Overactive thyroid (hyperthyroidism)

Overactive thyroid means your thyroid gland is releasing too much thyroid hormone. This speeds up your body's metabolism, leading to symptoms such as shaking, weight loss and anxiety.

About overactive thyroid

If you have overactive thyroid it means your thyroid gland is producing too much thyroid hormone.

Your thyroid gland is in your neck, in front of your windpipe. It releases two hormones to control how quickly your body uses its energy stores and how sensitive your body is to other hormones.

Image showing the location of the thyroid gland and surrounding structures.

In the UK, about one in 100 people have overactive thyroid and it’s about six times more common in women than in men.

Symptoms of overactive thyroid

Symptoms of overactive thyroid can include:

  • feeling nervous, irritable or hyperactive
  • having tremors (shaking)
  • being unable to cope with heat
  • sweating more than usual
  • losing weight, despite having an increased appetite
  • feeling tired
  • muscle weakness
  • having an increased heart rate (palpitations)
  • irregular menstrual periods, if you’re a woman
  • having more frequent bowel movements or diarrhoea
  • shortness of breath, especially when exercising
  • thinning or loss of hair
  • an enlarged thyroid gland (goitre), which causes a lump to develop in your throat
  • abnormal breast growth in men (gynaecomastia)

These symptoms aren’t always caused by overactive thyroid but if you have them, see your GP.

Complications of overactive thyroid

If left untreated, overactive thyroid can increase your risk of heart failure and you may develop problems with your vision. Rarely, you may develop a life-threatening reaction called a thyroid storm (thyrotoxic crisis). The symptoms of a thyroid storm include having a very fast heart beat, fever and jaundice (where your skin and the whites of your eyes appear yellow in colour).

If you’re a woman, having overactive thyroid can increase your risk of infertility, oligomenorrhoea (infrequent or very light menstrual periods) and amenorrhoea (the absence of menstrual periods). If you become pregnant, having overactive thyroid may increase your risk of having a miscarriage, premature birth or a baby with low birthweight.

Causes of overactive thyroid

The most common causes of overactive thyroid are described below.

  • Graves’ disease. This is an autoimmune disease. Your immune system produces antibodies (proteins produced by your immune system that usually fight against bacteria and viruses) that trigger your thyroid gland to produce thyroid hormones.
  • Nodular thyroid disease. Lumps or nodules develop in your thyroid gland and produce thyroid hormones.
  • Certain medicines (eg amiodarone). Iodine in medicines can trigger your thyroid gland to produce thyroid hormones.

Diagnosis of overactive thyroid

Your GP will ask about your symptoms and examine you. He or she may also ask you about your medical history. Your GP may take a blood sample to check your levels of thyroid hormones and to look for specific antibodies.

If blood tests confirm you have overactive thyroid, your GP will either advise you about your treatment options, or refer you to an endocrinologist (a doctor who specialises in identifying and treating conditions of the endocrine system).

You may also need to have a radioisotope scan. This involves having a small amount of a radioactive substance injected into your blood, which is taken up by your thyroid gland. Scans of your thyroid gland will show up any overactive areas.

Treatment of overactive thyroid

Treatment aims to return your levels of thyroid hormones to normal.


Your doctor may prescribe you anti-thyroid medicines such as carbimazole or propylthiouracil to suppress thyroid hormone production in your thyroid gland. You will need to take these medicines for 12 to 18 months. These medicines can lead to an underactive thyroid (hypothyroidism), so you will need regular blood tests to check your levels of thyroid hormones.

Your doctor may also prescribe you beta-blockers to help manage the symptoms of overactive thyroid until your hormone levels return to normal. These don't, however, treat the underlying problem.

Non-surgical treatments

Your doctor may suggest having radioiodine treatment. This involves taking iodine as a tablet or drink, which is taken up by your thyroid gland. As the radioactivity builds up it destroys some of your thyroid tissue, so the gland produces less thyroid hormones. You may be given a single, large dose of radioiodine to stop all your thyroid activity. If radioiodine treatment successfully reduces the activity of your thyroid gland, you will need to take levothyroxine (thyroid hormone replacement medicine) every day for the rest of your life.

Radioiodine treatment isn’t suitable if you're a woman and you’re pregnant or breastfeeding.


Your doctor may suggest having an operation to remove all or part of your thyroid gland (called a thyroidectomy). Before surgery, your thyroid hormone levels will need to be controlled. This is because overactive thyroid can increase your risk of anaesthetic-related complications. After surgery, you may need to take levothyroxine every day for the rest of your life. If you need more information, speak to your doctor.


Produced by Krysta Munford, Bupa Health Information Team, May 2012.

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.

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  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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