You want your cat to feel happy and healthy long into their golden years. We want that for your cat, too. That’s why we wanted to cover an important disorder that cat owners need to be aware of—hyperthyroidism in cats.

Hyperthyroidism is an endocrine disorder that affects a significant portion of the feline population. Cats are increasingly at risk as they age.

But what is hyperthyroidism in cats? What are the symptoms? Most importantly, if your cat has hyperthyroidism, how can you treat the disorder? We’ve answered that and more to ensure your cat goes on to live a long, healthy life.

What is hyperthyroidism in cats?


Before we dive into how to spot hyperthyroidism in your cat (and, more importantly, how to treat it), let’s quickly cover what hyperthyroidism is.

“Feline Hyperthyroidism is one of the most common endocrine diseases in cats, and affects over 10 percent of cats 10 years or older in the United States,” says Turnera Croom, DVM, a veterinarian with a mobile veterinary practice in Southwest Michigan.

When it comes to what causes hyperthyroidism in cats, there are no definitive answers. “Unfortunately, we do not completely understand the origin of hyperthyroidism in cats; it is most likely that there are multiple influencing factors,” says Robin Downing, DVM, veterinarian and hospital director of The Downing Center for Animal Pain Management in Windsor, CO. “That said, there has been a linkage described between certain fire retardants used in carpet and upholstery and an increased risk of hyperthyroidism. Another theory is that BPA, which is often used to line metal food cans, may serve as an endocrine disruptor and have a toxic effect on the thyroid gland.”

Diet may also play a role. “We know that many, if not most, cat foods (especially those with fish as the primary protein source) have very high levels of iodine,” says Dr. Downing. “Increased intake of iodine over a lifetime may contribute to the development of hyperthyroidism in certain [cats].”

What are the symptoms of hyperthyroidism in cats?


Initially, hyperthyroidism in cats can be hard to spot. Symptoms may be mild at the beginning of the disorder, and certain symptoms can mimic other issues. For example, vomiting can be a sign of hyperthyroidism in cats—but it can also be a sign of indigestion or cat hairballs. That’s why it’s so important to know exactly what to look out for. If you have hyperthyroidism symptoms on your radar, you can keep an eye on your cat—and get them the proper veterinary attention as soon as they start exhibiting potential signs of hyperthyroidism.

According to PetMD, symptoms of hyperthyroidism in cats include:

  • Hyperactivity
  • Increased appetite
  • Weight loss—despite increased food intake (“A cat with hyperthyroid will eat voraciously, but will still lose weight over time,” Dr. Croom explains.)
  • Vomiting
  • Diarrhea
  • Increased thirst and water intake
  • Increased urination
  • Restlessness (“A common client complaint is that these cats [with hyperthyroidism] are restless at night, wandering the house and vocalizing,” Dr. Downing adds.)
  • An unkempt or greasy coat

Hyperthyroidism can cause serious health issues for your cat. “If left untreated, a kitty with hyperthyroidism will continuously lose weight from the circulating thyroid hormones,” says Dr. Croom. “[They] will routinely have increased body temperature, heart and respiration rates, and hyperactivity, which could lead to hypertension.”

And hypertension brings its own set of challenges. “Hypertension can be so severe that they actually detach their retinas and become blind,” says Dr. Downing. “Hypertension can [also], in turn, lead to kidney disease and pathologic changes in the heart muscle.”

Bottom line: if you suspect your cat might be struggling with hyperthyroidism or they’re exhibiting even minor symptoms, it’s important to get them to the vet and on a proper treatment protocol ASAP.

How is hyperthyroidism in cats diagnosed?

Read more here