Thyroxine for Dogs

Thyroxine is a synthetic hormone also known as the T4 and may be administered to canines that have a thyroid problem. Thyroxine administered in the right doses will increase the levels of thyroid hormones in the dog’s system to a normal. The thyroid hormones are needed for a normal metabolism and to distribute energy for the dog.

When Thyroxine Is Needed

Thyroxine is a synthetic hormone that is needed when the dog develops hypothyroidism or a low level of thyroid hormones in the body.

Hypothyroidism may appear at any age and will manifest through the following symptoms:

  • Weight gain
  • Dry, flaky skin
  • Coarse hair
  • Hair loss
  • Recurrent skin infections
  • Resistance to exercise


The dog needs to get a clear diagnosis to make sure he needs a thyroxine treatment. The dog may display similar symptoms when he is affected by allergies or has a ringworm infection. However, the weight gain is typically indicative of a hormonal problem.

Diagnosing Hypothyroidism

Hypothyroidism can be established through a blood test that will measure the levels of thyroid hormones in the body. The normal level of thyroid hormones depends on the dog’s age and breed.

Thyroxine Treatment

The thyroxine treatment is recommended when the levels of thyroid hormones are low. From all the thyroid hormone replacements, thyroxine is the most widely used in canines.

Thyroxine is available in the form of tablets, which are only available through prescription.

The dosage will be established by the vet, based on the dog’s thyroid levels, breed and weight. Typically, the medication should be given twice per day, which will ensure that the level of thyroid hormones stays constant during the day.

The effects of the treatment will be visible 3 to 5 days after starting the treatment, as it takes time for the body to recognize and assimilate the synthetic hormones.

The treatment is typically administered for several months; in some cases, the treatment will be for life. However, periodical tests (i.e. once per month) will be required to monitor the level of thyroid hormones and to determine if a change in dosage should be made.

Thyroxine Overdose

A thyroxine overdose is possible, especially if you don’t follow the guidelines of the vet or if the dog accidentally ingests more tablets.

The symptoms of a thyroxine overdose include:

  • Agitation
  • Vomiting
  • Increased thirst and appetite
  • Increased urination frequency
  • Irregular breathing
  • Irregular pulse
  • Increased heart rate

Seek veterinary advice as soon as you notice any of these symptoms.

Thyroxine Side Effects

Thyroxine may have a number of side effects, most importantly it can interfere with the normal thyroid hormonal production and the dog’s body may be used to getting the hormone, so the thyroid glands may stop producing these hormones altogether.

Other side effects may include hyperactivity, irritability and aggression.

Thyroxine may interact with other drugs (i.e. seizure medication), so let the vet know prior to getting the thyroxine prescription.