Revised 2018

Hypothyroidism is a condition where the thyroid gland produces too little thyroid hormone for the body’s needs. It is also known as an under-active thyroid.

  • Hypo - means “under -“
  • Hyper - means “over -“


Common Symptoms

A slowing down of mental and physical processes of the whole body such as

  • Fatigue and tiredness
  • Weight gain
  • Increased awareness of the cold
  • Constipation
  • Dry skin and hair
  • Low mood or depression
  • Memory or concentration difficulties (sometimes referred to as 'brain fog')
  • Heavy periods and fertility problems


  • By a physical examination and blood tests
  • A high thyroid stimulating hormone (TSH) level with a low thyroxine (T4) level indicates hypothyroidism. Rarely, hypothyroidism can occur when both the TSH and T4 are low
  • A slightly raised TSH with a normal T4 is called subclinical, mild, or borderline hypothyroidism
  • Subclinical hypothyroidism can develop into clinical or overt hypothyroidism


Levothyroxine tablets (a synthetic version of thyroxine) taken daily, for life

  • Tell your doctor if you are taking any other medicines or special foods as some can interfere with levothyroxine absorption
  • It is important to take your tablets consistently every day as failure to do this can affect your blood test results and your health
  • If you are planning a baby, 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 (see Pregnancy and Fertility in Thyroid Disorders)


Blood tests are carried out

  • approximately every six to eight weeks after the start of therapy or after a dose change until the correct dose of levothyroxine is established (i.e. the TSH is within the normal reference range)
  • once a year thereafter (except in special circumstances such as pregnancy when more frequent testing is required)

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.

This Quick Guide is one in a series about thyroid disorders. All Quick Guides are available on the British Thyroid Foundation website. A leaflet containing more detailed information about Hypothyroidism is also available.

The British Thyroid Foundation
tel: 01423 810093
The British Thyroid Foundation is a registered charity: England and Wales No 1006391, Scotland SC046037

Membership Information
Quick Guides

Endorsed by:

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: 2010, 2011, 2015, 2018
Our literature is reviewed every two years and revised if necessary.

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