Overactive thyroid

Also known as hyperthyroidism

An overactive thyroid (hyperthyroidism) is when your thyroid gland makes too many thyroid hormones.

Key points about overactive thyroid

  1. An overactive thyroid can cause weight loss, anxiety, rapid heartbeat, sleep problems and low energy.
  2. Common causes include Graves’ disease, thyroid nodules, thyroiditis and certain medicines such as amiodarone.
  3. If you have symptoms of an overactive thyroid, see your doctor for a diagnosis.
  4. Possible treatments include medicines, radioactive iodine or surgery.
  5. If an overactive thyroid is left untreated, you will develop heart problems, eye problems, osteoporosis or a life-threatening condition called thyroid storm.

See your GP, go to the nearest emergency department or call 111 for an ambulance if you or someone you care for has thyroid disease and experiences any of the following:

  • a very high temperature or fever
  • very fast heart rate or palpitations
  • shortness of breath
  • confusion
  • agitation
  • delirium or psychosis
  • nausea (feeling sick) or vomiting (being sick)
  • fainting or loss of consciousness
  • feeling very unwell.

You may have a condition known as thyroid storm, hyperthyroid crisis or thyrotoxic crisis, which is a medical emergency. You have high or very high levels of thyroid hormones and need immediate treatment.

What is the thyroid gland?

undefinedYour thyroid is a small, butterfly-shaped gland in your neck. It produces 2 thyroid hormones: tri-iodothyronine (T3) and thyroxine (T4). Thyroid hormones help your body use energy, stay warm and keep your brain, heart, muscles and other organs working as they should.

What causes an overactive thyroid?

Thyroid problems can affect anyone, but are more common in women than men.

An overactive thyroid can be caused by a number of conditions:

  • Graves’ disease – this is the most common cause. It is an autoimmune disease in which your body’s immune system mistakenly attacks your thyroid gland. It can be passed on in families (hereditary).
  • Thyroid nodules or lumps. These are benign or non-cancerous tumours that grow on your thyroid. These nodules can produce extra thyroid hormones. Read more about thyroid nodules.
  • Too much iodine in your body. This can be caused by taking iodine supplements such as kelp or seaweed
  • Thyroiditis or inflammation of your thyroid gland, possibly caused by a virus or problem with your immune system.
  • Some medicines such as lithium or amiodarone can cause an overactive thyroid.
  • Thyroid cancer. This is rare, but a thyroid cancer can affect the production of thyroid hormones by your thyroid gland.

What are the symptoms of an overactive thyroid?

People with an overactive thyroid may have no symptoms at all, or symptoms may start off mild and then progressively get worse.

These may include:

  • losing weight, even though eating the same amount or more than usual
  • feeling nervous, anxious, moody, weak or tired
  • shaky hands or a tremor in them
  • fast heart beat or palpitations
  • problems breathing
  • feeling hot and sweaty or warm, red, itchy skin
  • having looser, more frequent, bowel movements (poo) than usual
  • losing hair, especially fine, soft hair
  • trouble sleeping
  • a swollen thyroid gland, also known as goitre
  • problems with your eyes or vision – this is more common if you have Graves’ disease
  • lighter or no menstrual periods.

How are the causes of an overactive thyroid diagnosed?

The diagnosis of hyperthyroidism may not be obvious at first because symptoms may be mild. If you have symptoms described above, see your doctor for a diagnosis. Your doctor will ask you questions about your symptoms, including whether you are taking any medicines that may cause a high level of thyroid hormones in your body. Your doctor will also examine you and check your thyroid gland.

Some tests your doctor may carry out to help diagnose the cause of an overactive thyroid include:

  • a thyroid function test – this is a blood test that measures your thyroid hormones (T3, T4) and thyroid stimulating hormone (TSH)
  • a blood test to test for TSH receptor antibody – if you have Graves’ disease, this antibody level can be high.

Depending on your blood tests results, a nuclear scan of your thyroid may or may not be done. A nuclear scan can find out whether your thyroid has any nodules and examine the size and shape of your thyroid. You may be referred to an endocrinologist (a doctor who specialises in hormones) for further testing if the cause is still unknown.


How is an overactive thyroid treated?

Treatment depends on the cause of your overactive thyroid, your age, the severity of your condition, other medical conditions that may be affecting your health and your own preference. Your doctor will discuss the best treatment option with you.

The possible treatments for overactive thyroid are medicines, radioactive iodine therapy and surgery:


  • Beta-blockers such as propranolol or metoprolol medicines help your symptoms by blocking the effects of thyroid hormones on your body such as shaking, tremor, anxiety or fast heartbeat. These medicines are given for a short time and can help you feel better while you and your doctor decide what your treatment should be.
  • Antithyroid medicines such as carbimazole work by blocking your thyroid gland from producing thyroid hormones.

Radioactive iodine therapy

  • This involves taking a drink or swallowing a capsule that contains radioactive iodine.
  • This damages the cells in your thyroid gland that produce thyroid hormones.
  • Radioactive iodine is very safe and effective, but you will need follow-up blood tests, as the main side effect of this treatment is an underactive thyroid (hypothyroidism).


  • This involves an operation in which all or part of your thyroid gland is removed.
  • This is often the last resort and is a consideration if all other therapies and medicines have not worked.
  • Surgery is a good option if you have a large tumour (goitre) that is causing problems with your neck.
  • After you have received treatment, you will need follow-up blood tests to monitor your thyroid hormone levels.

Read more about the treatment of hyperactive thyroid.

What are the possible complications of an overactive thyroid?

If hyperthyroidism goes untreated for a long time, it may lead to severe complications, which can be avoided with treatment.

These include:

  • heart problems such as atrial fibrillation or heart failure
  • eye problems
  • brittle bones or osteoporosis
  • a thyroid storm (fever, delirium, rapid pulse or loss of consciousness) – this is an medical emergency that needs immediate treatment.

What support is available with overactive thyroid?

The NZ Thyroid Support Group provides support for people to meet, talk and share information about thyroid disorders. Visit their website or contact them by phone: 09 480 2680.

Learn more

The following links provide further information about overactive thyroid. Be aware that websites from other countries may have information that differs from New Zealand recommendations.   

Overactive thyroid (hyperthyroidism) HealthInfo Canterbury, NZ
Hyperthyroidism DermNet NZ
Thyroid – hyperthyroidism Better Health Channel, Australia
Hyperthyroidism, Graves’ disease & thyroid eye disease The Australian Thyroid Foundation, Australia
Overactive thyroid gland Patient Info, UK
Overactive thyroid NHS, UK 


  1. Hyperthyroidism 3D Regional HealthPathways, NZ, 2021
  2. Campbell K, Doogue M. Evaluating and managing patients with thyrotoxicosis Australian Family Physician. 2012. 41(8):564-572.
  3. Management of thyroid dysfunction in adults BPAC, NZ, 2010
  4. Hyperthyroidism Patient Info, UK
Credits: Health Navigator Editorial Team.