What is hypothyroidism?

Hypothyroidism (underactive thyroid) is a health condition where your thyroid gland does not make enough thyroid hormone for normal body function.

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

Some people have an overactive thyroid. This is called hyperthyroidism. This condition has different causes, symptoms and treatments.

What are the symptoms of hypothyroidism?

Hypothyroidism can develop over many years without showing any symptoms. Hypothyroidism slows down your metabolism. When symptoms do appear, they may vary from person to person. Symptoms become more severe as your thyroid function decreases.

Some symptoms affect your appearance, such as:

• unexplained weight gain
• puffy and pale face
• brittle hair and nails
• thinning hair
• dry, cool skin

In some cases, your thyroid gland may be visibly enlarged (this is called a goitre).

Other symptoms affect how you feel, such as:

• tiredness
• being unable to tolerate the cold
• muscle pain
• constipation
• headache
• shorter attention span than usual
• low mood, depression or lack of motivation

Hypothyroidism can also result in irregular or heavier than normal periods. You may also have difficulty becoming pregnant.

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What causes hypothyroidism?

The most common cause of hypothyroidism in Australia is Hashimoto's disease, also known as Hashimoto’s thyroiditis. This is an autoimmune disease that happens when your body’s immune system makes antibodies (specific blood proteins) that attack your thyroid gland.

Other causes of hypothyroidism include:

• surgery that removes some or all of the thyroid
• radiation therapy
• treatment for an overactive thyroid (hyperthyroidism)
• some medicines, such as lithium
• genetic disorders
• not including enough iodine in your diet

Hypothyroidism is sometimes linked with pregnancy.

Thyroid conditions are more common in females than in males.

When should I see my doctor?

See your doctor if you have any symptoms of hypothyroidism. Many people live with an undiagnosed thyroid disorder. It can be hard to diagnose due to many symptoms being similar to those of other health conditions.

Be sure to let your doctor know about:

• your symptoms
• your family history
• any medicines or supplements that you are taking
• any member of your family who has previously had an autoimmune or thyroid condition

If you are taking medicine for hypothyroidism, see your doctor if you notice new symptoms or if your symptoms get worse. This might be a sign that your doctor needs to change your dose.

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How is hypothyroidism diagnosed?

Your doctor will ask you questions about your health and family history. They may examine your neck to check if your thyroid is enlarged or has nodules (lumps). They will also look for other signs of hypothyroidism, such as a slow heart rate.

To diagnose hypothyroidism, your doctor will refer you for a blood test. This test measures your level of thyroid hormones and to check if you have thyroid antibodies.

Sometimes your blood test might show mild levels of hypothyroidism. This is known as subclinical hypothyroidism. Your doctor will discuss this with you to decide if you need treatment.

More information about subclinical hypothyroidism is available on the Royal Australian College of General Practitioners’ (RACGP) website.

Sometimes babies are born with hypothyroidism. This is diagnosed on the newborn bloodspot screening test (sometimes called the ‘heel prick test’).

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How is hypothyroidism treated?

If your doctor diagnoses hypothyroidism, you will most likely need medicine to replace thyroid hormone. This medicine is designed to be similar to the hormone thyroxine.

In most cases, you will need to take it for the rest of your life. This medicine is usually taken once a day, at least half an hour before you eat breakfast.

Living with hypothyroidism

If you are taking thyroid hormone replacement therapy, it is important to continue taking your medicine even when your thyroid hormone levels return to a normal range and you are feeling better.

Once you have started treatment, you may need to have your hormone levels checked regularly so your doctor can adjust your dose. It can take some time to find the right dose of medicine for you.

When being treated for hypothyroidism, there is a risk that you may develop hyperthyroidism. This can happen if your levels and dose are not monitored closely by your doctor.

If your symptoms don’t go away with thyroid hormone replacement therapy, it may be due to other health problems. Talk to your doctor if you aren’t feeling better. They may refer you to an endocrinologist.

What are the complications of hypothyroidism?

If untreated, symptoms can get worse gradually, as your thyroid function gets worse.

Hypothyroidism can lead to a range of health problems including:

• high cholesterol
• decreased fertility
• problems with thinking
• depression
• heart disease
• a severe type of hypothyroidism called myxoedema coma — this is very rare

Children and teenagers with untreated hypothyroidism can have problems with growth and development.

If you are pregnant, untreated hypothyroidism increases your risk of miscarriage and other pregnancy complications.

Can hypothyroidism be prevented?

Most types of hypothyroidism can’t be prevented, but the symptoms can be managed.

You can prevent hypothyroidism caused by iodine deficiency by including iodine in your diet. An easy way to do this is by using iodised salt in cooking, and when adding salt to food. This is available at supermarkets.

If your hypothyroidism is caused by a medicine, speak to your doctor about changing it. Don’t stop any medicines without checking first with your doctor.

If you are planning a pregnancy, you should take an iodine supplement daily. Speak with your doctor about supplements and medicines that are safe to take while planning a pregnancy.

Resources and support

The Australian Thyroid Foundation offers further information on definitions, causes, conditions and treatments, as well as questions to ask your doctor.

Call the healthdirect helpline on 1800 022 222 at any time to speak to a registered nurse (known as NURSE-ON-CALL in Victoria) for more information and advice about thyroid disorders or thyroid medicines.

Do you prefer to read in languages other than English?

Hormones Australia provides information in community languages on thyroid conditions.

Looking for information for Aboriginal and/or Torres Strait Islander people?

Find an Aboriginal Community Controlled Health Organisation (ACCHO) or affiliate near you.