Underactive thyroid
Underactive thyroid
About underactive thyroids
Symptoms of an underactive thyroid
Causes of an underactive thyroid
Diagnosing an underactive thyroid
Treating an underactive thyroid
Complications of an underactive thyroid
About underactive thyroids
An underactive thyroid, known medically as hypothyroidism, means your thyroid gland is not producing enough hormones for your body's needs.
Common signs include feeling unusually tired, gaining weight, and feeling low or depressed.
This condition can usually be managed well by taking a daily hormone tablet that replaces the hormones your thyroid is no longer making enough of.
There is no known way to prevent an underactive thyroid. Most cases happen either because the immune system attacks and damages the thyroid gland, or because the thyroid is damaged during treatment for an overactive thyroid or thyroid cancer.
You can read more about the causes of an underactive thyroid below.
Common Symptoms
⚠️ This symptom list is for educational purposes. Having these symptoms does not mean you have this condition. See a doctor for proper diagnosis.
Medicines Commonly Used
⚠️ These medicines are commonly used for confirmed diagnoses of this condition. This is NOT a recommendation or prescription. Treatment must be determined by your doctor.
No medicines have been linked to this condition yet.
When to See a Doctor
If you have an underactive thyroid, symptoms often look like signs of other conditions, and they usually build up slowly, so you might not notice them for years.
You should see your doctor and ask about testing for an underactive thyroid if you notice:
- tiredness
- weight gain
- low mood or depression
- feeling the cold more than usual
- dry skin and hair
- aching muscles
The only reliable way to know whether you have a thyroid problem is a thyroid function test, where a blood sample is checked to measure your hormone levels.
Who is affected
Both men and women can develop an underactive thyroid, though it is more common in women. In the UK, about 15 in every 1,000 women and 1 in every 1,000 men are affected. Children can develop it too.
Around 1 in every 3,500 to 4,000 babies is born with an underactive thyroid, known as congenital hypothyroidism. In the UK, every newborn is screened for this using a blood spot test at about 5 days old.
Causes
Causes of an underactive thyroid
An underactive thyroid (hypothyroidism) is when your thyroid gland doesn’t produce enough of the hormone thyroxine (also called T4).
Most cases of an underactive thyroid are caused by the immune system attacking the thyroid gland and damaging it, or by damage that occurs as a result of treatments for thyroid cancer or an overactive thyroid.
Immune system
An underactive thyroid often occurs when the immune system, which usually fights infection, attacks the thyroid gland. This damages the thyroid, which means it’s not able to make enough of the hormone thyroxine, leading to the symptoms of an underactive thyroid.
A condition called Hashimoto’s disease is the most common type of autoimmune reaction that causes an underactive thyroid.
It’s not clear what causes Hashimoto’s disease, but it runs in families. It’s also common in people with another immune system disorder, such as type 1 diabetes and vitiligo.
Less common causes
Worldwide, a lack of dietary iodine is a common cause of an underactive thyroid, because the body needs iodine to make thyroxine. However, iodine deficiency is uncommon in the UK.
Babies are sometimes born with an underactive thyroid because the thyroid gland doesn’t develop properly in the womb. This is called congenital hypothyroidism and is uncommon, affecting around 1 in 3,000 babies. It’s usually picked up during routine screening soon after birth.
A problem with the pituitary gland could lead to an underactive thyroid. The pituitary gland sits at the base of the brain and regulates the thyroid. Therefore, damage to the pituitary gland may lead to an underactive thyroid.
An underactive thyroid has also been linked to some viral infections or some medications used to treat other conditions, such as:
- lithium – a medication sometimes used to treat certain mental health conditions, including depression and bipolar disorder
- amiodarone – a medication sometimes used to treat irregular heartbeats (arrhythmias)
- interferons – a class of medication sometimes used to treat certain types of cancer and hepatitis C
Speak to your GP or specialist if you’re concerned that a medication you’re taking may be affecting your thyroid hormone levels.
Diagnosis
Diagnosing an 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
Taking levothyroxine
If you’re prescribed levothyroxine, you should take 1 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.
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.
Treatment
Treating an underactive thyroid
Treatment for an underactive thyroid involves taking daily hormone replacement tablets, called levothyroxine, to raise your thyroxine levels. You’ll usually need treatment for the rest of your life. However, with proper treatment, you should be able to lead a normal, healthy life.
If an underactive thyroid isn’t treated, it can lead to complications, including heart disease, goitre, pregnancy problems and a life-threatening condition called myxoedema coma (although this is very rare).
Read more about treating an underactive thyroid and the complications of an 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.
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
Previous thyroid treatment
An underactive thyroid can also occur as a side effect or complication of previous treatment to the thyroid gland, such as surgery or a treatment called radioactive iodine therapy.
These treatments are sometimes used for an overactive thyroid (where the thyroid gland produces too much hormone) or thyroid cancer.
Combination therapy
In the UK, combination therapy – using levothyroxine and triiodothyronine (T3) together – isn’t routinely used because there’s insufficient evidence to show it’s better than using levothyroxine alone (monotherapy).
In most cases, suppressing thyroid-stimulating hormone (TSH) using high dose thyroid replacement therapy should be avoided because it carries a risk of causing adverse side effects, such as atrial fibrillation (an irregular and abnormally fast heart rate), strokes, osteoporosis and fracture.
However, this type of treatment may sometimes be recommended in cases where a person has a history of thyroid cancer and there’s a significant risk of it reoccurring.
Complications
If you have an underactive thyroid that goes untreated, a few complications can develop over time.
Heart problems
An untreated underactive thyroid raises your risk of developing cardiovascular disease. This happens because low levels of the hormone thyroxine can push up cholesterol levels in your blood. High cholesterol lets fatty deposits build up in your arteries, narrowing them and restricting blood flow.
If you're being treated for an underactive thyroid and you develop chest pain, contact your doctor so the problem can be checked and treated if needed.
Goitre
A goitre is an abnormal swelling of the thyroid gland that shows up as a lump in the throat. It can develop in people with an underactive thyroid, as the body tries to push the thyroid into producing more hormone.
Pregnancy complications
An underactive thyroid left untreated during pregnancy carries a risk of complications, including:
- pre-eclampsia, which can cause high blood pressure and fluid retention in the mother and growth problems in the baby
- anaemia in the mother
- an underactive thyroid in the baby
- birth defects
- bleeding after birth
- problems with the baby's physical and mental development
- premature birth or a low birthweight
- stillbirth or miscarriage
With the right care from a hormone specialist (an endocrinologist), these problems can usually be prevented. So if you have an underactive thyroid and are pregnant, or trying to become pregnant, let your doctor know.
Myxoedema coma
In very rare cases, a severe underactive thyroid can lead to a life threatening condition called myxoedema coma. Thyroid hormone levels drop very low, and this can bring on confusion, hypothermia and drowsiness.
Myxoedema coma needs emergency treatment in hospital, usually thyroid hormone replacement medicine given directly into a vein. Depending on the case, breathing support, antibiotics or steroid medication (corticosteroids) may also be needed.