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:
- being sensitive to cold
- weight gain
- slow movements and thoughts
- muscle aches and weakness
- muscle cramps
- dry and scaly skin
- brittle hair and nails
- loss of libido (sex drive)
- pain, numbness and a tingling sensation in the hand and fingers (carpal tunnel syndrome)
- irregular periods or heavy periods
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:
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.
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 website has more information about the different types of thyroid function tests.
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.
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.
Levothyroxine doesn’t usually have any side effects, because the tablets simply replace a missing hormone.
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.
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.
A 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.
If an underactive thyroid isn’t treated during pregnancy, there’s a risk of problems occurring. These include:
- 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
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.
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.