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Overview - Underactive thyroid (hypothyroidism)

An underactive thyroid gland (hypothyroidism) means your thyroid gland is not producing enough hormones.

Common signs of an underactive thyroid are tiredness, weight gain and feeling depressed.

An underactive thyroid can often be treated by taking hormone tablets. These are used to replace the hormones your thyroid is not making.

There's no way of preventing an underactive thyroid.

Most cases are caused either by:

  • the immune system attacking the thyroid gland and damaging it
  • damage to the thyroid during treatment for an overactive thyroid or thyroid cancer

Find out more about the causes of an underactive thyroid

When to see your GP

Symptoms of an underactive thyroid are often like those of other conditions. They usually develop slowly, so you may not notice them for years.

Talk to your GP and ask to be tested for an underactive thyroid if you have symptoms including:

  • tiredness
  • weight gain
  • depression
  • feeling the cold more than usual
  • dry skin and hair
  • muscle aches

The only accurate way of finding out if you have a thyroid problem is to have a thyroid function test.  This is where a sample of blood is tested to measure your hormone levels.

Find out more about the symptoms of an underactive thyroid

Who's affected

Both men and women can have an underactive thyroid, but it's more common in women. Children can also develop an underactive thyroid and some babies are born with it.

Babies in Ireland have a heel prick test between 3 and 5 days old that screens for congenital hypothyroidism.

Treating an underactive thyroid

Treatment for an underactive thyroid involves taking daily hormone replacement tablets.

Levothyroxine tablets raise your thyroxine levels.

You'll have regular blood tests until the correct dose of levothyroxine is reached. This can take a little while to get right. When you're taking the correct dose, you'll have a blood test once a year to check your hormone levels.

You'll usually need treatment for the rest of your life. But with proper treatment, you can lead a normal, healthy life.

If an underactive thyroid is not treated, it can lead to complications.

These can include:

  • heart disease
  • goitre (an enlarged thyroid gland)
  • pregnancy problems 
  • myxoedema coma (a very rare but life-threatening condition)

Find out more about treatment for an underactive thyroid gland

The thyroid gland

The thyroid gland is a small butterfly-shaped gland in the neck, just in front of the windpipe (trachea).

One of its main functions is to produce hormones that help regulate the body's metabolism. These hormones are called triiodothyronine (T3) and thyroxine (T4).

Many of the body's functions slow down when the thyroid does not produce enough of these hormones.

Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 25 March 2021
Next review due: 25 March 2024