenital hypothyroidism is a hormonal cause of dwarfism in cats. Suppose a cat has a congenital condition that they have had since birth. Cats born with congenital hypothyroidism are typically normal in size for the first few weeks.

However, as time passes, their fur does not grow properly, and they may have short legs and a large head. They may also suffer from mental dullness and lack of energy. Fortunately, these sweet fur babies can be treated with lifelong administration of synthetic thyroid hormone and maintained with the help of an attentive, caring vet and regular bloodwork.

What is the Treatment for Hypothyroidism in Cats?

The vet can treat your cat with hypothyroidism with synthetic thyroid hormone. The medication is prescribed according to your cat’s weight. The dosage may need to be periodically adjusted, so you must maintain a good relationship with your vet. Once your cat’s medicine is at the right level, you will need to bring your fur baby back for a follow-up every six months.

With treatment, your cat will live everyday life, as they will become spryer and more active. They will become more like their old self. Their hair typically begins to grow back within the first week of treatment. However, more time is required for your cat to grow all their hair back. Most cats will start to lose weight within the first couple of weeks on the medicine.

Within the first few weeks of medication, the symptoms should calm down and become more manageable. Your cat will be a much happier and healthier feline.


Why is Hypothyroidism in Cats Considered Rare?

Studies have indicated that spontaneous adult-onset primary hypothyroidism does exist. However, research tends to focus on the hyperthyroid condition. Often, cats will only demonstrate mild clinical symptoms of hypothyroid, which is compounded by a lack of awareness of the disease by clinicians who think it is far too rare to be considered.

Better research can only be conducted if clinicians accept that the condition is more prevalent than initially believed. Hypothyroidism in cats does not depend on the type of breed. In the study showed, it was determined that males were more susceptible. With that said, hypothyroidism in cats is still a rarity.

The study shows that there are other reasons that cats develop hypothyroidism than those previously having hyperthyroidism, and treatment overcorrects the problem. The condition is acquired hypothyroidism, with primary hypothyroidism being an immune-mediated disorder that attacks thyroid tissue.

Adult cats with acquired hypothyroidism typically have a good prognosis if treatment is given. These cats can achieve an excellent long lifespan. Weight management may be the key to success.



If your fur baby is hypothyroid, it is your responsibility as a pet parent to ensure they get the best treatment possible. Hypothyroidism in cats may be rare, but it is a severe condition that should not be overlooked.



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