Health conditions

Hypothyroidism (underactive thyroid)

What is hypothyroidism?

Hypothyroidism is a health condition characterised by unusually low hormone production.

It is when your thyroid gland becomes underactive and cannot produce enough hormones to regulate your metabolism.

If your thyroid can’t secrete enough hormones into your bloodstream, your body’s metabolism slows down rapidly.

Hypothyroidism is the most common thyroid disorder in Australia, and mainly affects women over 40.

There are 2 types of hypothyroidism:

  • primary hypothyroidism – when your thyroid gland becomes diseased and cannot produce sufficient hormones
  • secondary hypothyroidism – when your pituitary gland isn’t stimulating your thyroid to produce enough hormones.

Terms explained

Autoimmune disorder – a condition where your own antibodies attack your body.

Causes of hypothyroidism

There are various causes of hypothyroidism, including a diet low in iodine, and this condition is often the result of thyroid surgery.

Another cause of primary hypothyroidism is an autoimmune condition called Hashimoto’s thyroiditis.

This disorder is caused when antibodies from your immune system destroy your thyroid gland cells and prevent your body producing enough hormones.

Hashimoto’s thyroiditis can also cause goitre, a condition that substantially enlarges your thyroid gland.

Other causes include:

  • congenital hypothyroidism
  • some hyperthyroidism (overactive thyroid gland) treatments can trigger hypothyroidism including:
    • radio-iodide therapy
    • anti-thyroid medication
    • surgery
  • brain disorders specifically affecting the hypothalamus connecting your nervous and endocrine systems
  • pituitary gland or hypothalamic dysfunction.

Signs and symptoms of hypothyroidism

Hypothyroidism develops gradually and slows down your metabolism.

The symptoms can range from mild to severe and include:

  • depression, feeling withdrawn and a lack of motivation
  • inability to concentrate
  • body fatigue, muscle aches and low energy levels
  • needing more sleep
  • intolerance to cold temperatures
  • unexplained weight gain
  • dry skin and /or pale skin and facial bloating
  • hair loss or thinning out
  • constipation
  • heavy, irregular or prolonged menstrual periods
  • goitre (enlarged thyroid gland that is visible)
  • slower heart rate.

Diagnosis of hypothyroidism

Thyroid conditions can easily be misdiagnosed as symptoms are similar to a range of other health conditions. 

Hypothyroidism is diagnosed by thyroid function tests, blood tests and a medical examination.

Diagnosis is made by monitoring the levels of Thyroid Stimulating Hormone (TSH) and types of antibodies found in your blood.

Treatment of hypothyroidism

The symptoms of hypothyroidism can get significantly worse if they remain undiagnosed and untreated.

There is no cure for autoimmune hypothyroidism and the condition is treated with lifelong hormone replacement tablets containing thyroxine.

Your doctor will initially place you on a lower dose of thyroxine that is adapted according to the data from your blood tests. You are likely to need an annual thyroid function test.

It’s important to take the correct dose of medication as advised by your doctor. If you take too much thyroxin it could cause hyperthyroidism, an overactive thyroid condition.

Symptoms of hyperthyroidism include:

  • unexplained weight loss
  • heat sensitivity
  • heart palpitations and rapid heart rate
  • diarrhoea
  • increased perspiration
  • anxiety and irritability.

If left untreated

If hypothyroidism symptoms are severe, remain ongoing and are left untreated, the condition can develop into a rare and potentially fatal disorder known as myxoedema coma.

Hyperthyroidism – an overactive thyroid

People with hypothyroidism will need to take medication for the rest of their life as there is no cure. The dose taken must be accurate.

If you have too much thyroxin in your body from your medication you may get hyperthyroidism – an overactive thyroid which could lead to more serious health implications.

Where to get help

  • See your doctor
  • Visit a GP after hours
  • See your endocrinologist
  • Ring healthdirect Australia on 1800 022 222


  • The hormones your thyroid gland produce help control your metabolism.
  • Hypothyroidism is when your thyroid gland doesn’t secrete enough hormones into your bloodstream.
  • A diet low in iodine is the leading cause of hypothyroidism.
  • Treatment involves lifelong hormone replacement with thyroxine tablets.


Diabetes and Endocrine Health Network

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.