Hypothyroidism in Dogs

Hypothyroidism is one of the most common endocrine disease in dogs. We look at what causes it, when to suspect it and how it is treated.

Hypothyroidism (meaning abnormally low levels of thyroid hormones) is a condition found commonly in dogs but rarely in cats. It often affects large breeds, such as Labradors, Golden Retrievers, Boxers and Dobermanns, who are middle-aged onwards (4 years plus). 

What is hypothyroidism?

Hypothyroidism is a condition caused by an underactive thyroid gland (located in the neck) which is not producing enough thyroid hormone. Thyroid hormones are responsible for controlling the dog’s metabolism, and a fall in levels will affect almost all of the body. 

Causes of hypothyroidism

The most common cause is thought to be immune-related – the dog’s own immune system starts to create antibodies that attack the normal thyroid hormones. In other cases, the thyroid gland gradually shuts down over time and is replaced by inactive fat cells. Rarely the thyroid gland can also be destroyed by a tumour, causing hypothyroidism signs.  

Symptoms of hypothyroidism

Dogs suffering from hypothyroidism often have vague symptoms which develop gradually over time. 

The most common symptoms which can develop are:

  • Weight gain, or the inability to lose weight
  • Flaky, dry or greasy skin
  • Patchy hair loss, usually on sides of the body and tail
  • Lethargy, dullness
  • Tragic expression caused by a puffy face and thickening of the skin around the head
  • Skin infections due to a poor immune system
  • Appears colder than usual (seeking out heat or shivering)
  • A slow heart rate
  • Fat deposits in the eyes


A consultation with a veterinary surgeon is the first step to diagnosis. Usually, a full physical examination will need to be performed to rule out any other illnesses and a blood sample will be taken as a health screen and to measure the circulating thyroid hormone levels. 


Treating your dog usually involves artificial thyroid hormones given daily in the form of a tablet or liquid for the rest of their life. The appropriate dose for each dog varies, so sometimes repeat blood tests are needed to ensure the dose prescribed is correct. The good news is that the majority of dogs respond very well to treatment and most clinical signs resolve over the first few weeks to months of treatment. Dogs with well-managed hypothyroidism have an excellent prognosis and a normal life expectancy. 

How can VetontheNet help you?

The VetontheNet team is here to help at any time. Your dog may have already been diagnosed, or you may be concerned about clinical signs which could be related to hypothyroidism. We can offer video consultation with one of our friendly veterinary surgeons to take time to discuss any concerns you may have at a time that suits you – and your dog!