Hypothyroidism in Cats (Feline Hypothyroidism): Symptoms, Treatment, and Life Expectancy
Key takeaways:
Cats with hypothyroidism have an underactive thyroid and may experience weight gain, lethargy, and other serious symptoms.
Hypothyroidism in cats is rare. It most often happens during or after cats are treated for an overactive thyroid.
There are several treatments for hypothyroidism. The condition can often be well controlled.
Table of contents
The thyroid gland plays an important role in a cat’s health. But when that gland doesn’t function correctly, it can cause serious problems, including hypothyroidism.
Hypothyroidism is when a cat’s thyroid is underactive. It’s somewhat rare in cats. However, it’s often closely linked to a much more common condition called hyperthyroidism (an overactive thyroid).
If you notice unusual symptoms, like poor coat quality and weight gain, then it’s important to take your cat to the vet. Hypothyroidism is treatable, and most cats recover.
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What is hypothyroidism (underactive thyroid) in cats?
Your cat’s thyroid produces hormones important for their health. Those hormones help control essential functions, including metabolism.
A cat who develops hypothyroidism has an underactive thyroid gland. It isn’t producing enough of the hormones their body needs to regulate their health.
Hypothyroidism is rare in cats.
What’s the difference between hypothyroidism and hyperthyroidism in cats?
Hypothyroidism is when a cat’s thyroid doesn’t make enough thyroid hormone to support the body’s functions. Hyperthyroidism occurs when the thyroid makes too much thyroid hormone. Hyperthyroidism is more common in cats than hypothyroidism.
What causes feline hypothyroidism?
Sara Ochoa, DVM, a veterinarian at Animal Hospital of West Monroe, explains that a cat can develop hypothyroidism for a couple reasons.
Hyperthyroidism treatment complication
Cats who have hyperthyroidism are often treated with methimazole. This medication lowers their thyroid levels. If the levels decrease too much, the cat can develop hypothyroidism.
Hyperthyroidism: Hyperthyroidism — when the thyroid gland makes too much hormone — is much more common in cats than hypothyroidism. Learn what to expect with hyperthyroidism in cats.
Not hungry? There are many reasons why your cat may suddenly lose their appetite. Check out some of the most common causes and when to seek help.
Annual checkups: Most cats should visit their veterinarian for a checkup at least once a year. Here’s why it’s important for their health.
Postsurgery hypothyroidism
It’s also possible for cats to develop hypothyroidism after they have surgery to remove part or all of their thyroid gland. Cats can also develop it after radioactive iodine treatment. These treatments are sometimes used to treat hyperthyroidism. But if they reduce thyroid levels too much, they can cause hypothyroidism.
Naturally occurring hypothyroidism
Cats can develop hypothyroidism naturally. While extremely rare, the condition can be caused by a disorder in the thyroid gland.
Congenital primary hypothyroidism
Another type of feline hypothyroidism is congenital primary hypothyroidism. This happens when kittens are born with an abnormal thyroid or a thyroid hormone deficiency. It’s usually discovered by the time a cat is a year old.
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Signs and symptoms of hypothyroidism in cats
The symptoms of hypothyroidism depend on how advanced the condition is. Cats who have a mild case of hypothyroidism may have minimal or no symptoms. You’ll generally notice symptoms of an underactive thyroid when the condition has progressed.
Symptoms of hypothyroidism in cats can include:
Weakness
Constipation
Weight gain
Lethargy or a lack of energy
Sensitivity to cold
Low body temperature
Matted hair
Hair loss
Unkempt appearance
Some cats may also have neurological changes due to hypothyroidism. Cats who are born with the condition may have severe tiredness, lack of appetite, decreased heart rate, and constipation. They may also be born with dwarfism.
How do vets diagnose hypothyroidism in cats?
Ochoa explains that vets use a blood test to diagnose hypothyroidism. “Your vet can easily draw blood and see if your cat has a low thyroid level,” she says. Vets commonly run a T4 or Free T4 blood test to confirm that a cat has hypothyroidism.
Treatment for hypothyroidism in cats
Most cats who are diagnosed with hypothyroidism won’t need to be treated. According to Ochoa, the right treatment for your cat will also depend on the cause of their hypothyroidism.
Hypothyroidism medication
Cats with more severe symptoms will need synthetic hormone supplements — usually an oral medication called levothyroxine. They should also receive follow-up blood tests to monitor their hormone levels.
Lower dose of methimazole
If your cat’s hyperthyroid treatment caused their hypothyroidism, your veterinarian may recommend changing their treatment plan. Reducing the dosage of methimazole will increase your cat’s thyroid levels. This should help treat the hypothyroidism.
Treatment with levothyroxine
“If your cat has developed hypothyroidism from a thyroidectomy or I-131 (radioactive iodine) treatment, your vet will prescribe your cat levothyroxine to help increase your cat’s thyroid levels,” Ochoa explains. This treatment may be lifelong depending on how severe your cat’s hypothyroidism is.
How long can cats live with hypothyroidism?
A cat’s prognosis and lifespan will depend on the cause of the hypothyroidism, said Ochoa. However, most cats recover well.
“Cats with hypothyroidism can be easier to treat and manage than cats with hyperthyroidism,” she says. “Rarely do we see cats with hypothyroidism die abruptly because of this condition.”
The bottom line
Hypothyroidism sounds like a scary diagnosis, but there are multiple treatment options. If you notice unexplained weight gain, lethargy, or poor coat quality in your cat, make an appointment with your vet. With treatment and monitoring, your cat should feel better and will likely recover.
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References
American Animal Hospital Association. (2023). Feline hypothyroidism.
Carolina Veterinary Specialists Charlotte. (n.d.). Hypothyroidism in cats — Causes, signs, & treatments.
Cornell University College of Veterinary Medicine. (n.d.). Feline thyroid tests.
Garcia, J. L. (2015). Hypothyroidism in cats — How is it diagnosed and treated? DVM360.
Heseltine, J. (2024). Hypothyroidism in animals. Merck Veterinary Manual.
Peterson, M. E., et al. (2018). Disorders of the thyroid gland in cats. Merck Veterinary Manual.
Veterinary Specialty Center Tuscon. (n.d.). Hypothyroidism in cats - Signs of an underactive thyroid.
