Underactive thyroid

Underactive thyroid

Introduction

Symptoms of an underactive thyroid

Many symptoms of an underactive thyroid (hypothyroidism) are the same as those of other conditions, so it can easily be confused for something else.

Symptoms usually develop slowly and you may not realise you have a medical problem for several years.

Common symptoms include:

Elderly people with an underactive thyroid may develop memory problems and depression. Children may experience slower growth and development. Teenagers may start puberty earlier than normal.

If you have any of these symptoms, see your GP and ask to be tested for an underactive thyroid.

Read more about getting tested for an underactive thyroid.

If an underactive thyroid isn’t treated

It’s unlikely that you’d have many of the later symptoms of an underactive thyroid, because the condition is often identified before more serious symptoms appear.

Later symptoms of an underactive thyroid include:

  • a low-pitched and hoarse voice
  • a puffy-looking face
  • thinned or partly missing eyebrows
  • a slow heart rate
  • hearing loss
  • anaemia

Causes of underactive thyroid

Diagnosing underactive thyroid

It’s very important that an underactive thyroid (hypothyroidism) is diagnosed as soon as possible.

Low levels of thyroid-producing hormones, such as triiodothyronine (T3) and thyroxine (T4), can change the way the body processes fat.

This can cause high cholesterol and atherosclerosis (clogging of the arteries), which can potentially lead to serious heart-related problems, such as angina and heart attack.

Therefore, you should see your GP and ask for a blood test if you repeatedly have symptoms of an underactive thyroid.

Thyroid function test

A blood test measuring your hormone levels is the only accurate way to find out whether there’s a problem.

The test, called a thyroid function test, looks at levels of thyroid-stimulating hormone (TSH) and thyroxine (T4) in the blood.

A high level of TSH and a low level of T4 in the blood could mean you have an underactive thyroid.

If your test results show raised TSH but normal T4, you may be at risk of developing an underactive thyroid in the future.

Your GP may recommend that you have a repeat blood test every so often to see whether you eventually develop an underactive thyroid.

Blood tests are also sometimes used for other measurements, such as checking the level of a hormone called triiodothyronine (T3). However, this isn’t routine, because T3 levels can often remain normal, even if you have a significantly underactive thyroid.

The Lab Tests Online UK website has more information about the different types of thyroid function tests.

Referral

Your GP may refer you to an endocrinologist (a specialist in hormone disorders) if you:

  • are younger than 16
  • are pregnant or trying to get pregnant
  • have just given birth
  • have another health condition, such as heart disease, which may complicate your medication
  • are taking a medication known to cause a reduction in thyroid hormones, such as amiodarone or lithium

Treating underactive thyroid

An underactive thyroid (hypothyroidism) is usually treated by taking daily hormone replacement tablets called levothyroxine.

Levothyroxine replaces the thyroxine hormone, which your thyroid doesn’t make enough of.

You’ll initially have regular blood tests until the correct dose of levothyroxine is reached. This can take a little while to get right.

You may start on a low dose of levothyroxine, which may be increased gradually, depending on how your body responds. Some people start to feel better soon after beginning treatment, while others don’t notice an improvement in their symptoms for several months

Once you’re taking the correct dose, you’ll usually have a blood test once a year to monitor your hormone levels.

If blood tests suggest you may have an underactive thyroid, but you don’t have any symptoms or they’re very mild, you may not need any treatment. In these cases, your GP will usually monitor your hormone levels every few months and prescribe levothyroxine if you develop symptoms.

Taking levothyroxine

If you’re prescribed levothyroxine, you should take one tablet at the same time every day. It’s usually recommended that you take the tablets in the morning, although some people prefer to take them at night.

The effectiveness of the tablets can be altered by other medications, supplements or foods, so they should be swallowed with water on an empty stomach, and you should avoid eating for 30 minutes afterwards.

If you forget to take a dose, take it as soon as you remember, if this is within a few hours of your usual time. If you don’t remember until later than this, skip the dose and take the next dose at the usual time, unless advised otherwise by your doctor.

An underactive thyroid is a lifelong condition, so you’ll usually need to take levothyroxine for the rest of your life.

If you’re prescribed levothyroxine because you have an underactive thyroid, you’re entitled to a medical exemption certificate. This means you don’t have to pay for your prescriptions. See getting help with prescription costs for more information on this.

Side effects

Levothyroxine doesn’t usually have any side effects, because the tablets simply replace a missing hormone.

Side effects usually only occur if you’re taking too much levothyroxine. This can cause problems including sweating, chest pain, headaches, diarrhoea and vomiting.

Tell your doctor if you develop new symptoms while taking levothyroxine. You should also let them know if your symptoms get worse or don’t improve.

Triiodothyronine (T3) treatment

In the UK, treatment for an underactive thyroid involving a combination of levothyroxine and a hormone called triiodothyronine (T3) isn’t usually recommended, because studies have found no evidence this is more effective.

There are also concerns that taking both these hormone replacement medications may increase your risk of serious side effects, such as an irregular heartbeat (arrhythmia) and weak bones (osteoporosis).

Complications of underactive thyroid

Several complications can occur if you have an underactive thyroid that isn’t treated.

Heart problems

If you have an untreated underactive thyroid, your risk of developing cardiovascular disease is increased.

This is because having low levels of the hormone thyroxine can lead to increased levels of cholesterol in your blood. High cholesterol can cause fatty deposits to build up in your arteries, restricting the flow of blood.

Contact your doctor if you’re being treated for an underactive thyroid and you develop chest pain, so that any problems can be detected and treated, if necessary. 

Goitre

goitre is an abnormal swelling of the thyroid gland that causes a lump to form in the throat. Goitres can develop in people with an underactive thyroid when the body tries to stimulate the thyroid to produce more thyroid hormones.

Pregnancy complications

If an underactive thyroid isn’t treated during pregnancy, there’s a risk of problems occurring. These include:

These problems can usually be avoided with treatment under the guidance of a specialist in hormone disorders (an endocrinologist). Therefore, tell your GP if you have an underactive thyroid and you’re pregnant or trying to get pregnant.

Myxoedema coma

In very rare cases, a severe underactive thyroid may lead to a life-threatening condition called myxoedema coma. This is where the thyroid hormone levels become very low, causing symptoms such as confusion, hypothermia and drowsiness.

Myxoedema coma requires emergency treatment in hospital. It’s usually treated with thyroid hormone replacement medication given directly into a vein. In some cases, other treatments such as breathing support, antibiotics and steroid medication (corticosteroids) are also required.