Hyperthyroidism (overactive thyroid)

Hyperthyroidism, also known as overactive thyroid gland, is a condition brought on when the thyroid gland produces too much thyroid hormone. When the thyroid gland is overactive it causes too much of a hormone called thyroxine to be released, which causes many of the processes in the body to be sped up. Thyroxine plays a role in the regulation of metabolism and is essential for many of the cells and tissues in the body to work effectively.

Hyperthyroidism may sometimes be called thyrotoxicosis by doctors. Hyperthyroidism is fairly common and tends to affect women more commonly than men. It is estimated that 1 in 100 women and 1 in 1,000 men will suffer from hyperthyroidism at some point in their lives.

Hyperthyroidism is the opposite of hypothyroidism, which causes the thyroid gland to be underactive.

What causes hyperthyroidism?

There are numerous different causes of hyperthyroidism with the most common being Graves’ disease.

Graves’ disease

Graves’ disease is an autoimmune disease, which most commonly affects women aged between 20 and 40. Graves’ disease can affect anyone but it is common for there to be a family history. Autoimmune diseases cause the body to make antibodies that fight healthy tissue or organs, as they are mistaken for a harmful threat. In the case of Graves’ disease the antibodies become attached to the thyroid gland, causing the gland to generate too much thyroxine. In most cases of Graves’ disease the thyroid gland becomes swollen, with around half of the people with Graves’ disease suffering from problems related to their eyes. Graves’ disease can cause the eyes to be pushed forward, making them appear more prominent in the face (this is known as proptosis) and causing watery and sore eyes.


Nodules on the thyroid gland can also cause hyperthyroidism, although this is much less common than Graves’ disease. Thyroid nodules are small bumps which develop on the thyroid gland. They are not usually cancerous but do contain abnormal thyroid cells, which do not respond in the normal way and cause too much thyroxine to be produced. There is potential for a single nodule to develop (this is called a toxic solitary adenoma), which is most frequently found in people aged between 30 and 50. In older people it is common for the thyroid gland to become lumpy, which is known as a toxic multinodular goitre.

Rare causes of hyperthyroidism

There are other possible causes of hyperthyroidism buy they are rare. These include:

  • Taking medication including lithium and amiodarone.
  • Taking iodine supplements.
  • Follicular thyroid cancer.

Symptoms of hyperthyroidism

Symptoms of hyperthyroidism tend to develop gradually over a number of weeks. They include:

  • Increased appetite.
  • Weight loss.
  • Shaky hands.
  • Sweating.
  • Feeling thirsty.
  • Being restless, anxious and irritable.
  • Palpitations.
  • Eye problems (if hyperthyroidism is caused by Graves’ disease).
  • Tiredness.
  • Muscle weakness.
  • Thinning hair.
  • Swelling of the thyroid gland.

Most people do not suffer from all of the symptoms listed above, but it is common for people to experience at least two of the symptoms. Symptoms are usually mild initially and then get gradually worse as the level of thyroxine in the blood increases.

Complications of hyperthyroidism

If hyperthyroidism is left untreated it can contribute to complications, including:

  • Increased risk of heart problems, such as angina, atrial fibrillation (an irregular heart rhythm), heart failure and cardiomyopathy (weakening of the heart muscle).
  • Increased risk of complications during pregnancy.
  • Increased risk of developing osteoporosis, a condition that causes the bones to become weaker.

How is hyperthyroidism diagnosed?

If you notice any signs or generally don’t feel well you should arrange to see your GP. They will want to learn about any symptoms you have noticed, your past medicinal history and there is the chance they will perform an examination. Hyperthyroidism can be diagnosed through blood tests. Blood samples are checked for elevated levels of thyroxine (T4) and thyroid stimulating hormone (TSH), which is made by the pituitary gland and released into the bloodstream to stimulate the thyroid gland in its production of thyroxine. If there is too much thyroxine in the blood the pituitary gland releases lower levels of TSH, so if the blood test results show a low level of TSH and a high level of T4 this indicates hyperthyroidism.

If the test results are ambiguous the tests may be repeated to ensure an accurate diagnosis. If a rare cause of the condition is suspected additional tests may be carried out.

Treatment for hyperthyroidism

There is a variety of treatment options for hyperthyroidism, the aims of which are to lessen the amount of thyroxine in the blood and treat symptoms. Your doctor will decide the best course of treatment based on your age, medical history, the underlying cause of hyperthyroidism and the mass of the goitre (the swelling of the thyroid gland). Treatment options include:


Medication can be used to reduce the amount of thyroxine produced by the thyroid gland. The most commonly used form of medication is carbimazole. This drug reduces further production of thyroxine but does not affect hormones that have already been produced, which means that it can take up to eight weeks to work. The dose of carbimazole varies according to the individual, but in most cases the dose starts high and comes down over time as thyroxine levels decrease. Carbimazole is usually prescribed for between 12 and 18 months initially; however, if the condition flares up again another course may be required. In rare cases carbimazole can affect the white blood cells, so it is imperative that you choose to visit your GP if you notice signs of an infection, including high temperature, sore throat or mouth ulcers.

A drug called propylthiouracil is often used as an alternative to carbimazole for women who are pregnant or breastfeeding.


This treatment involves drinking a liquid or taking a capsule that contains radioactive iodine. Usually iodine is used to produce thyroxine, so that the radioactive iodine collects in the thyroid gland destroying some of the thyroid tissue and reducing the amount of thyroxine produced by the thyroid gland. The dose is very low and will not damage any other cells or tissues in the body. This treatment is not suitable for pregnant women or women who are breastfeeding. Patients treated with radioactive iodine are advised to avoid close physical contact with babies, children and pregnant women. You may also have to sleep alone and stay away from pets for a period of at least 2 weeks after treatment, to decrease the radiation exposure for other people and family pets.


If the thyroid gland is very swollen (there is a large goitre) surgery may be an option, which involves removing part or all of the thyroid gland. If the entire thyroid gland is removed patients are given hormone replacement tablets.

Thyroid replacement therapy

If medication is prescribed for patients with hyperthyroidism, regular tests will be carried out to check the levels of thyroxine. If the levels are too high or too low the dose of medication will be altered. It is possible to use a technique called block and replace, which involves taking a high daily dose of carbimazole or a one-off high dose of radioiodine to stop thyroxine production. This is supplemented by thyroxine tablets to keep the levels of thyroxine in the blood stable.


Beta-blockers may be prescribed to help ease symptoms such as nervousness, tremors, sweating and agitation.

Eye treatment

Some people with Graves’ disease develop problems with their eyes and in such cases the patient will be referred to an eye specialist. Minor symptoms can usually be treated by using artificial tears, wearing sunglasses and using eye protectors during sleep. More severe symptoms may require more intensive treatment including surgery, steroid medication and radiation treatment.

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