Hypothyroidism in dogs


  • Hypothyroidism is a lack of thyroid hormones due to underactive thyroid glands.
  • Symptoms of hypothyroidism include weight gain, low energy, and fur loss (alopecia).
  • Hypothyroidism is treated using daily medication to replace the missing thyroid hormones.
  • With treatment, the outlook for a dog with hypothyroidism is excellent.
  • Contact your vet if your dog is showing signs of hypothyroidism.

Hypothyroidism explained

The thyroid glands are two small glands that sit in the neck, close to the windpipe.

They produce thyroid hormones that are used all around the body.

Hypothyroidism is a condition that develops when the thyroid glands become underactive and don’t produce enough thyroid hormones.

Hypothyroidism is the opposite of hyperthyroidism – a condition caused by overactive thyroid glands producing too much thyroid hormone (common in cats but very rare in dogs).

Illustration showing thyroid glands in dogs

Thyroid glands in a dog


It’s often difficult to find out why a dog has developed hypothyroidism, but we know it’s most commonly caused when the immune system accidentally attacks and damages the thyroid glands.


Symptoms of hypothyroidism are usually vague and develop gradually; common signs include:

Dog with fur loss on sides and tail

This dog has fur loss on his sides and tail due to hypothyroidism.

When to contact your vet

Contact your vet if you think your dog may be showing signs of hypothyroidism.


Hypothyroidism is diagnosed using blood tests that detect the low thyroid hormone levels. General illness can also cause a drop in thyroid levels, so your vet will want to check your dog thoroughly, and rule out any other problems before starting treatment.


If your dog has hypothyroidism, they will need medication (usually a tablet), for the rest of their life. Their medication will replace the thyroid hormones they are missing.

How to give your dog a tablet

Natural treatments and home remedies

The best way to treat hypothyroidism is with medication from your vet. There are no proven natural remedies or home treatments for hypothyroidism. Speak to your vet for more information.

Outlook and ongoing care


With successful treatment, your dog’s outlook is excellent. As long as they stay on treatment, they can live a long, happy life without symptoms.

How long does thyroid medicine take to work?

Your dog should seem happier and more energetic within a couple of weeks. They may lose more fur to begin with but don’t worry, this is normal, it should start to regrow within 4-6 weeks. They should be looking slimmer and healthier within 3 months and be back to normal within 6 months.


Your dog will need regular vet checks, and you will need to monitor for any new symptoms. Your vet may perform repeat blood tests to ensure your dog’s thyroid hormones are staying at the right level.

Breeds at risk

The following breeds are at a higher risk of hypothyroidism:


What happens if hypothyroidism is left untreated?

If you leave your dog’s hypothyroidism untreated, they will continue feeling poorly and their symptoms will get worse. Eventually severe complications will develop which may lead to death.

What’s the difference between ‘hypothyroidism’ and ‘hyperthyroidism’?

  • Hypothyroidism = low levels of thyroid hormone (common in dogs, rare in cats).
  • Hyperthyroidism = high levels of thyroid hormone (common in cats, rare in dogs).

What’s the best dog food for hypothyroidism?

Hypothyroidism nearly always causes weight gain in dogs. However, once your dog has started treatment, their metabolism will return to normal and they will lose those extra pounds. It’s unlikely you will need to change your dog’s diet.


Treatment for a chronic condition such as hypothyroidism can become very expensive over time. Consider insuring your dog as soon as you get them, before any signs of illness start. This will ensure you have all the support you need to care for them.

It’s also very important to speak openly to your vet about your finances, the cost of treatment, as well as what you think is right for your dog. There are often several treatment options so if one doesn’t work for you and your pet then the vet may be able to offer another.

Published: August 2019

Written by vets and vet nurses. This advice is for UK pets only. Illustrations by Samantha Elmhurst.