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Key facts

  • Hypothyroidism (underactive thyroid) occurs when the thyroid gland does not make enough thyroid hormone.
  • Symptoms are varied but can include fatigue, weight gain, heavy periods or sensitivity to the cold.
  • The most common cause of hypothyroidism in Australia is the autoimmune disease, Hashimoto's disease.
  • Hypothyroidism is often treated with a synthetic version of the hormone thyroxine.

What is hypothyroidism (underactive thyroid)?

Hypothyroidism (underactive thyroid) is a medical condition where the thyroid gland does not make enough thyroid hormone.

The thyroid gland is located in the neck, near the base of the throat. It makes hormones that help control some of your body’s metabolic processes, such as heart rate, blood pressure, body temperature and weight.

What are the symptoms of hypothyroidism (underactive thyroid)?

Hypothyroidism (underactive thyroid) can develop over many years without showing any symptoms. When symptoms do appear, they may be varied and can include:

Some people can have symptoms of hypothyroidism without any abnormality in their hormone levels. At other times, these symptoms may have different causes. If you are concerned about any of these symptoms, see your doctor.

What causes hypothyroidism (underactive thyroid)?

The most common cause of hypothyroidism in Australia is Hashimoto's disease, or thyroiditis. This is an autoimmune disease that occurs when the body’s immune cells attack the thyroid gland.

Other common causes of hypothyroidism include:

It can also be caused by too little iodine in the diet, a problem with the pituitary gland, or by pregnancy.

How is hypothyroidism (underactive thyroid) diagnosed?

Your doctor will check your neck to see if your thyroid is enlarged or has nodules, and will look for other signs of hypothyroidism (underactive thyroid), such as a slow heart rate.

To diagnose hypothyroidism, they will do a blood test to measure the level of your thyroid hormones.

How is hypothyroidism (underactive thyroid) treated?

If you are diagnosed with hypothyroidism (underactive thyroid), you will most likely be treated with a medicine to replace the thyroid hormone. This medicine is a synthetic version of the hormone thyroxine, and in most cases you will need to take it for the rest of your life.

Once treatment has begun, it may take some time to get the dose right for you. Further adjustments may be needed as time goes by, so your hormone levels will need to be checked regularly.

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Last reviewed: November 2020

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