What is hypothyroidism (underactive thyroid)?

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

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.

While some people have underactive thyroids, others have overactive thyroids (hyperthyroidism). This condition has different causes, symptoms and treatments.

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 vary from person to person.

Some symptoms affect your appearance, for example:

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

Other symptoms affect how you feel, for example:

• tiredness
• being unable to tolerate the cold
• muscle pain
• constipation
• headache
• slow heart rate
• heavier than normal periods

Symptoms may also affect how you think, for example, hypothyroidism can also affect your:

• memory
• attention span
• mood (depression)

Some people can have symptoms of hypothyroidism without any abnormality in their hormone levels. These symptoms may have different causes other than hypothyroidism.

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:

• surgery that removes some or all of the thyroid
• radiation therapy
• treatment for an overactive thyroid (hyperthyroidism)
• some medicines, including lithium

Hypothyroidism can also be a result of too little iodine in the diet, or a problem with the pituitary gland, or occasionally, pregnancy.

How is hypothyroidism (underactive thyroid) diagnosed?

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

To diagnose hypothyroidism, your doctor will order a blood test to measure your level of 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 (artificial) version of the hormone thyroxine. In most cases, you will need to take it for the rest of your life.

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.

What are the complications of hypothyroidism?

If untreated, hypothyroidism can lead to a range of health problems including:

• obesity
• infertility
• joint pain
• heart disease

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

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

How is hypothyroidism prevented?

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

You can prevent hypothyroidism caused by iodine deficiency by ensuring you include iodine in your diet. An easy way to do this is by cooking with iodised salt, and using iodised table salt. These are 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.

Resources and support

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