A guide to underactive and overactive thyroids

A guide to underactive and overactive thyroids

A guide to underactive and overactive thyroids

The thyroid is a butterfly-shaped gland in your neck. Although small in size, it plays a big role in keeping your body functioning as it should. It is responsible for producing hormones that regulate the body’s metabolic rate, brain development, digestion, bone maintenance and more. Problems can occur, however, if your body produces too much or too little of these hormones.

In this guide, we explore the two conditions that commonly affect the thyroid – hyperthyroidism and hypothyroidism.

Overactive thyroid (hyperthyroidism)

Whether you have been diagnosed with an overactive thyroid (also known as hyperthyroidism) or you think you may have this condition, you may be wondering exactly what having an overactive thyroid means, what causes it and how it can be treated. Read on to find out all this and more.

What is an overactive thyroid?

If you have an overactive thyroid it means that your thyroid produces too much of one or both of the thyroid hormones, triiodothyronine (T3) and thyroxine (T4).

Symptoms of an overactive thyroid can be wide ranging but may include:

  • hyperactivity
  • mood swings/aggression
  • nervousness, anxiety or irritability
  • tiredness
  • palpitations/rapid heartbeat
  • shakiness/trembling/tremors
  • unexplained weight loss
  • trouble sleeping
  • heat intolerance
  • sweating
  • thirst
  • swelling in the neck caused by enlarged thyroid gland (goitre)
  • neck pain
  • loose bowel movements
  • nausea

Hyperthyroidism is diagnosed using a blood test that measures your levels of triiodothyronine (T3), thyroxine (T4) and thyroid-stimulating hormone (TSH). You may need further blood tests or scans to determine the cause of your hyperthyroidism[1].

What causes an overactive thyroid?

Your thyroid can become overactive for a number of different reasons, including:

  • Graves’ disease

About 80 per cent of people with hyperthyroidism have Graves’ disease – an autoimmune disorder that most commonly affects young or middle aged women.

  • Thyroid nodules (or lumps)

Extra thyroid tissue can stimulate the production of excess thyroid hormones. Thyroid nodules or lumps are usually non-cancerous and are most commonly found in people over the age of 60.

  • Medicine containing iodine

If you are taking a medicine or vitamin supplement containing iodine, your thyroid gland may produce too much of the thyroid hormones. Amiodarone, which is used to manage arrhythmia, is an example of a medication that contains iodine.

  • Pregnancy

Human chorionic gonadotropin (HCG) is a hormone that is produced during pregnancy. High levels of HCG can cause hyperthyroidism. This may occur in early pregnancy, a molar pregnancy or if you become pregnant with multiples.

  • Thyroiditis

This refers to inflammation of the thyroid. Swelling can stimulate the production of additional thyroid hormones.

  • A pituitary adenoma

This refers to a benign tumour in the pituitary gland. A tumour in this area of the brain can cause more thyroid hormones to be produced.

  • Thyroid cancer

A cancerous thyroid tumour can cause an overactive thyroid. However, this is rare[2].

Is an overactive thyroid an autoimmune disease?

An overactive thyroid isn’t an autoimmune disease in and of itself. However, as discussed above, it can be caused by an autoimmune disease known as Graves’ disease. With this condition, your immune system attacks the thyroid, causing it to make excessive quantities of thyroid hormones. This disease affects more women than men and is the leading cause of hyperthyroidism[1].

How to treat an overactive thyroid

Fortunately, a variety of treatments exist for hyperthyroidism The main ones are:

  • Medicine

Anti-thyroid drugs known as thioamides can stop the overproduction of thyroid hormones. Your doctor may prescribe a thioamide called carbimazole or propylthiouracil. Once you start treatment, it can take a month or two to feel the benefits. You may be advised to gradually wean off this medicine once your hormone levels are under control. However, some people may need to take these tablets on a long-term basis.

  • Radioactive iodine treatment

This is a type of internal radiotherapy that can be used to lower the production of thyroid hormones by killing cells in the thyroid gland. The treatment involves taking a drink or capsule containing radioactive iodine, which targets your thyroid cells. Most of the time, people only require one round of treatment to cure their hyperthyroidism. Although the dose of radiation used during this therapy is very low, it is not suitable if you are pregnant, breastfeeding, planning to get pregnant in the next six months or planning to father a child in the next four months. It is also not appropriate if your overactive thyroid is causing eye problems. Patients also advised to avoid prolonged close contact with children and pregnant women for up to a few weeks after treatment.

  • Surgery

Sometimes, surgery is required to remove some or all of the thyroid gland. This may be a suitable treatment option if:

  • you have a severely swollen thyroid gland due to a goitre
  • your hyperthyroidism has resulted in severe eye problems
  • you are unable to have other treatments
  • your symptoms persist even after trying other treatments

Once your thyroid, or part of it, has been removed, your symptoms should not return. However, you will need to take a medicine called levothyroxine for the rest of your life. Levothyroxine is also used to treat an underactive thyroid, and helps to counter the effects of your thyroid hormones production levels not being as high as they should[1].

You may be able to alleviate some of the symptoms of hyperthyroidism by using self-help techniques, such as avoiding eating iodine-rich foods and using throat sprays to relieve throat pain. However, it should be noted that these techniques are not designed to treat hyperthyroidism itself.

Underactive thyroid (hypothyroidism)

About two per cent of the British population is affected by hypothyroidism (the name for having an underactive thyroid)[3]. If you are one of these people or you think you might be, you can find information about this condition, including what causes it and what treats it, below.

What is an underactive thyroid?

An underactive thyroid (or hypothyroidism) is one that does not produce enough of the thyroid hormone thyroxine (T4).

Hypothyroidism causes symptoms that can also be associated with a number of other health conditions so it can be difficult to identify the problem. Symptoms also often develop slowly over a number of years so it is not uncommon to receive a diagnosis after experiencing symptoms for a long time[3].

Symptoms include:

  • tiredness and fatigue
  • sensitivity to the cold
  • dry and coarse skin
  • dry and thinning hair
  • memory problems
  • trouble concentrating
  • weight gain
  • constipation
  • muscle weakness, aches and cramps
  • low mood or depression
  • sow thoughts and movements
  • fertility problems
  • low libido
  • heavy or irregular periods
  • numbness or tingling in fingers and hands (carpal tunnel syndrome)

If left untreated, you may also experience:

  • a slow heartbeat
  • anaemia
  • a hoarse voice
  • loss of hearing
  • facial puffiness
  • thinned eyebrows

An underactive thyroid is diagnosed using a blood test called a thyroid function test, which measures the levels of thyroxine (T4) and thyroid-stimulating hormone (TSH) in your blood.

What causes an underactive thyroid?

Your thyroid may not produce sufficient quantities of thyroxine for a number of reasons[3]. Here are some of the causes:

  • Autoimmune thyroid disease

This occurs when your immune system attacks the thyroid cells. This is the most common cause of an underactive thyroid gland. Hashimoto’s thyroiditis is the most prevalent form of this disease.

  • Previous thyroid treatment

If you have undergone surgery or radioactive iodine treatment to treat hyperthyroidism or thyroid cancer, you may experience hypothyroidism as a side effect or complication.

  • Anti-thyroid medicines

If you are prescribed too high a dose of anti-thyroid drugs to treat hyperthyroidism, you may experience an underactive thyroid as a result.

  • Lack of dietary iodine

You need iodine to produce thyroxine so insufficient iodine levels can result in an underactive thyroid. However, this is an uncommon cause in the UK.

  • Congenital hypothyroidism

This happens when a baby is born with hypothyroidism because their thyroid gland does not develop properly in utero. It is uncommon and is normally identified during routine screening tests after birth.

  • Certain medicines

Lithium, which is used to treat some mental health conditions, interferons, which are used to treat hepatitis C and some cancers, and amiodarone, which is used to control specific heart problems, are associated with an increased risk of hypothyroidism.

  • Viral infections

Viral infections have been linked to the development of an underactive thyroid in some cases.

Is an underactive thyroid an autoimmune disease?

While an underactive thyroid is not classified as an autoimmune disease, autoimmune disease is a major cause of hypothyroidism. As discussed above, Hashimoto’s disease is the autoimmune disease most commonly associated with an underactive thyroid gland. This disease runs in families and is common in those who also have another autoimmune disorder[3].

How to treat an underactive thyroid

An underactive thyroid can usually be treated effectively by taking a hormone replacement tablet called levothyroxine on a daily basis. It’s important to take this tablet on an empty stomach at the same time each day. At first, regular blood tests will be required to determine the right dose of levothyroxine for you.

Some people notice the benefits of levothyroxine soon after treatment commences. However, it may take several months for some people to feel improvements. Once you’ve found the right dose for you, you’ll have annual blood tests to check that your condition is still under control. If you are pregnant, your levels should be monitored regularly and you may require a higher dose of levothyroxine.

You will not experience side effects unless you’re taking too much levothyroxine[3]. Signs that you’re taking too much levothyroxine include chest pains, sweating, headaches, vomiting and diarrhoea. If you think you may have a problem with your thyroid, you should consult your doctor. This information should not be used as a substitute for medical advice.


[1] https://www.nhs.uk/conditions/overactive-thyroid-hyperthyroidism/

[2] https://www.nhs.uk/conditions/thyroid-cancer/

[3] https://www.nhs.uk/conditions/underactive-thyroid-hypothyroidism/