Hypothyroidism in Dogs: A Veterinary Discourse by Catherine Barnette, DVM, Reviewed by Emily Oliver, CVT on July 31, 2025, and Published on July 21, 2023. Shared via Facebook, Twitter, Email, and Print Media.
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In the canine world, hypothyroidism – a condition characterized by abnormally low levels of circulating thyroxine – is relatively common, particularly in middle-aged and older dogs. This article provides an overview of the symptoms, causes, diagnosis, treatment, and management of hypothyroidism in dogs.
Symptoms
The symptoms of hypothyroidism in dogs can be vague and may include weight gain, lethargy, hair loss, a dull or brittle coat, darkening of the skin, vomiting, diarrhea, ocular changes, facial nerve paralysis, changes in heart/lung function, and pacing and restlessness. Affected dogs, especially overweight ones, often lose excess weight once their thyroid hormone levels are corrected.
Causes
Hypothyroidism can be divided into congenital (inherited) and acquired forms. Congenital hypothyroidism, though rare in dogs, is caused by a mutation in the genes and can be prevented by avoiding breeding pets with this condition. Acquired hypothyroidism, on the other hand, is the most common form and is often caused by an autoimmune reaction within the thyroid gland.
The most frequent cause of acquired hypothyroidism in dogs is autoimmune thyroiditis, an inflammation of the thyroid gland leading to its destruction. Another cause is thyroid gland atrophy, where the gland gradually shrinks and loses function. Acquired hypothyroidism can occur in any dog, including both purebred and mixed breed dogs.
Diagnosis
Diagnosis of hypothyroidism in dogs involves a blood test measuring thyroid hormones (total T4) and thyroid stimulating hormone (TSH). Low T4 combined with high TSH indicates primary hypothyroidism, meaning the thyroid gland is failing to respond to pituitary signals. Because thyroid levels can be influenced by other illnesses or medications, veterinary assessment is essential.
Treatment
Treatment for hypothyroidism in dogs involves a synthetic thyroxine supplement, administered orally. The starting dose is calculated based on a dog's weight and current thyroid levels. Treatment helps reverse symptoms, although side effects such as increased thirst, urination, appetite changes, or occasional vomiting or diarrhea can occur and should be monitored closely.
Management
One month after starting treatment, a dog's Total T4 level is assessed to determine if a dose adjustment is needed. The cost of levothyroxine treatment for dogs is typically between $20-$50 per month, and thyroid testing, usually performed once or twice yearly, costs $50-$100. With consistent treatment, dogs with hypothyroidism can lead normal, healthy lives.
In summary, hypothyroidism in dogs is a manageable condition with proper veterinary care and lifelong hormone therapy. Early detection improves quality of life for affected dogs.
