Overactive thyroid

Also known as hyperthyroidism or thyrotoxicosis

An overactive thyroid (hyperthyroidism) is when your thyroid gland makes too much thyroid hormone.

On this page, you can find the following information:

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, radioiodine or surgery.
  5. If an overactive thyroid is not treated, you could 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 or hallucinations
  • agitation
  • nausea (feeling sick) or vomiting (being sick)
  • fainting or loss of consciousness
  • feeling very unwell.

These symptoms could be a sign of very high thyroid hormone levels (known as thyroid storm, hyperthyroid crisis or thyrotoxic crisis). It is a medical emergency and needs 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. Sometimes this condition runs in families.
  • Thyroid nodules. These are benign (non-cancerous) lumps that grow on your thyroid. They 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 (inflammation of your thyroid gland). This can be caused by a virus or can happen soon after having a baby. 
  • 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.

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 gradually get worse.

Symptoms may include:

  • losing weight, even though you are eating the same amount or more than usual
  • feeling nervous, anxious, moody, weak or tired
  • tremor (shaky hands)
  • palpitations (fast or ‘thumping’ heartbeat)
  • problems breathing
  • feeling hot and sweaty
  • having looser, more frequent, bowel movements (poo) than usual
  • skin problems such as a rash, itching or hair thinning
  • 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. See your doctor if you have any of the symptoms noted above. Your doctor will ask you questions, including whether you are taking any medicines or supplements that may affect your thyroid gland. Your doctor will usually do a physical examination and arrange blood tests which may include:

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

If blood tests show you have an overactive thyroid, you will be referred to an endocrinologist (a specialist hormone doctor).  Sometimes other tests are needed, such as a scan of your thyroid gland.


Image: 123RF

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, radioiodine therapy and surgery:


  • Beta blockers such as propranolol or metoprolol medicines reduce symptoms such as shaking, anxiety or fast heartbeat by blocking the effects of thyroid hormones on your body. These medicines are given for a short time to 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.

Radioiodine therapy

  • Radioiodine works by destroying overactive thyroid cells.
  • Treatment involves taking a drink or swallowing a capsule that contains radioactive iodine.
  • Radioiodine is one of the safest treatments available for an overactive thyroid.
  • Read about radioactive iodine therapy here.


  • This involves an operation in which all or part of your thyroid gland is removed.
  • Surgery is considered an option if other therapies and medicines have not worked.
  • Surgery is also 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
  • osteoporosis (brittle bones)
  • 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 and 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

Reviewed by

Dr Alice Miller trained as a GP in the UK and has been working in New Zealand since 2013. She has undertaken extra study in diabetes, sexual and reproductive healthcare, and skin cancer medicine. Alice has a special interest in preventative health and self-care, which she is building on by studying for the Diploma of Public Health with the University of Otago in Wellington.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Alice Miller, GP, FRNZCGP, Wellington Last reviewed: 27 Sep 2021