What is hypothyroidism?
Hypothyroidism is the name given to the condition resulting from an under-active thyroid gland. This means that it is not producing enough thyroid hormone for the body’s needs.
What causes hypothyroidism?
Hypothyroidism can be caused by:
- Autoimmune thyroid disease – the most common cause. This is a self-destructive process in which the body's immune system attacks the thyroid cells as though they were foreign cells. The most common form is known as 'Hashimoto’s thyroiditis'
- Radioactive iodine treatment, or surgery, to correct hyperthyroidism or to treat thyroid cancer
- Antithyroid drugs if given for an over-active thyroid disorder in too large a dose
- Medicines such as lithium (used for certain mental disorders) and amiodarone (used to control particular heart problems)
- Some cough medicines containing large amounts of iodine can also interfere with the way the thyroid functions
- Some health foods taken in excess, e.g. kelp (seaweed)
- A malfunction of the pituitary gland (a gland in the brain that regulates the thyroid hormones)
- Radiation for head and neck cancers (not common in the UK)
Sometimes hypothyroidism is present from birth. In a few babies, the thyroid does not develop or does not form the thyroid hormones properly. This is known as congenital hypothyroidism.
What are the symptoms of hypothyroidism?
The symptoms begin so gradually that you and your doctor might not notice them until the condition is well advanced. Low levels of thyroid hormone result in a slowing down of the mental and physical processes of the whole body. Once treatment has started these symptoms will improve over time, but if not, you should talk to your doctor. These are the most common symptoms:
- fatigue and tiredness
- increased awareness of the cold
- dry and coarse skin
- dry and thinning hair
- hoarse or croaky voice
- muscle weakness, cramps and aches
- pins and needles in the fingers and hands (carpal tunnel syndrome)
- heavier and longer periods
- fertility problems
- low libido
- weight gain
- puffy face and bags under the eyes
- slow speech, movements and thoughts
- low mood or depression
- memory problems
- difficulty in concentration
- slow heart beat
- slightly raised blood pressure
- raised cholesterol
- slowed growth (in children)
How is hypothyroidism diagnosed?
By a physical examination and blood tests. A thyroid function blood test is a simple and accurate way to check whether your thyroid gland is working properly. An under-active thyroid is typically associated with a thyroid-stimulating hormone (TSH) level above the reference range and a thyroxine (FT4) level that is below the reference range. It is reasonable to have a test for thyroid antibodies to confirm that the cause is autoimmune. Other factors such as common illnesses that can temporarily alter blood test readings will need to be ruled out. Some medicines - prescribed and over-the-counter - can affect results, so it is important to tell your doctor about any medication you are taking.
What is mild thyroid failure or subclinical hypothyroidism?
Sometimes the level of hypothyroidism is so slight that there are no obvious symptoms and it can only be detected by blood tests. It may be discovered as a result of blood tests for another autoimmune disorder or because there is a history of thyroid disorders in the family.
A blood test result showing a slightly raised TSH level with a normal FT4 level indicates that you may have mild thyroid failure or subclinical hypothyroidism, and that you may have an increased risk of eventually developing hypothyroidism. You should have a regular thyroid function test and consult your doctor if you notice any symptoms, as you may benefit from treatment.
What is the treatment for hypothyroidism?
Your doctor will prescribe levothyroxine, a synthetic version of the thyroxine produced by the thyroid gland. Levothyroxine is very pure, and has negligible side-effects when taken in the correct dose.
Levothyroxine doses are dependent upon the person’s body weight. Most patients require between 100 and 150 micrograms a day, but the dose can be lower than 75 micrograms or up to 300 micrograms a day, depending on your needs. If you have severe hypothyroidism or are at risk of heart problems you can expect your doctor to start cautiously and increase the dose gradually. Patience is needed as it can take several months before you feel better and for the thyroid function tests to return to normal or be judged satisfactory by your doctor. During this period you will have regular thyroid function tests, usually every six to eight weeks.
Levothyroxine is best taken in the morning, with water, on an empty stomach, at least half an hour before eating and drinking anything. It is also best taken at least four hours apart from calcium, iron, cholesterol-lowering drugs (cholestyramine, colestipol), and multivitamin tablets, as these too can decrease absorption. Grapefruit on the other hand is known to increase the absorption of levothyroxine due to increased acid in the stomach. There are a number of other drugs that interact with levothyroxine. Always check with your doctor or pharmacy if you are on any other prescription or over-the-counter medication.
It is easy to miss a levothyroxine tablet, but because your body has a big reservoir of thyroxine, you will not notice a difference. However, it is important to take the tablets consistently every day as this can affect your blood test results and your health. Try and devise a system to help you take them every day.
Levothyroxine tablets may deteriorate if subjected to extreme temperatures.
Once the correct dose has been established it is unlikely to vary, although it is still important to have a blood test each year just to make sure. Too much levothyroxine will cause symptoms of an over-active thyroid and too little levothyroxine will not completely resolve symptoms of an under-active thyroid.
The correct dose of levothyroxine is one that restores good health. In most patients this will be associated with a thyroid-stimulating hormone (TSH) reading in the lower part of the reference range and a level of thyroxine (T4) in the blood towards the upper part or even slightly above the reference range.
Some patients treated with levothyroxine have persistent complaints despite serum TSH readings in the reference range. Combination therapy of levothyroxine and tri-iodothyronine (LT4 and LT3) may be considered as an experimental approach under the supervision of an accredited endocrinologist.
If you are planning a pregnancy you should let your doctor know and ideally have a blood test before you conceive. As soon as you know you are pregnant, and if you are already taking levothyroxine, it is recommended that the dosage is increased immediately by 25-50mcg daily. You should then arrange to have a thyroid function test as soon as possible. Even if your thyroid function test is not ideal at the start of pregnancy, your risk of pregnancy complications is only slightly higher than normal and you will still have a good chance of a successful pregnancy outcome. However, your levothyroxine treatment should be adjusted to normalise your thyroid function as soon as possible. (See: Your Guide to Pregnancy and Fertility in Thyroid Disorders.)
Some important points….
- You will normally be looked after by your GP, but will be referred to an endocrinologist - a doctor specialising in thyroid and other endocrine disorders - if there are problems
- Once stable you should have a blood test once a year to check your thyroid hormone levels
- It is important to take your tablets consistently every day as failure to do this can affect your blood test results and your health
- You will need to take levothyroxine for life. Continue taking your tablets, unless advised by a doctor, even if other illness develops
- Once you know you are pregnant it is recommended that the levothyroxine dosage be increased by 25-50mcg daily
- Check with your doctor whether your prescription is exempt from charges
It is well recognised that thyroid problems often run in families and if family members are unwell they should be encouraged to discuss with their own GP whether thyroid testing is warranted.
If you have questions or concerns about your thyroid disorder, you should talk to your doctor or specialist as they will be best placed to advise you. You may also contact the British Thyroid Foundation for further information and support, or if you have any comments about the information contained in this leaflet.
The British Thyroid Foundation
The British Thyroid Foundation is a registered charity: England and Wales No 1006391, Scotland SC046037
The British Thyroid Association - medical professionals encouraging the highest standards in patient care and research
The British Association of Endocrine and Thyroid Surgeons - the representative body of British surgeons who have a specialist interest in surgery of the endocrine glands (thyroid, parathyroid and adrenal)
First issued: 2008
Revised: 2011, 2015
Our literature is reviewed every two years and revised if necessary.
© 2015 BRITISH THYROID FOUNDATION