Does your dog seem sluggish, gaining weight, or losing fur? These could be signs of hypothyroidism, one of the most common hormonal disorders in dogs. 

The thyroid gland plays a crucial role in metabolism, energy levels, and skin health. When it doesn’t produce enough thyroid hormone, your dog’s body slows down—leading to a wide range of symptoms. The good news? It’s manageable with lifelong treatment. 

What Is Hypothyroidism? 

Hypothyroidism occurs when the thyroid gland (located in the neck) fails to produce enough thyroid hormones—specifically T3 and T4. These hormones regulate metabolism, skin health, and energy levels. 

Causes of Hypothyroidism: 

• Primary hypothyroidism (most common – 90% of cases): 

• Lymphocytic thyroiditis – an autoimmune disease (similar to Hashimoto’s in humans) 

• Idiopathic atrophy – where thyroid tissue is replaced with fat 

• Congenital hypothyroidism (rare): A birth defect where the thyroid gland doesn’t form properly 

• Secondary hypothyroidism (rare): The pituitary gland fails to produce Thyroid Stimulating Hormone (TSH), which tells the thyroid gland to function 

Signs and Symptoms of Hypothyroidism in Dogs 

Because the thyroid gland controls metabolism, low thyroid hormone levels affect nearly every system in the body. 

Common symptoms include: 

• Weight gain (even with no change in diet) 

• Lethargy & low energy – your dog may seem sluggish or sleep more than usual 

• Cold intolerance – your dog prefers warm places or shivers easily 

• Mental dullness – your dog seems less alert or responsive 

• Slow heart rate (bradycardia) 

Skin & coat changes: 

• Hair loss (alopecia), often on the tail, nose, or pressure points 

• Dull, dry, brittle coat – fur may become thin and rough 

• Hyperpigmented skin – darkening of the skin 

• Slow hair regrowth – after being shaved or clipped 

• Chronic skin infections – including bacterial and yeast (Malassezia) overgrowth 

• Ear infections (ceruminous otitis externa) 

Less common neurological signs: 

• Weakness or muscle loss 

• Seizures or ataxia (wobbly walking) 

• Facial nerve paralysis (drooping of the face, head tilt) 

If your dog is showing multiple symptoms, talk to your vet about thyroid testing. 

Which Dog Breeds Are at Higher Risk? 

Hypothyroidism can affect any dog, but some breeds are more prone than others: 

• Golden Retrievers 

• Labrador Retrievers 

• Doberman Pinschers 

• English Bulldogs 

• Shar Peis 

• Chow Chows 

• Dachshunds 

• Pomeranians 

• Shetland Sheepdogs 

Most cases are diagnosed between 6–10 years old, but it can develop earlier in young large-breed dogs. 

How Is Hypothyroidism Diagnosed? 

Your vet will perform blood tests to measure thyroid hormone levels. 

Key blood tests include: 

• Total T4 (TT4): A low T4 suggests hypothyroidism, but this test alone isn’t enough 

• Free T4 (FT4): More reliable than TT4, as it measures the active hormone 

• TSH (Thyroid-Stimulating Hormone): High TSH with low T4 confirms hypothyroidism 

Other findings that support diagnosis: 

• High cholesterol & triglycerides 

• Mild anemia (low red blood cell count) 

Important Note: Some medications—like steroids or anti-seizure drugs—can lower T4 levels, leading to false positives. Always interpret results alongside clinical signs. 

Treating and Managing Hypothyroidism in Dogs 

The good news? Hypothyroidism is easily managed with medication. 

Treatment: Levothyroxine (Thyroid Hormone Replacement) 

• Dosage: 0.02 mg/kg twice daily (adjusted as needed) 

• Recheck bloodwork in 4–6 weeks after starting treatment 

What to Expect After Starting Treatment 

• 7–14 days: Increased energy and appetite 

• 4–6 weeks: Skin starts improving, old hair is shed, and new hair begins to grow 

• 3 months: Coat returns to normal, skin conditions resolve, and weight stabilizes 

If your dog isn’t improving, your vet may need to adjust the dose or investigate other conditions like Cushing’s disease. 

Managing Hypothyroidism in Dogs 

With proper treatment, hypothyroid dogs can live long, healthy lives. 

• Give medication consistently – the dose must be given every day for life 

• Regular bloodwork checks – ensure your dog is on the correct dose 

• Monitor weight and coat health – watch for improvement or signs of under/overmedication 

When to See Your Veterinarian

If your dog is gaining weight, losing fur, or slowing down, don’t assume it’s just aging—it could be hypothyroidism. 

At Boundary Bay Veterinary Specialty Hospital, our board-certified internal medicine specialists are specially trained to diagnose and manage complex endocrine disorders like hypothyroidism. Our team uses advanced diagnostic tools to provide accurate diagnoses and personalized treatment plans for your dog. We also work closely with your primary care veterinarian to ensure continuity of care. 

If you suspect your dog may have hypothyroidism, speak with your family veterinarian or contact our Internal Medicine service directly to schedule a consultation. Early diagnosis and treatment lead to better outcomes and a healthier life for your dog. 

Original presentation written by: Sarah Charney, DVM, DACVIM, DACVR