Symptoms of hypothyroidism in dogs: Key signs to spot

The thyroid glands, located on either side of your dog’s neck, play a vital role in regulating metabolism, hormones, and nutrient absorption. They also influence appetite, healthy weight, and overall digestive health. When these glands don’t function correctly, it can lead to hypothyroidism, a condition where the thyroid underproduces hormones, disrupting your dog's bodily systems and causing various symptoms.

Recognising hypothyroidism early is key to effective treatment and improving your dog's quality of life. Below, we explain the main symptoms to watch for if you suspect your dog may have an underactive thyroid gland.

1. Lethargy and reduced activity

Hypothyroid dogs often show marked lethargy, lacking their usual energy and enthusiasm. This symptom develops gradually, with affected dogs showing less interest in play and exercise, tiring quickly even on short walks. They may sleep more and respond slower to stimuli.

2. Increased thirst and urination

Hormonal imbalances caused by hypothyroidism can increase your dog’s thirst, leading to excessive water intake. This, in turn, results in more frequent urination, which may include accidents indoors if the dog cannot access the toilet quickly.

3. Unexplained weight gain

One hallmark of hypothyroidism is weight gain that occurs even without an increase in food intake. The slowing of metabolism means calories are not efficiently converted into energy but stored as fat instead, making weight management difficult.

4. Changes in skin texture and condition

Hypothyroidism often causes dry, flaky, or fragile skin. Your dog’s skin may feel papery or brittle and become prone to infections or irritations, including chronic conditions like pyoderma or ear infections. Sometimes, the skin appears greasy even after bathing.

5. Fur loss and coat changes

Hair loss, especially in symmetrical patches along the flanks and base of the tail (sometimes called "rat tail"), is a common sign. The coat often becomes dull, coarse, and fails to regrow properly after shaving or clipping.

6. Increased skin pigmentation and thickening

Many hypothyroid dogs develop areas of darker skin (hyperpigmentation) and thickened skin, adding to the abnormal skin appearance and texture changes.

7. Nerve or muscle issues in advanced cases

If untreated, hypothyroidism may cause neurological symptoms like hind limb weakness, difficulty walking, or altered behaviour due to nerve damage. Facial muscle drooping and dry eyes from reduced tear production may also occur.

8. Risk of serious complications if untreated

Untreated hypothyroidism can lead to severe obesity, chronic infections, muscle wasting, immune dysfunction, infertility, and in rare cases, life-threatening myxoedema coma. Early veterinary diagnosis using blood tests and prompt treatment with synthetic thyroid hormones are vital for a positive outcome.

Hypothyroidism is much more common than an overactive thyroid (hyperthyroidism) in dogs and typically affects middle-aged, medium to large breeds. If you observe several of the above symptoms, please consult your vet promptly. Responsible pet ownership means monitoring your dog’s health and acting swiftly to ensure their well-being.

Maintaining a routine health check with your vet will help to catch thyroid or other health issues early, supporting your dog's long, happy life.