Underactive thyroid (hypothyroidism)

What is underactive thyroid?

Underactive thyroid, or hypothyroidism, occurs when your thyroid gland produces less thyroid hormone than it should. This causes your metabolism to run too slowly, leading to things like tiredness, weight gain, slow thinking, low mood, and many more symptoms. The condition is often referred to as underactive thyroid or myxoedema. It may also be called Hashimoto’s disease.

The thyroid gland is a small butterfly shaped gland with two lobes. It sits in the front of your neck, just below the Adam’s apple. The two lobes are joined by tissue called the isthmus. The thyroid is part of the endocrine system, a set of glands that deliver hormones the body needs for many functions.  

The thyroid has two main jobs: the first is to control your metabolism, the rate at which all the chemistry in your body works. The other main thyroid function is to control growth in early life.

The thyroid is regulated by two other glands – the hypothalamus and the pituitary gland. The pituitary produces a hormone called TSH (thyroid stimulating hormone) which triggers the thyroid to produce thyroxine – known as T4. Thyroxine is inactive and must be converted by the body into the active hormone tri-iodothyronine – called T3. 

If cells that need it don’t get enough thyroid hormone, this can lead a wide range of physical and psychological effects. However, with treatment it’s possible to live more or less normally. 

What are the symptoms of underactive thyroid?

Signs and symptoms of underactive thyroid can come on very slowly over months or even years. They include:

  • Weight gain
  • Extreme tiredness
  • Slow movements, thought and speech
  • Pins and needles
  • Breathlessness 
  • Dizziness 
  • Palpitations
  • Loss of sexual interest
  • Depression
  • Dry or ‘gritty’ eyes 
  • Hoarse voice 
  • Difficulty swallowing
  • Hair loss on head and body
  • Dry skin
  • Muscle and joint pain
  • Loss of appetite
  • Constipation

A full list of possible symptoms is available at Thyroid UK

‘I gained an immense amount of weight over a short period of time.’

– response in 2018 HealthUnlocked hypothyroidism survey

What causes underactive thyroid?

The main causes of an underactive thyroid are:

  • Hashimoto’s disease – an autoimmune condition in which the body’s own defences – antibodies or white blood cells – damage the thyroid. Also called chronic lymphocytic thyroiditis, it is the most common cause of hypothyroidism
  • Pituitary or hypothalamic failure, causing secondary hypothyroidism
  • Genetic dysfunction – the thyroid may be underactive at birth, or is ‘programmed’ to fail at some time in adult life (a predisposition)
  • Environmental challenges or deficiencies – chemicals and some foods and drinks can cause problems for the thyroid
  • Previous thyroid surgery or radioactive iodine treatment
  • Treatment for hyperthyroidism, a disease in which too much thyroid hormone is produced
  • Failure to convert inactive T4 hormone to active T3 hormone
  • Receptor resistance – thyroid hormones usually interact with ‘receptors’ in your body’s cells. If the receptors are abnormal, the thyroid hormones cannot do their jobs. 

What is subclinical hypothyroidism?

If the level of hypothyroidism is so slight that people have either no symptoms or only very mild symptoms, it is called ‘subclinical’ hypothyroidism or mild thyroid failure. It is usually found in a blood test either for another disorder or because of a family history of thyroid problems. In subclinical hypothyroidism, only TSH levels are abnormal, while the T4 hormone level is in the normal range.  

Subclinical hypothyroidism often needs no treatment but there is a risk of it eventually developing into hypothyroidism. Your thyroid function should be regularly checked, and you should see your doctor if symptoms become apparent or more severe. 

Who is at risk of underactive thyroid?

Hypothyroidism is mostly diagnosed in women aged 40-60 and is ten times more common in women than men. It often occurs during the menopausal years, when early symptoms are commonly dismissed by both patients and doctors as being part of the menopause.

In the UK 2% of women and 0.2% men are thought to have hypothyroidism. Subclinical hypothyroidism affects 6-8% women and 3% men, and around 2.5% of pregnant women develop hypothyroidism. In the US it is reckoned that 0.3% of the population has overt (symptomatic) hypothyroidism and more than 4.5% have subclinical hypothyroidism. It is believed that up to 20 million Americans have some sort of thyroid disease but 60% are unaware they have the condition.

How is underactive thyroid diagnosed?

Diagnosis of underactive thyroid can take many months or even years because symptoms come on very slowly and can be mistaken for other conditions such as menopause and depression.

The only accurate way to diagnose underactive thyroid is through a blood test.

The tests available to diagnose thyroid disease are:

  • TSH – measuring thyroid stimulating hormone
  • FT4 –  measuring thyroxine levels
  • FT3 – measuring tri-iodothyronine levels
  • TPO Ab – looking for anti-thyroid peroxidase antibody
  • TgAb – looking for anti-thyroglobulin antibody
  • TSI – looking for thyroid stimulating immunoglobulin

However, the TSH test is often the only test performed by doctors, which means there is a possibility that autoimmune hypothyroidism and secondary hypothyroidism may be missed.

A doctor will usually diagnose hypothyroidism if the FT4 level is below the normal range and the TSH is above normal, although some doctors will not diagnose hypothyroidism unless the TSH is above 10 – the normal range is about 0.4 – 4.5. 

If thyroid antibodies are present, subclinical hypothyroidism is more likely to become hypothyroidism.  

There is some evidence that having a fault in a gene called DIO2 can mean that although the body has enough T3 hormone, not enough is delivered to the brain. Testing for the DIO2 gene variation is available. In the UK, however, as of early 2018, it is not provided by the NHS. 

What is the treatment for underactive thyroid?

The most common treatment for hypothyroidism is the medicine levothyroxine, which replaces the thyroxine that the thyroid gland is not producing. Most people feel better on this medication. However, up to 15% of people find that their symptoms don’t fully clear up.

The addition of liothyronine (T3) has been studied in patients, but the results have been inconclusive.  However, research has shown that patients with the DIO2 gene variation had worse baseline scores on the General Health Questionnaire – a tool devised to assess mental wellbeing – than those without the variation. The scores improved when people had liothyronine.

Natural desiccated thyroid (NDT) is a treatment that was used before the manufacture of levothyroxine and liothyronine. Research has found that some patients do very well on this treatment if they have remaining symptoms after using levothyroxine. Many patients taking this medication say they feel much better on this than on levothyroxine.

NDT, however, is not a licensed drug as it was manufactured before licensing began.  It is approved in the United States and Canada and can be prescribed on the NHS in the UK on a “named patient” basis. Many doctors are not aware of the medication until their patients bring it to their attention. Although UK guidelines state that NDT is not recommended, your doctor can prescribe this medication for you, but must write “for hypothyroidism” on the prescription.

The side effects of any thyroid hormone replacement can include palpitations, sweating, feeling very hot, and exhaustion. These are generally caused by taking too much medication and will stop when the dosage is reduced.

‘Once you have the right dose of levo you will soon be back to your old self. You will also know as time passes when the dose is no longer right as you very quickly learn the symptoms. But main thing is life gets back to normal’

– response in 2018 HealthUnlocked hypothyroidism survey

Getting the medication dosage to the ideal level for you is largely a matter of trial and error and it can take time to get this right. The dosage you need can also change over time, so your medication needs to be reviewed regularly.

‘It takes a while for the medication (thyroxine) to work and adjustments may be required over a period of time before you feel better.’

– response in 2018 HealthUnlocked hypothyroidism survey

Some people may have side effects from an intolerance to ‘inactive’ ingredients, like lactose, that are added to medicines for a range of reasons, such as to help keep the active ingredient stable or to ‘bulk up’ a tiny amount of active ingredient so it can be made into a pill or capsule. These side effects vary from person to person.

Managing your medication

Read the Patient Information leaflet that comes with your medicine. This will explain how to take the tablets (i.e. with water at least 30 minutes before food), which medicines will cause problems if you take them at the same time, and how to store the medication.

‘Take your meds with plenty of water as soon as you wake up (approx same time each day) and wait for 30mins before you have any caffeine or something to eat. This is really important as it allows time for the meds to be absorbed and be effective.’

– response in 2018 HealthUnlocked hypothyroidism survey

If possible, try to ensure you are kept on the same make of levothyroxine as different makes can vary in strength and the inactive ingredients used can also vary and may affect you if you switch. 

Thyroid blood tests should be done regularly to check that hormone levels are stable. 

Living with underactive thyroid

Most people with underactive thyroid need treatment for life. However, with the right treatment, you should be able stay healthy and live normally for as long as you would have done without the thyroid disease. 

With any long-term condition, it’s important to keep yourself in general good health – that means eating well, sleeping properly, getting enough exercise and learning to relax and cope with stress.

‘There are worse things in life, so take care of yourself, watch what you eat, exercise and stay positive’

– response in 2018 HealthUnlocked hypothyroidism survey


There’s no hypothyroidism diet as such, but you should focus on getting a balanced diet with vegetables, fruit, whole grains, fish, meat and dairy products. Some people find eating small meals throughout the day helps to keep their energy levels stable.

People with hypothyroidism are advised to avoid highly processed foods and not to take supplements without consulting the doctor. Some high-fibre foods can affect how you absorb levothyroxine. There’s also some evidence that millet should be avoided as it may interfere with the workings of the thyroid gland. Discuss any diet problems with your doctor.

Weight gain is a common symptom of hypothyroidism, so eating well can also help you maintain a healthy weight and this can improve your mood too.


Regular exercise can boost energy, reduce stress, lift your mood and help keep your weight in check. You need aerobic exercise, such as walking or cycling, for heart, lungs and circulation; strength exercises, such as lifting light weights, for your muscles; and flexibility exercises, such as stretching and bending.

‘Try to stay active, get medication checked regularly, and avoid sugar. Start planning nap time and if you still feel tired have a nap.’

– response in 2018 HealthUnlocked hypothyroidism survey

You can do lots of exercise at home without any special equipment – see Health and Fitness on the NHS website for simple exercise information.


Tiredness is a feature of hypothyroidism and one way to combat this is to make sure you sleep well. Try to go to bed and wake up at the same time every day, including at weekends, and aim for from 7 to 9 hours sleep.

There’s much you can do yourself to improve your sleep – see ’10 tips to beat insomnia’ from the NHS

If you continually have trouble falling, or staying, asleep, and this is causing you problems, talk to your doctor.


The stress of coping with any long-term illness can make symptoms worse and lead to low mood, anxiety, depression and other physical and mental problems. Eating well, sleeping properly, and getting enough exercise all help deal with stress but it’s important to be able to relax as well.

There are lots of techniques you can learn – for example deep breathing exercises or meditation – that can help in as little as five minutes a day. The WebMD website list a series of different ways to beat stress


Underactive thyroid can cause complications in pregnancy for both mother and baby. Usually these problems can be avoided with the right treatment, so you should tell your doctor if you have hypothyroidism and are pregnant or trying for a baby. You may get treatment during pregnancy from an endocrinologist, a hormone disorders specialist. 

Other complications

There are several possible complications with hypothyroidism, though they are uncommon in people whose underactive thyroid is being treated.

Cardiovascular disease is a risk as low levels of thyroid hormone lead to raised cholesterol in the blood, which in turn can cause a fatty build-up that narrows your arteries. If you are being treated for hypothyroidism and get chest pain, you should see your doctor. 

Untreated hypothyroidism can cause the thyroid gland to swell and cause a lump in your throat called a goitre. If these are small, they usually cause no problems and will be monitored rather than treated. Goitres that need treating are usually dealt with by surgery or radioiodine treatment.

Myxoedema coma is an extremely rare emergency in which levels of thyroid hormone drop to a critical level causing a low body temperature, confusion, weakness and drowsiness. This is a life-threatening condition that needs urgent hospital treatment

Support for people with underactive thyroid

Many people find that talking with others who have the illness is an invaluable source of information and advice. 

‘Do lots of research, register with a forum and get copies of your blood tests’

– response in 2018 HealthUnlocked hypothyroidism survey

There are numerous organisations that offer information and support to people with hypothyroidism and a range of online communities where you can discuss the condition with others who have it.

Get information and support from:

Apart from online support, most thyroid organisations offer things such as telephone helplines, email enquiry services and networks of local groups where you can meet others with the condition.

Main resources consulted in preparing this information

All sources mentioned here were accessed during February 2018.

·         US National Library of Medicine

·         American Thyroid Association

·         British Thyroid Foundation

·         National Center for Biotechnology Information

·         Healthline

·         Thyroid UK

·         DeCherney A, Nathan L, Laufer N, Roman A. Current diagnosis & treatment: obstetrics & gynecology. 11th ed. ed. New York: McGraw-Hill/Medical; 2013.

·         NHS.UK

·         Thyroid Foundation of Canada

·         Cleveland Clinic

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