Last Updated: 17/12/2025
Hypothyroidism in Dogs: Signs, Causes and Treatment guide
Is your dog seeming sluggish or gaining weight? It could be an underactive thyroid. Our expert vet guide covers everything from common breed predispositions and diagnostic tests to medication and the best skincare diets to manage hypothyroidism.
Author: Dr Carla Paszkowski BVSc (Hons)
Reading Time: 7 minutes - short read
Finding out your canine companion has a chronic health condition can feel overwhelming, but a diagnosis of hypothyroidism is often the first step toward getting your pup’s spark back. This common hormonal imbalance occurs when the thyroid gland doesn't produce enough thyroxine, essentially slowing down your dog's internal motor. While it might sound serious, most dogs respond beautifully to simple daily management. Whether you’ve just received a diagnosis or are researching a breed prone to the condition, this guide will walk you through how to support your dog so they can get back to their happy, waggy self.
What is hypothyroidism in dogs?
Hypothyroidism is a condition in which the thyroid gland (a small gland with two lobes that sit around the trachea in the throat) is underactive in the dog's body. The thyroid gland normally produces thyroxine (T4) and triiodothyronine (T3), which are hormones that help regulate the body's metabolism. If the dog suffers from hypothyroidism these thyroid hormones are reduced or absent, which leads to problems with the skin, coat, energy levels, heat regulation, and immune system.
Did you know? Thyroid hormones are normally used by the body to regulate the metabolism, keep the body warm, fight infection, and maintain a healthy skin barrier. When thyroid hormones are not being produced properly, these body systems are disrupted and cannot function abnormally.
Dog breeds that are prone to Hypothyroidism
Hypothyroidism usually occurs in middle-aged dogs (aged 4-10) of medium to large sized dog breeds. Desexed dogs also have a higher risk. Particular breeds that are prone to developing hypothyroidism include:
- Retrievers including Golden Retrievers and Labradors
- Dobermanns
- Dachshunds
- Boxers
- Cocker Spaniels
- Miniature Schnauzer
- Irish Setters
Common causes of an underactive thyroid
Hypothyroidism is caused by disease or destruction of the tissue in the thyroid gland. The two most common processes that cause gland destruction are inflammatory and degenerative, as outlined below. These two causes make up approximately 95% of cases. Tumours of the thyroid gland are a rarer cause and may account for up to 5% of cases.
- Inflammatory destruction - lymphocytic thyroiditis. This is the most common cause and is thought to be immune-mediated. In this type of disease, the immune system attacks its own thyroid gland.
- Degeneration - idiopathic thyroid gland atrophy. This type of Hypothyroidism occurs when normal thyroid tissue is replaced by fat tissue. This root cause of this condition is poorly understood.
- Tumours of the thyroid gland. Thyroid tumours are rare but can cause hypothyroidism in up to 5% of dogs.
Signs of hypothyroidism to watch for
Hypothyroidism usually occurs in middle aged and senior dogs. Symptoms typically appear gradually over an extended period of time.
Clinical signs of Hypothyroidism include:
- Weight gain, often without an increase in appetite
- Puffy skin, known as the classic 'tragic' face
- Brittle or thinning fur, particularly over the torso, abdomen and tail
- Reduced energy, lethargy and listlessness
- Inability to stay warm - owners often notice their dog shivers or seeks heat more than they used to
- Chronic skin and ear infections
- Increased pigmentation of the skin
- Inability to grow hair back after shaving (shaving alopecia)
There are other less common, signs of hypothyroidism that occur occasionally. These include reproductive problems, nervous systems abnormalities such as nerve pain or dragging the hind legs, eye issues such as dry eye, and thickening of the facial skin which creates a droopy look.
How vets diagnose thyroid issues
Diagnosis of Hypothyroidism requires a veterinary examination and blood tests. Your vet will need to complete a full physical examination, and rule out any skin infections with a skin scrape and cytology test.
Blood Tests for Hypothyroidism
Your vet will likely run the following tests:
- Baseline bloodwork (CBC / biochemistry)
- Urinalysis
- Total thyroxine level - also known as Total T4 or TT4. This test measures your dog's main thyroid hormone level. If it is low, this can be suggestive of a diagnosis - however total thyroid hormone can also be low from other disease processes that depress the immune system.
- Free T4 / TSH (thyroid stimulating hormone) levels. A full thyroid panel which measures TSH and free T4 is usually done after a low TT4 level was observed, as it is a more accurate indicator for hypothyroidism.
TSH (thyroid stimulating hormone) is produced by the pituitary gland to stimulate the thyroid to produce T4 and free T4. In a dog with hypothyroidism, Total T4 and Free T4 will be low, while TSH will be high or normal.
Treatment and long-term management
While hypothyroidism cannot be cured, the good news is that it can be easily treated with an oral medication. However, your dog will need to be treated with the oral hormone replacement for life.
Medication for Hypothyroidism in Dogs
The standard treatment for hypothyroidism in dogs is daily oral administration of levothyroxine. This drug is a synthetic version of thyroid hormone. Giving thyroid hormone daily helps replace the circulatory thyroid hormone concentrations and reverses the disease. Ongoing care with regular vet check ups will be necessary to monitor your dog's progress and response to medication.
Did you know: treatment of hypothyroidism simply involves replacing the hormone that is low or absent, just like hormone replacement therapy in menopausal women.
Home Care for a Dog with Hypothyroidism
In addition to giving your dog their medication daily, you will need to monitor your dog's skin and body weight to detect any changes. If the clinical signs disappear and your dog gets their appetite back, this is a good sign and means the medication is working. It's also important to feed your dog an appropriate food and limit treats and table scraps - read more about this below.
The best diet for dogs with hypothyroidism
Unlike other conditions such as Kidney disease or Diabetes, a strict Prescription Diet is not required for Hypothyroidism. Most high quality adult diets - particularly those formulated for skin care - will meet the above criteria and keep your hypothyroid dog nourished and healthy.
Many dogs with hypothyroidism benefit from a skin care diet to help with any concurrent skin problems. Your vet may recommend a specific diet
As your dog begins to get their appetite and metabolism back with treatment, they may beg for treats and tidbits more. It is important not to give into the temptation to over treat them - and therefore limit treats, table scraps, and snacks, particularly those that are high in fat, salt, or sugar. Stick instead to healthy treats such as regular kibble, carrots, apples, or strawberries.
Please note: the above recommendations are general advice only. Your vet may recommend a Veterinary-Prescribed Dog Food if they feel that other health issues are present. See our article on Prescription Diets for Pets for more information.
Supplements for skin and coat health
Supplements are generally not required if you are providing your dog with a balanced adult diet from a vet-recommended brand (like one of the diets recommended above). However, hypothyroidism can create dry skin and dull fur, which can benefit from a number of nutrients supplemented, including:
1. Fish oil / omega fatty acids can help improve dull fur or inflamed skin, and strengthen the skin barrier.
2. Vitamins A, C and E can also help strengthen the skin barrier and promote a stronger immune system.
3. Zinc has antiinflammatory effects - particularly on collagen production, fatty acid metabolism and wound healing.
FAQs
While a diagnosis of hypothyroidism means lifelong monitoring, it is one of the most manageable conditions we see in the clinic. With a consistent medication routine and a high-quality diet tailored to their skin health, most dogs return to their normal energy levels and regain their beautiful coats in no time. If you notice any changes in your dog's weight or energy, always check in with your vet - catching it early makes all the difference.
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History
Our experts continually monitor the health and wellness space and we update our articles when new information becomes available.
Thu 18 Dec 2025
Edited by Dr Gillian Hill BVSc (Hons)Dr Carla Paszkowski BVSc (Hons)
Veterinarian
Dr. Carla graduated from the University of Queensland in 2013 with a Bachelor of Veterinary Science and worked for a number of years in small animal clinics across South East Queensland. While Carla enjoys most facets of clinical veterinary work, she holds a special passion for feline medicine, pocket pets, and nutrition.
