Warning notification:Warning

Unfortunately, you are using an outdated browser. Please, upgrade your browser to improve your experience with HSE. The list of supported browsers:

  1. Chrome
  2. Edge
  3. FireFox
  4. Opera
  5. Safari

Overview - Overactive thyroid (hyperthyroidism)

An overactive thyroid produces too much thyroid hormone. The condition is also known as hyperthyroidism or thyrotoxicosis. 

The thyroid is a small butterfly-shaped gland in the neck, just in front of the windpipe (trachea). It produces hormones that affect things such as your heart rate and body temperature.

Having too much of these hormones can cause serious problems that may need treatment.

An overactive thyroid can affect anyone. It's about 10 times more common in women than men. It usually happens between 20 and 40 years of age.

Symptoms of an overactive thyroid

An overactive thyroid can cause a wide range of symptoms, including:

  • nervousness, anxiety and irritability
  • mood swings
  • difficulty sleeping
  • persistent tiredness and weakness
  • sensitivity to heat
  • swelling in your neck from an enlarged thyroid gland (goitre)
  • an irregular or unusually fast heart rate (palpitations)
  • twitching or trembling
  • weight loss

Symptoms of an overactive thyroid

When to see your GP

See your GP if you have symptoms of an overactive thyroid.

They'll ask about your symptoms. They can arrange for a blood test to check how well your thyroid is working.

If you have an overactive thyroid, you may be sent for more tests to find out the cause.

How an overactive thyroid is diagnosed

Causes of an overactive thyroid

There are several reasons why your thyroid can become overactive.

Graves' disease

This is a condition where your immune system mistakenly attacks and damages the thyroid. About 3 in every 4 people with an overactive thyroid have Graves' disease.

Lumps (nodules) on the thyroid

Extra thyroid tissue can produce thyroid hormones, causing your levels to be too high.


Some medicines may cause your thyroid to become overactive. For example, amiodarone, which can be used to treat an irregular heartbeat (arrhythmia).

Causes of an overactive thyroid

Treatments for an overactive thyroid

An overactive thyroid is usually treatable.

The main treatments are:

  • medicine that stops your thyroid producing too much of the thyroid hormones
  • radioiodine treatment – where a type of radiotherapy is used to destroy cells in the thyroid, reducing its ability to produce thyroid hormones
  • surgery to remove some or all of your thyroid, so that it no longer produces thyroid hormones

Each of these treatments has benefits and drawbacks. A specialist in hormonal conditions (endocrinologist) will discuss which treatment is best for you.

Treatment for an overactive thyroid

Further problems

An overactive thyroid can sometimes lead to further problems.

These include:

  • eye problems - such as eye irritation, double vision or bulging eyes
  • pregnancy complications - such as pre-eclampsia, premature birth or miscarriage
  • a thyroid storm - a sudden and life-threatening flare-up of symptoms

Complications of an overactive thyroid

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

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

Page last reviewed: 14 March 2021
Next review due: 14 March 2024