Warning Signs Your Cat is Dying of Thyroid Disease and How to Help

Has your aging cat been acting differently lately? Have they lost weight, seem restless, or drink and urinate more? These could be signs of a serious but treatable condition called hyperthyroidism.

In this comprehensive guide, you’ll learn:

  • What is feline hyperthyroidism and what causes it
  • The most common signs your cat’s thyroid is out of whack
  • How vets diagnose overactive thyroid in cats
  • Conventional treatment options for feline hyperthyroidism
  • Tips for managing side effects of thyroid medication
  • Natural remedies to ask your vet about
  • How to improve your hyperthyroid cat’s quality of life
  • When it’s time to let go and tips for saying goodbye

If caught early, thyroid disease treatment can add many healthy years to your cat’s life. Read on to educate yourself on supporting your feline friend through this challenging but manageable condition.

What is Hyperthyroidism in Cats?

The thyroid is a small gland located in the neck that controls your cat’s metabolism. It does this by producing two hormones, thyroxine (T4) and triiodothyronine (T3).

Hyperthyroidism occurs when the thyroid gland overproduces these hormones. This speeds up your cat’s metabolism, causing rapid and potentially dangerous weight loss.

Experts aren’t sure what causes feline hyperthyroidism. However, these factors are believed to play a role:

  • Age – Most commonly affects cats over 10 years old
  • Diet – Cats fed mostly canned food are more prone
  • Environmental toxins – Exposure to fire retardants, fertilizers, etc
  • Cancer – Benign nodules on the thyroid can form
  • Genetics – Purebred cats like Siamese may be predisposed

For unknown reasons, hyperthyroidism in cats is on the rise. Vets diagnose feline hyperthyroidism in around 2% of cats over 10 years old. By age 15, as many as 10% of cats may suffer from an overactive thyroid.

Left untreated, hyperthyroidism can lead to dangerous health complications for cats:

  • Heart problems – like murmurs, arrhythmias, and heart failure
  • Hypertension – high blood pressure can damage kidneys
  • Loss of lean muscle mass – despite increased appetite
  • Kidney disease – exacerbated by high metabolism
  • Collapsing trachea – weakened windpipe causes coughing/gagging
  • Vomiting and diarrhea – from inflammation in the digestive tract
  • Increased urination and liver enzymes – indicative of organ stress

Fortunately, with early detection and proper treatment, many hyperthyroid cats can regain their health and live happily for years.

12 Signs Your Cat’s Thyroid is Overactive

Gradual weight loss in cats is easy to overlook. But rapid slimming down can be one of the first red flags of an overactive thyroid gland.

Here are 12 common symptoms of hyperthyroidism in cats:

1. Sudden Weight Loss

Most cats with hyperthyroidism eat more yet continue losing weight. They burn calories faster than they can take them in.


  • Weigh your cat monthly to catch weight trends early
  • Track how much food they eat each day
  • Calculate average weight loss per week or month
  • Report any rapid weight drop to your vet asap

2. Increased Appetite

Excess thyroid hormones accelerate metabolism, making cats feel constantly hungry.

You may notice your cat:

  • Begging for food constantly
  • Finishing meals very quickly
  • Stealing others pets’ or human’s food
  • Chewing on non-edibles like plastic, paper, or houseplants

Tip: Split meals into 3-4 smaller portions spaced throughout the day to help satisfy your ravenous kitty.

3. Gastrointestinal Upset

Vomiting, diarrhea, and other stomach issues are common. This can be from:

  • Eating too quickly
  • Inflammation from high thyroid hormone levels
  • Poor nutrient absorption


  • Feed a bland diet of boiled chicken and rice to settle the stomach
  • Give anti-nausea medication if vomiting is frequent
  • Have your vet test for food allergies or intolerances

4. Poor Fur Coat

Thyroid problems lead to poor nutrition and stress that affects your cat’s coat.

You may notice:

  • Dull, dry fur lacking shine and softness
  • Increased shedding and bald patches
  • Slow fur regrowth after grooming
  • Seborrhea or dandruff

Tip: Brush frequently with a Furminator to remove loose hair and distribute oils. Ask your groomer about conditioning treatments.

5. Increased Thirst and Urination

Excess drinking and peeing is common as the body tries to flush out excess thyroid hormones.

Signs include:

  • Urinating outside the litter box
  • Waking you up at night to drink water
  • Leaving behind larger than normal wet spots
  • Showing new interest in sinks, showers or toilets


  • Use low-sided ceramic water bowls
  • Give wet food with high moisture content
  • Use cat fountains to encourage drinking
  • Keep multiple fresh water sources around home

6. Hyperactivity

You may notice a sudden increase in your cat’s energy and restlessness.

Watch for:

  • Constantly jumping on and off furniture
  • Pacing, inability to get comfortable
  • Excessive time spent at windows observing outdoors
  • Begging to go outside more than usual

Tip: Increase interactive playtime to help your restless kitty burn off energy.

7. Irritability or Anxiety

Thyroid dysfunction can cause personality changes in cats.

Your once-mellow kitty may seem:

  • More vocal than normal, especially at night
  • More clingy and demanding of attention
  • More easily startled by noises or activity
  • More aggressive towards humans or other pets


  • Try calming treats, sprays or diffusers with catnip or pheromones
  • Stick to consistent daily routines for feeding, play, and sleep
  • Give your cat safe hiding spots to retreat to when stressed

8. Fast Breathing or Panting

Rapid overproductive thyroid function speeds up respiratory rate. You may notice:

  • Panting with tongue hanging out
  • Breathing with an open mouth
  • Noticed movements of the abdomen with each breath

Tip: Time how many breaths per minute your cat takes when at rest. Report rapid breathing over 40 breaths per minute to your vet.

9. Fast Heart Rate

Palpitations or a racing pulse are common as the heart works harder to support a revved-up metabolism.


  • Feel your cat’s heartbeat by gently placing your hand against their chest when they are relaxed
  • Count the pulses for 15 seconds then multiply by 4 to get beats per minute
  • Tell your vet if your cat’s resting heart rate exceeds 220 to 240 beats per minute

10. High Blood Pressure

Hyperthyroidism often leads to high blood pressure, called hypertension. This requires medication to control and prevent organ damage.

Symptoms may include:

  • Blood in urine or stools
  • Dilated pupils
  • Retinal detachment or blindness
  • Blood clots
  • Temporary paralysis of limbs
  • Seizures or fainting

Tip: Ask your vet check your hyperthyroid cat’s blood pressure at each visit. Optimal BP is below 150/95 mm Hg.

11. Muscle Wasting

Despite hunger, cats burn muscle faster than they can build it. You may notice:

  • Loss of muscle over back, shoulders and hind limbs
  • Hind leg weakness causing a hopping gait
  • Difficulty jumping up to favorite spots
  • Reluctance to groom hard-to-reach areas


  • Encourage exercise like climbing stairs or perching on cat trees
  • Brush and massage your cat frequently
  • Talk to your vet about physical therapy or acupuncture

12. Enlarged Thyroid Gland

In some hyperthyroid cats, you can see or feel thyroid nodules in the neck as the gland enlarges and protrudes. Look for:

  • Firm lumps in front of the trachea toward the chin
  • A visibly thickened neck
  • Your cat resenting you touching their neck

Tip: Point out any lumps, bumps or swelling you find to your veterinarian.

If your aging cat is displaying several of these symptoms, don’t delay in making a vet appointment. The sooner hyperthyroidism is diagnosed, the better the outcome for your cat.

How Vets Diagnose Hyperthyroidism in Cats

There is no single definitive test for feline hyperthyroidism. Vets will combine:

Physical Exam

Checking for:

  • Enlarged thyroid gland
  • Fast heart rate and rapid breathing
  • High blood pressure
  • Heart murmurs or arrhythmia
  • Weight loss despite good appetite
  • Poor hair coat and muscle tone

Blood Tests

  • Thyroid hormone (T4) level – Elevated T4 confirms diagnosis. Normal is < 2.5 mcg/dL
  • Complete blood count – May show anemia, liver or kidney issues
  • Chemistry panel – Assesses organ function and blood sugar
  • Urinalysis – Checks for signs of kidney dysfunction

Additional Testing

Other tests that may be recommended:

  • Thyroid biopsy – To check for cancer if thyroid is enlarged
  • Radiographs (x-rays) – Views heart and chest for abnormalities
  • Heart ultrasound – Checks heart function if murmur is present
  • Blood pressure – High in many hyperthyroid cats

Conventional Medical Treatment for Feline Hyperthyroidism

The conventional treatment for hyperthyroidism involves reducing thyroid hormone production with:

1. Medication

Oral medication blocks excess hormone production. Options include:

  • Methimazole – Most common, taken twice daily
  • Carbimazole – Turns into methimazole in the body
  • Thyrozine – Blocks thyroid hormone absorption

Cats normally improve within 3 weeks on medication but it must be given for life. Side effects like vomiting or lethargy may need dose adjustments.

2. Radioactive Iodine Therapy

A single injection of radioactive iodine destroys overactive thyroid tissue. This is the closest thing to a cure. However, it requires at least a week of isolation at a specialty vet clinic.

3. Surgery

Removing part or all of the thyroid gland reverses hyperthyroidism. This requires general anesthesia and has more risks than other options.

4. Diet

Prescription foods containing limited iodine may help normalize thyroid function in mild cases. Work with your vet to avoid iodine deficiency.

In many cats, a combination of methimazole medication and radioactive iodine therapy provides the best results long-term.

Managing Side Effects of Hyperthyroid Medication

Oral methimazole or carbimazole drugs often cause side effects like:

  • Lethargy – from lowering metabolism too much
  • Poor appetite – adjust schedule and diet to encourage eating
  • Vomiting – give anti-nausea meds if needed
  • Facial itching – antihistamines provide relief
  • Low white blood cell count – monitor counts regularly

Tips to minimize side effects:

  • Give medication with food to reduce stomach irritation
  • Start with a low dose and increase gradually
  • Give as a transdermal gel if your cat won’t take pills
  • Split daily dose into twice daily to improve tolerance
  • Schedule doses when your cat normally eats
  • Follow up with your vet frequently for dose adjustments
  • Report any side effects promptly so medication can be adjusted

With close monitoring and patience, your cat can tolerate thyroid medication well and feel much better within a few weeks or months.

4 Natural Remedies to Discuss with Your Vet

Some cat owners wish to take a more natural approach to managing feline hyperthyroidism. Always talk to your vet before starting any supplement or therapy:

1. Diet Change

  • Feed only canned food, avoid dry kibble
  • Choose grain-free and potato-free canned foods
  • Avoid fish, seafood flavors with higher iodine
  • Reduce iodine by feeding homemade cooked diets

2. Chinese Herbs

Certain Chinese herbs may reduce thyroid hormones like:

  • Rehmannia root
  • Bugleweed
  • Motherwort
  • Dandelion leaf
  • Lemon balm

Research on safety and effectiveness is limited. Work with a vet experienced in using herbs.

3. Nutritional Supplements

  • Vitamin B complex – helps normalize metabolism
  • Melatonin – anti-thyroid effect in animals
  • Omega-3 fatty acids – support healthy metabolism

Always choose pet-safe doses and high-quality brands.

4. Acupuncture

Acupuncture performed by a licensed veterinary acupuncturist may help balance thyroid function long-term. It improves symptoms in some cats with hyperthyroidism.

Natural remedies may be less effective than conventional treatment. Monitor your cat closely even if trying natural methods.

Improving Quality of Life for Hyperthyroid Cats

Caring for a hyperthyroid cat can be challenging. Here are tips to nurture your sick kitty:

  • Feed smaller, more frequent high-calorie meals
  • Make food easily accessible to encourage eating
  • Assist with grooming if needed
  • Provide steps or ramps for easy furniture access
  • Use litter boxes with low sides or cut-out entrance
  • Limit stress and maintain routines
  • Give medications on time – don’t skip or stop
  • Check in frequently via phone or video while away
  • Pet, brush and talk to your cat often

With treatment, most hyperthyroid cats regain their strength and stabilize at a healthy weight after a few weeks or months. But even well-managed cats need extra care, patience and love.

Saying Goodbye: End of Life with Hyperthyroidism

Even with treatment, hyperthyroidism eventually proves fatal for most cats. As your cat declines you may wrestle with when to say goodbye. Quality of life is key:

Consider euthanasia when:

  • Your cat stops responding to medication and treatment
  • Weight and muscle loss progress despite large appetite
  • Vomiting or labored breathing are frequent
  • Your cat seems constantly stressed or in pain
  • They have trouble walking, jumping or using the litter box
  • Your vet confirms end stage heart failure or cancer

To make remaining time special:

  • Cuddle and pamper your cat as much as possible
  • Hand feed favorite treats and foods
  • Keep them warm using pet beds, blankets and your lap
  • Move food, water and litter box close together for easy access
  • Try natural supplements or therapies for comfort
  • Take pictures and make paw prints or other mementos

Saying farewell to your beloved cat is devastating. But take comfort in knowing you are releasing them from incurable suffering. Honor their life by opening your heart to another rescue cat when you are ready.

The Bottom Line on Hyperthyroidism in Cats

Left untreated, hyperthyroidism can rob your cat of their health, energy and quality of life. But cats diagnosed and managed early can live happily for years after developing thyroid disease.

By recognizing the warning signs, choosing the best treatment options, and adjusting care to meet your cat’s evolving needs, you have the power to significantly impact the outcome.

With a little detective work, you can catch an overactive thyroid quickly and work with your vet to help your kitty feel their best. Monitor all senior cats closely and don’t hesitate to run any unusual symptoms by your veterinarian promptly.

The most important takeaway? An early diagnosis of hyperthyroidism could literally save your cat’s life. With commitment and care from pet parents like you, kitties with thyroid disease can thrive and defy the odds.