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    What Changes in Behavior Will I See If My Cat Has Hyperthyroidism?

    Topic: Thyroid

    The main changes that you might notice in your cat’s behavior if she develops hyperthyroidism are as follows:

    Increased thirst

    Cats with hyperthyroidism often begin drinking more water than before. You may notice that they stand at the water bowl more often, jump on counters and beg for the faucet to be turned on, or stick their paws in the water glass that you left on the end table. Subsequently, hyperthyroid cats urinate more, and this may result in inappropriate urination, or urinating outside of the litter box.


    Cats with increased thyroid hormone levels may begin to act hyper, restless, or nervous. Your cat might be more skittish about noises or new people, or you may just notice an overall increase in activity level.


    Hyperthyroid cats have a tendency to behave anxiously. They may seem confused and pace a lot. Howling and crying at night is very commonly seen in these cats as their increased metabolic rates have them feeling nervous and looking for company while you try to sleep.


    You may notice panting or an increased breathing rate in your hyperthyroid cat. This may also be a sign of a respiratory or heart condition and should be checked out by your veterinarian immediately.

    Developing a demanding nature

    Your previously mild-mannered cat may become more demanding if she develops hyperthyroidism. She may vocally and pushily plead unrelentingly for food, water, or attention. Though she may not have ever been a cat that required constant interaction with you before, she may now suddenly be underfoot at all times.

    Vomiting and diarrhea

    Hyperthyroidism can disrupt your cat’s gastrointestinal motility and result in increased vomiting and diarrhea. You may also notice an increased frequency or volume of otherwise normal stool.

    Increased appetite

    If your cat develops hyperthyroidism, you are very likely to find yourself filling her food bowl more often. People often notice this sign of hyperthyroidism before any of the others develop.

    Increased desire to eat non-cat food items

    Hyperthyroid cats often start trying to get up on counters or tables to steal human food, when they’ve never done so before. They may even try and swipe it right out of a person’s hand. This behavior may extend to eating items that aren’t food at all, even if a cat has never eaten foreign objects before. Some common items for hyperthyroid cats to eat are fabric, paper, and string.

    Weight loss

    While not a behavioral change, weight loss in an older cat is a hallmark of hyperthyroidism and is something that you will notice at home. This weight loss occurs in spite of the increase in appetite discussed above.

    Poor hair coat

    Another sign of hyperthyroidism in cats that is not behavioral but is readily noticed by owners is the development of a coarse, dull hair coat.

    A Note on Apathetic Hyperthyroidism

    Sometimes a cat with hyperthyroidism shows completely opposite behaviors from those listed above. This cat may act depressed, sluggish, stop eating as much, and generally act slow. These cats still lose weight, but their behavioral signs don’t fit into the classic hyperthyroid mold. This is apathetic hyperthyroidism, and it affects less than 5% of hyperthyroid cats.

    What About Physical Signs of Feline Hyperthyroidism?

    Signs of hyperthyroidism that you are not likely to notice at home but which may be found on a physical exam when you take your cat to the veterinarian include:

    • Increased heart rate This is part of the general increase in metabolism that is caused by hyperthyroidism.
    • Increased blood pressure is commonly noted in hyperthyroid cats. It will generally resolve once the thyroid condition is treated. Without treatment, high blood pressure can result in kidney damage and blindness.
    • Heart murmur may be present when your veterinarian listens to your cat’s heart with a stethoscope. Cats with hyperthyroidism can go on to develop heart failure if the thyroid condition is left untreated.
    • Changes in blood-work results including increased ALT (a liver function enzyme) and total and free T4 levels are usually seen in hyperthyroid cats.

    Knowing the behavioral changes to watch for can help you get your cat’s thyroid condition diagnosed and treated sooner.

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    Meet Our Expert

    Dr. Janice Huntingford

    Pet Wellbeing's own Dr. Jan has been in veterinary practice for over 30 years. Since receiving her Doctor of Veterinary Medicine at the Ontario Veterinary College, University of Guelph, she's founded two veterinary clinics and lectured extensively on pet herbal therapy, nutraceuticals, acupuncture, rehabilitation and pain management.

    Dr. Jan has studied extensively in both conventional and holistic modalities, helping us to formulate all of our supplements. She is an essential part of Pet Wellbeing.

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