Cats are masters of subtlety. They curl into quiet corners when they’re not feeling well, sleep a little longer, eat a little less or more, and rarely raise alarm bells. But what if those small changes are actually your cat’s body crying out for help?

Hypothyroidism in cats is rare, but when it does occur, it affects everything from energy levels to organ function. And if you’re living in a place like the UAE, where heat and dehydration already strain your cat’s system, an underactive thyroid can quietly wreak havoc.

At Noble Vet Clinics, we’ve seen firsthand how easily this condition can be overlooked and how dramatically life improves when it’s treated early. Let’s explore the facts, the science, and the signs you shouldn’t ignore.

What Is Hypothyroidism in Cats, and How Rare Is It?

Hypothyroidism is a condition where the thyroid gland fails to produce enough thyroid hormones, primarily thyroxine (T4). This hormone regulates metabolism, energy, and body temperature. 

In cats, hypothyroidism is far less common than hyperthyroidism, the latter being an overproduction of these hormones.

But make no mistake: just because it’s rare doesn’t mean it’s harmless. The condition is often either congenital (present from birth) or iatrogenic, which means it’s caused by medical treatment, most often for hyperthyroidism.

According to the Merck Veterinary Manual, feline hypothyroidism is most frequently seen after radioactive iodine therapy, surgical thyroidectomy, or long-term methimazole use. These treatments suppress the thyroid to correct an overactive state, but occasionally, they suppress it too much.

In hot, arid climates like Dubai and Abu Dhabi, where your cat’s metabolism is already adapting to environmental stressors, the symptoms can quietly intensify.

What Triggers Hypothyroidism in Cats?

The two primary causes of feline hypothyroidism are:

Congenital Hypothyroidism

This form is exceptionally rare and typically seen in kittens. It results from abnormal thyroid development or hormone production from birth. These cats often show stunted growth, a dull coat, and a sad kind of lethargy that’s hard to miss once you recognize it.

Iatrogenic Hypothyroidism

By far the more common scenario, this occurs in adult cats as a result of overtreatment for hyperthyroidism. Procedures like thyroid gland removal, radioiodine therapy, or even medication (methimazole) may tip the balance too far, reducing hormone production below healthy levels.

In some cases, the hypothyroidism may resolve on its own. In others, lifelong treatment is necessary.

What Are the Signs of Hypothyroidism in Cats?

Because hypothyroidism in cats is so uncommon, symptoms often mimic other conditions, or worse, are dismissed as part of “getting older.”

Here are some red flags to watch for:

• Unexplained weight gain

• Lethargy or lack of interest in play

• Low body temperature

• Dry, thinning coat or excessive shedding

• Constipation

• Mental dullness or "zoned out" behavior

• Slow heart rate (bradycardia)

• Sensitivity to cold

• Swelling in the neck (goiter)

In our UAE climate, these symptoms may be even more subtle. Your cat might simply seem “off” or extra sleepy. That’s why bloodwork is key.

How Is Hypothyroidism in Cats Diagnosed?

Diagnosing hypothyroidism requires precise blood tests. We look at:

• Total T4 levels: Often low in hypothyroid cats

• Free T4 by equilibrium dialysis (FT4ED): More sensitive than total T4

• Thyroid Stimulating Hormone (TSH): Elevated when thyroid hormone is low

• Thyroid panels: To rule out other metabolic imbalances

It’s important to test more than once. Hormone levels can fluctuate, and some cats (especially those post-hyperthyroid treatment) may have transient hypothyroidism.

At Noble Vet Clinics, we perform both in-house diagnostics and consult with external endocrinologists when cases require more in-depth investigation. Your cat’s health deserves nothing less.

Is Feline Hypothyroidism Dangerous If Left Untreated?

Yes. An untreated thyroid imbalance can lead to organ dysfunction, particularly involving the heart and kidneys. In kittens, it can severely stunt growth and brain development. In adults, it slowly depletes vitality, reducing quality of life, day by day.

In desert climates like the UAE, cats with slowed metabolism are also more prone to heat intolerance and dehydration. So while the condition isn’t an immediate emergency, its long-term effects can be devastating if overlooked.